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Position paper on vegetarian diets from the working group of the Italian Society of Human Nutrition

Open AccessPublished:October 31, 2017DOI:https://doi.org/10.1016/j.numecd.2017.10.020

      Highlights

      • Vegetarian diets that include a wide variety of plant foods provide adequate nutrient intake for Italians of all ages.
      • However, vitamin B12 intake may be low, so vitamin-fortified foods/B12 supplements are advised.
      • Vegetarians should eat more protein than recommended for omnivores because of reduced plant protein digestibility.
      • Vegetarians should eat good sources of Ca, Fe and Zn and prepare foods to enhance Ca, Fe and Zn bioavailability.
      • Vegetarians should eat sufficient α-linolenic acid and limit linoleic acid intake.

      Abstract

      Background

      Interest in vegetarian diets is growing in Italy and elsewhere, as government agencies and health/nutrition organizations are emphasizing that regular consumption of plant foods may provide health benefits and help prevent certain diseases.

      Methods and results

      We conducted a Pubmed search, up to September, 2015, for studies on key nutrients (proteins, vitamin B12, iron, zinc, calcium, vitamin D, and n-3 fatty acids) in vegetarian diets. From 295 eligible publications the following emerged: Vegetarians should be encouraged to supplement their diets with a reliable source of vitamin B12 (vitamin-fortified foods or supplements). Since the plant protein digestibility is lower than that of animal proteins it may be appropriate for vegetarians to consume more proteins than recommended for the general population. Vegetarians should also be encouraged to habitually consume good sources of calcium, iron and zinc – particularly vegetables that are low in oxalate and phytate (e.g. Brassicaceae), nuts and seeds, and calcium-rich mineral water. Calcium, iron, and zinc bioavailability can be improved by soaking, germination, and sour-dough leavening that lower the phytate content of pulses and cereals. Vegetarians can ensure good n-3 fatty acid status by habitually consuming good sources of a-linolenic acid (walnuts, flaxseeds, chia seeds, and their oils) and limiting linoleic acid intake (corn and sunflower oils).

      Conclusions

      Well-planned vegetarian diets that include a wide variety of plant foods, and a reliable source of vitamin B12, provide adequate nutrient intake. Government agencies and health/nutrition organizations should provide more educational resources to help Italians consume nutritionally adequate vegetarian diets.

      Keywords

      In response to increasing interest in eating vegetarian in Italy, in 2012 the Italian Society of Human Nutrition (SINU) set up a working group to assess the peer-reviewed literature on vegetarian diets so as to distil scientifically sound advice for the Italian public on how best to maximize the benefits and minimize the risks associated with the different types of vegetarian diet. The present position paper summarizes the evidence pertaining to the availability of proteins, vitamin B12, iron, zinc, calcium, vitamin D, and n-3 fatty acids, in vegetarian diets and the nutritional status of these factors in vegetarians of all ages and lifestyles. These factors are key for vegetarians since they may not always be present in adequate amounts in some types of vegetarian diet. Based on the evidence, the paper makes recommendations intended for those who wish to follow a vegetarian diet.

      Varieties of vegetarian diet

      A vegetarian diet excludes consumption of all types of meat (pork, beef, mutton, lamb, poultry, game), meat products (sausages, salami, pâté, etc.), fish (including sushi), and molluscs and crustaceans, etc. Dairy products, eggs, and honey may be included, so that there are two main types of vegetarian diet:
      • (a)
        Lacto-ovo-vegetarianism (LOV). This excludes meat but includes dairy products, eggs, and honey, together with a wide variety of plant foods. Sub-categories are lacto-vegetarianism (LV) which excludes eggs, and ovo-vegetarianism (OV) which excludes dairy products. And
      • (b)
        Veganism (VEG). This excludes meat, dairy products, eggs, and honey, but includes a wide variety of plant foods.
      The nutritional profiles of LOV and VEG diets vary widely in relation to the types, quantities, and extent of processing of the plant foods consumed; for LOV, the variation is likely to be greatest, since animal products are also consumed.
      However some people adhere to other plant-based diets that limit the foods consumed, and these must be clearly distinguished from LOV and VEG diets. They include:
      • Raw food diet: consisting exclusively of vegetables, including sprouted cereals and pulses, fresh and dried fruits, and seeds, as well as milk and eggs, all of which are mainly eaten raw.
      • Fruit diet: consisting exclusively of fresh and dried fruits, seeds, and some vegetables.
      • Macrobiotic diet: the strictly vegetarian version of this diet consists of cereals, pulses, vegetables, seaweed, and soy products; while dairy products, eggs, and some vegetables are avoided. Fish is consumed by some who adhere to a macrobiotic diet.
      The publications reviewed in this paper mainly concern LOV and VEG diets as eaten in western and Asian countries. Consequently the recommendations mainly pertain to these diets, which are generally defined as “vegetarian”.
      The nutritional adequacy of raw food, fruit and macrobiotic diets has been assessed by very few studies. What evidence is available on these diets is summarized. The claimed health benefits of these diets are not supported by the available evidence, and in many cases these diets may be nutritionally inadequate.

      Methods

      PubMed was searched for studies published up to September 2015. We used keywords (words or MeSH terms) within search strings incorporating various terms for vegetarian diet in combination with words relating to age, bioavailability, and nutritional status, in combination with the nutrients of interest (protein, vitamin B12, calcium, iron, zinc, and n-3 fatty acids). We confined ourselves to PubMed as preliminary searches on EMBASE revealed no additional studies. We also searched the reference lists of retrieved studies. We identified 815 publications: 150 on protein, 149 on vitamin B12, 291 on calcium and vitamin D, 59 on iron, 69 on zinc and 92 on n-3.
      Review team members screened retrieved titles and abstracts and selected articles that seemed pertinent excluding those not in English or not concerned with humans. The full papers were read independently by two team members to select potentially eligible articles. Review team members then used a checklist (different for each study type: systematic review/meta-analysis, randomized controlled trial, cohort or case–control, or cross-sectional study) to arrive at an assessment of the scientific merit and relevance of each paper value. A total of 295 articles were considered eligible following this assessment.

      Protein

      Sources and bioavailability

      There are concerns that a plant-based diet may not contain protein of adequate quality. Protein quality is determined by digestibility and amino acid content [
      • WHO/FAO
      Protein and amino acid requirements in human nutrition.
      ]. Purified or concentrated vegetable proteins (e.g. soy protein, gluten) have high digestibility (>95%) – similar to that of animal proteins. For some intact vegetable products, such as whole cereals and pulses, protein digestibility is lower (around 80–90%). Most other vegetable proteins have lower digestibility (50–80%) because of the presence of plant cell walls and anti-nutritional factors. Food processing and heat treatment also influence protein digestibility.
      Foods of vegetable origin may contain high levels of antinutritional factors, which may be naturally-occurring (e.g. digestive enzyme inhibitors, tannins, phytate, glucosinolates, isothiocyanates), formed during processing (e.g. d-amino acids, lysinoalanine), or due to genetic modification (e.g. lectins) [
      • Gilani G.S.
      • Wu X.C.
      • Cockell K.A.
      Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality.
      ]. Pulses, cereals, potatoes, and tomatoes in particular contain inhibitors of digestive proteolytic enzymes [
      • Friedman M.
      • Brandon D.L.
      Nutritional and health benefits of soy proteins.
      ]. Soybeans are the most concentrated source of trypsin inhibitors, whereas peas and processed soybean products contain considerably lower levels [
      • Gilani G.S.
      • Wu X.C.
      • Cockell K.A.
      Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality.
      ]. Because they are usually proteins, enzyme inhibitors can be inactivated by heat treatment, including extrusion [
      • Gilani G.S.
      • Wu X.C.
      • Cockell K.A.
      Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality.
      ], or removed by other processing procedures [
      • Friedman M.
      • Brandon D.L.
      Nutritional and health benefits of soy proteins.
      ]. Tannins (water-soluble polyphenols) present, for example, in some peas and beans, can complex with proteins reducing digestibility [
      • Gilani G.S.
      • Wu X.C.
      • Cockell K.A.
      Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality.
      ]. Phytate, as acid in seeds, grains and nuts, or salts in other plant tissues, can reduce carboxypeptidase and aminopeptidase activity by chelating cofactors, or by interacting with the enzyme or its substrate [
      • Gilani G.S.
      • Wu X.C.
      • Cockell K.A.
      Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality.
      ]. Germination of seeds and grains produces enzymes that reduce polyphenol and phytate levels in the sprouts to thereby improve protein digestibility. Fermentation can also render the proteins of pulses and cereals more digestible [
      • Inoue G.
      • Fujita Y.
      • Niiyama Y.
      Studies on protein requirements of young men fed egg protein and rice protein with excess and maintenance energy intakes.
      ,
      • Istfan N.
      • Murray E.
      • Janghorbani M.
      • Young V.R.
      An evaluation of the nutritional value of a soy protein concentrate in young adult men using the short-term N-balance method.
      ,
      • Young V.R.
      • Puig M.
      • Queiroz E.
      • Scrimshaw N.S.
      • Rand W.M.
      Evaluation of the protein quality of an isolated soy protein in young men: relative nitrogen requirements and effect of methionine supplementation.
      ].

      Nutritional status of vegetarians at different ages

      Consistent data indicate that the protein needs of vegetarians are easily met when the diet includes a variety of plant foods, and calorie intake is adequate [
      • Inoue G.
      • Fujita Y.
      • Niiyama Y.
      Studies on protein requirements of young men fed egg protein and rice protein with excess and maintenance energy intakes.
      ,
      • Istfan N.
      • Murray E.
      • Janghorbani M.
      • Young V.R.
      An evaluation of the nutritional value of a soy protein concentrate in young adult men using the short-term N-balance method.
      ,
      • Young V.R.
      • Puig M.
      • Queiroz E.
      • Scrimshaw N.S.
      • Rand W.M.
      Evaluation of the protein quality of an isolated soy protein in young men: relative nitrogen requirements and effect of methionine supplementation.
      ]. A 2003 meta-analysis of nitrogen balance studies found that protein requirements (mg N/kg/day) in healthy adults were not influenced by the source (animal, vegetable, mixed) provided that vegetarians consumed either soy protein or a variety of other vegetable proteins [
      • Rand W.M.
      • Pellett P.L.
      • Young V.R.
      Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults.
      ]. However, while soy protein can meet protein needs as efficiently as animal protein, proteins from other plant sources (mainly pulses and cereals) are less well digested. Furthermore, when lysine tends to be the limiting essential amino acid – as in diets based mainly on cereals (especially wheat) – small quantities of other vegetable proteins, such as those from pulses or oily seeds, are required to obtain sufficient lysine and other essential amino acids.

      Pregnancy and breastfeeding

      Inadequate maternal protein intake during pregnancy reduces infant birthweight [
      • Cooper R.
      • Allen A.
      • Goldberg R.
      • Trevisan M.
      • Van Horn L.
      • Liu K.
      • et al.
      Seventh-day adventist adolescents – life-style patterns and cardiovascular risk factors.
      ]. The few studies that investigated birthweight in infants born of vegetarian women [
      • Shull M.W.
      • Reed R.B.
      • Valadian I.
      • Palombo R.
      • Thorne H.
      • Dwyer J.T.
      Velocities of growth in vegetarian preschool children.
      ,
      • Thomas J.
      • Ellis F.R.
      The health of vegans during pregnancy.
      ,
      • Ward R.J.
      • Abraham R.
      • McFadyen I.R.
      • Haines A.D.
      • North W.R.
      • Patel M.
      • et al.
      Assessment of trace metal intake and status in a Gujerati pregnant Asian population and their influence on the outcome of pregnancy.
      ] indicate that average birthweights of infants born to mothers on VEG or LOV diets do not differ significantly from the average of infants born to omnivorous (OMN) mothers [
      • Thomas J.
      • Ellis F.R.
      The health of vegans during pregnancy.
      ,
      • Ward R.J.
      • Abraham R.
      • McFadyen I.R.
      • Haines A.D.
      • North W.R.
      • Patel M.
      • et al.
      Assessment of trace metal intake and status in a Gujerati pregnant Asian population and their influence on the outcome of pregnancy.
      ]. By contrast, the birthweight of infants born to mothers on a macrobiotic diet was significantly lower than expected, and was attributed to lower maternal weight gain during gestation [
      • Thomas J.
      • Ellis F.R.
      The health of vegans during pregnancy.
      ]. The milk of vegetarian mothers is nutritionally adequate, and infants breastfed by well-nourished vegetarian women grow normally [
      • Craig W.J.
      • Mangels A.R.
      Position of the American Dietetic association: vegetarian diets.
      ,
      • Finley D.A.
      • Lonnerdal B.
      • Dewey K.G.
      • Grivetti L.E.
      Breast milk composition: fat content and fatty acid composition in vegetarians and non-vegetarians.
      ]. However milk from women on a macrobiotic diet has a significantly lower protein content than milk from OMN [
      • Dagnelie P.C.
      • van Staveren W.A.
      • Roos A.H.
      • Tuinstra L.G.
      • Burema J.
      Nutrients and contaminants in human milk from mothers on macrobiotic and omnivorous diets.
      ].
      Although infants of vegetarian mothers grow normally during the first six months [
      • Dwyer J.T.
      • Palombo R.
      • Valadian I.
      • Reed R.B.
      Preschoolers on alternate life-style diets. Associations between size and dietary indexes with diets limited in types of animal foods.
      ,
      • O'Connor H.
      • Munas Z.
      • Griffin H.
      • Rooney K.
      • Cheng H.L.
      • Steinbeck K.
      Nutritional adequacy of energy restricted diets for young obese women.
      ], their growth rate is at the lower end of normal – interpreted as due to a propensity of vegetarian mothers to breastfeed for longer [
      • Sanders T.A.
      Growth and development of British vegan children.
      ,
      • van Staveren W.A.
      • Dhuyvetter J.H.
      • Bons A.
      • Zeelen M.
      • Hautvast J.G.
      Food consumption and height/weight status of Dutch preschool children on alternative diets.
      ].
      Studies on infants fed soy-isolate milk formula, irrespective of whether methionine supplemented, indicate no significant differences in growth compared to infants fed conventional cow milk formula [
      • Fomon S.J.
      • Thomas L.N.
      • Filer Jr., L.J.
      • Anderson T.A.
      • Bergmann K.E.
      Requirements for protein and essential amino acids in early infancy. Studies with a soy-isolate formula.
      ]; furthermore, blood markers of protein metabolism are similar [
      • Fomon S.J.
      • Thomas L.N.
      • Filer Jr., L.J.
      • Anderson T.A.
      • Bergmann K.E.
      Requirements for protein and essential amino acids in early infancy. Studies with a soy-isolate formula.
      ,
      • Lasekan J.B.
      • Ostrom K.M.
      • Jacobs J.R.
      • Blatter M.M.
      • Ndife L.I.
      • Gooch III, W.M.
      • et al.
      Growth of newborn, term infants fed soy formulas for 1 year.
      ]. In a 2001 study [
      • Strom B.L.
      • Schinnar R.
      • Ziegler E.E.
      • Barnhart K.T.
      • Sammel M.D.
      • Macones G.A.
      • et al.
      Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood.
      ] no differences were found in average height or weight between young adults fed soy-based formula and those fed cow milk for several months during childhood.

      Preschool children (6 months to 3 years)

      From the limited data available, it would seem that children who follow a LOV diet have similar growth to OMN children [
      • Craig W.J.
      • Mangels A.R.
      Position of the American Dietetic association: vegetarian diets.
      ]. The growth of non-macrobiotic VEG preschool children is also in the normal range [
      • O'Connor H.
      • Munas Z.
      • Griffin H.
      • Rooney K.
      • Cheng H.L.
      • Steinbeck K.
      Nutritional adequacy of energy restricted diets for young obese women.
      ,
      • Sanders T.A.
      Growth and development of British vegan children.
      ,
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ], although they seem to have an initially smaller stature and tend to be leaner than OMN children [
      • O'Connor H.
      • Munas Z.
      • Griffin H.
      • Rooney K.
      • Cheng H.L.
      • Steinbeck K.
      Nutritional adequacy of energy restricted diets for young obese women.
      ,
      • Sanders T.A.
      Growth and development of British vegan children.
      ]. By contrast, preschool children on a macrobiotic diet were reported to have significantly lower growth than those on other vegetarian diets [
      • Dagnelie P.C.
      • van Staveren W.A.
      Macrobiotic nutrition and child health: results of a population-based, mixed-longitudinal cohort study in The Netherlands.
      ,
      • Dwyer J.T.
      • Andrew E.M.
      • Berkey C.
      • Valadian I.
      • Reed R.B.
      Growth in “new” vegetarian preschool children using the Jenss-Bayley curve fitting technique.
      ].

      Children (4–10 years)

      LOV children have similar growth to OMN children [
      • Hebbelinck M.
      • Clarys P.
      • De Malsche M.A.
      Growth, development, and physical fitness of Flemish vegetarian children, adolescents, and young adults.
      ,
      • Sabate J.
      • Lindsted K.D.
      • Harris R.D.
      • Johnston P.K.
      Anthropometric parameters of schoolchildren with different life-styles.
      ,
      • Van Dusseldorp M.
      • Arts I.C.
      • Bergsma J.S.
      • De Jong N.
      • Dagnelie P.C.
      • van Staveren W.A.
      Catch-up growth in children fed a macrobiotic diet in early childhood.
      ]. Non-macrobiotic VEG children tend to grow at standard rates [
      • Hebbelinck M.
      • Clarys P.
      • De Malsche M.A.
      Growth, development, and physical fitness of Flemish vegetarian children, adolescents, and young adults.
      ,
      • O'Connell J.M.
      • Dibley M.J.
      • Sierra J.
      • Wallace B.
      • Marks J.S.
      • Yip R.
      Growth of vegetarian children: the Farm study.
      ], while macrobiotic children grow more slowly [
      • Van Dusseldorp M.
      • Arts I.C.
      • Bergsma J.S.
      • De Jong N.
      • Dagnelie P.C.
      • van Staveren W.A.
      Catch-up growth in children fed a macrobiotic diet in early childhood.
      ]. The average protein intake of vegetarian children meets recommendations [
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ,
      • Ambroszkiewicz J.
      • Klemarczyk W.
      • Gajewska J.
      • Chelchowska M.
      • Laskowska-Klita T.
      Serum concentration of biochemical bone turnover markers in vegetarian children.
      ,
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ,
      • Thane C.W.
      • Bates C.J.
      Dietary intakes and nutrient status of vegetarian preschool children from a British national survey.
      ], although they consume less protein than OMN children [
      • van Staveren W.A.
      • Dhuyvetter J.H.
      • Bons A.
      • Zeelen M.
      • Hautvast J.G.
      Food consumption and height/weight status of Dutch preschool children on alternative diets.
      ,
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ,
      • Ambroszkiewicz J.
      • Klemarczyk W.
      • Gajewska J.
      • Chelchowska M.
      • Laskowska-Klita T.
      Serum concentration of biochemical bone turnover markers in vegetarian children.
      ,
      • Thane C.W.
      • Bates C.J.
      Dietary intakes and nutrient status of vegetarian preschool children from a British national survey.
      ].
      One study found that serum albumin levels were above the normal range in both vegetarian and OMN children [
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ]. Since plant proteins are less digestible and contain fewer essential amino acids than animal proteins, it may be advisable for VEG children to consume more protein. Messina and Mangels [
      • Messina V.
      • Mangels A.R.
      Considerations in planning vegan diets: children.
      ] suggested that protein intake should be increased by 30–35% in VEG children under 2 years, and by 20–30% in 2–6-year-olds [
      • Messina V.
      • Mangels A.R.
      Considerations in planning vegan diets: children.
      ].

      Adolescents (11–18 years)

      The available studies indicate that the growth of LOV children and adolescents is comparable to that of their OMN peers [
      • Cooper R.
      • Allen A.
      • Goldberg R.
      • Trevisan M.
      • Van Horn L.
      • Liu K.
      • et al.
      Seventh-day adventist adolescents – life-style patterns and cardiovascular risk factors.
      ,
      • Hebbelinck M.
      • Clarys P.
      • De Malsche M.A.
      Growth, development, and physical fitness of Flemish vegetarian children, adolescents, and young adults.
      ,
      • Persky V.W.
      • Chatterton R.T.
      • Van Horn L.V.
      • Grant M.D.
      • Langenberg P.
      • Marvin J.
      Hormone levels in vegetarian and nonvegetarian teenage girls: potential implications for breast cancer risk.
      ,
      • Nathan I.
      • Hackett A.F.
      • Kirby S.
      A longitudinal study of the growth of matched pairs of vegetarian and omnivorous children, aged 7–11 years, in the north-west of England.
      ]. However adolescents on a macrobiotic diet have lower growth than reference [
      • Hebbelinck M.
      • Clarys P.
      • De Malsche M.A.
      Growth, development, and physical fitness of Flemish vegetarian children, adolescents, and young adults.
      ,
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ,
      • Nathan I.
      • Hackett A.F.
      • Kirby S.
      A longitudinal study of the growth of matched pairs of vegetarian and omnivorous children, aged 7–11 years, in the north-west of England.
      ,
      • Sabate J.
      • Lindsted K.D.
      • Harris R.D.
      • Sanchez A.
      Attained height of lacto-ovo vegetarian children and adolescents.
      ,
      • Sanders T.A.
      Vegetarian diets and children.
      ]. As regards protein intake, this was lower in VEG [
      • Larsson C.L.
      • Westerterp K.R.
      • Johansson G.K.
      Validity of reported energy expenditure and energy and protein intakes in Swedish adolescent vegans and omnivores.
      ] and LOV [
      • Persky V.W.
      • Chatterton R.T.
      • Van Horn L.V.
      • Grant M.D.
      • Langenberg P.
      • Marvin J.
      Hormone levels in vegetarian and nonvegetarian teenage girls: potential implications for breast cancer risk.
      ,
      • Houghton L.A.
      • Green T.J.
      • Donovan U.M.
      • Gibson R.S.
      • Stephen A.M.
      • O'Connor D.L.
      Association between dietary fiber intake and the folate status of a group of female adolescents.
      ] than OMN in some studies, while in others protein intake was adequate [
      • Cooper R.
      • Allen A.
      • Goldberg R.
      • Trevisan M.
      • Van Horn L.
      • Liu K.
      • et al.
      Seventh-day adventist adolescents – life-style patterns and cardiovascular risk factors.
      ,
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ,
      • Nathan I.
      • Hackett A.F.
      • Kirby S.
      A longitudinal study of the growth of matched pairs of vegetarian and omnivorous children, aged 7–11 years, in the north-west of England.
      ,
      • Perry C.L.
      • McGuire M.T.
      • Neumark-Sztainer D.
      • Story M.
      Adolescent vegetarians: how well do their dietary patterns meet the healthy people 2010 objectives?.
      ].
      Like younger VEG children, VEG adolescents may require more protein than their LOV or OMN counterparts because of the lower digestibility and poorer amino acid composition of plant proteins. Thus, Messina and Mangels [
      • Messina V.
      • Mangels A.R.
      Considerations in planning vegan diets: children.
      ] suggested that active VEG teenagers should obtain 7–10% of their calories from protein, and sedentary teenagers should obtain 10–13% of calories from protein.

      Adults

      Several studies have examined the adequacy of protein intake by adult vegetarians [
      • Andrich D.E.
      • Filion M.E.
      • Woods M.
      • Dwyer J.T.
      • Gorbach S.L.
      • Goldin B.R.
      • et al.
      Relationship between essential amino acids and muscle mass, independent of habitual diets, in pre- and post-menopausal US women.
      ,
      • Caso G.
      • Scalfi L.
      • Marra M.
      • Covino A.
      • Muscaritoli M.
      • McNurlan M.A.
      • et al.
      Albumin synthesis is diminished in men consuming a predominantly vegetarian diet.
      ,
      • Delanghe J.
      • De Slypere J.P.
      • De Buyzere M.
      • Robbrecht J.
      • Wieme R.
      • Vermeulen A.
      Normal reference values for creatine, creatinine, and carnitine are lower in vegetarians.
      ,
      • Huang Y.C.
      • Chang S.J.
      • Chiu Y.T.
      • Chang H.H.
      • Cheng C.H.
      The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians.
      ,
      • Ingenbleek Y.
      • McCully K.S.
      Vegetarianism produces subclinical malnutrition, hyperhomocysteinemia and atherogenesis.
      ,
      • Kniskern M.A.
      • Johnston C.S.
      Protein dietary reference intakes may be inadequate for vegetarians if low amounts of animal protein are consumed.
      ,
      • Laidlaw S.A.
      • Shultz T.D.
      • Cecchino J.T.
      • Kopple J.D.
      Plasma and urine taurine levels in vegans.
      ,
      • Leblanc J.C.
      • Yoon H.
      • Kombadjian A.
      • Verger P.
      Nutritional intakes of vegetarian populations in France.
      ,
      • Sebekova K.
      • Krajcovicova-Kudlackova M.
      • Blazicek P.
      • Parrak V.
      • Schinzel R.
      • Heidland A.
      Functional hyperhomocysteinemia in healthy vegetarians: no association with advanced glycation end products, markers of protein oxidation, or lipid peroxidation after correction with vitamin B(12).
      ,
      • Turner-McGrievy G.M.
      • Barnard N.D.
      • Scialli A.R.
      • Lanou A.J.
      Effects of a low-fat vegan diet and a step II diet on macro- and micronutrient intakes in overweight postmenopausal women.
      ]. Protein intake in VEG and LOV adults is generally lower than in OMN, but meets requirements. Serum albumin was normal in one study on groups of vegetarians, indicating normal protein nutritional status [
      • Caso G.
      • Scalfi L.
      • Marra M.
      • Covino A.
      • Muscaritoli M.
      • McNurlan M.A.
      • et al.
      Albumin synthesis is diminished in men consuming a predominantly vegetarian diet.
      ]. Kniskern and Johnston [
      • Kniskern M.A.
      • Johnston C.S.
      Protein dietary reference intakes may be inadequate for vegetarians if low amounts of animal protein are consumed.
      ] examined food intake over 4 consecutive days in a convenience sample of young adult vegetarian women, finding that animal protein accounted for only 21% of dietary protein, which is below the dietary reference intake (DRI) of animal protein (45–50% of total) considered adequate. The authors suggested that protein DRI for such women should be increased from 0.8 to 1.0 g/kg bodyweight/day to account for the reduced bioavailability of plant proteins.

      Elderly

      Few studies on the nutritional status of vegetarian elderly are available. Protein intake was lower in vegetarian than OMN women [
      • Deriemaeker P.
      • Aerenhouts D.
      • De Ridder D.
      • Hebbelinck M.
      • Clarys P.
      Health aspects, nutrition and physical characteristics in matched samples of institutionalized vegetarian and non-vegetarian elderly (>65 yrs).
      ,
      • Tylavsky F.A.
      • Anderson J.J.
      Dietary factors in bone health of elderly lactoovovegetarian and omnivorous women.
      ], but higher than recommended. In vegetarian men, protein intake was lower than in OMN men, although sufficient to meet requirements [
      • Deriemaeker P.
      • Aerenhouts D.
      • De Ridder D.
      • Hebbelinck M.
      • Clarys P.
      Health aspects, nutrition and physical characteristics in matched samples of institutionalized vegetarian and non-vegetarian elderly (>65 yrs).
      ]. Two studies [
      • Woo J.
      • Kwok T.
      • Ho S.C.
      • Sham A.
      • Lau E.
      Nutritional status of elderly Chinese vegetarians.
      ,
      • Lau E.M.
      • Kwok T.
      • Woo J.
      • Ho S.C.
      Bone mineral density in Chinese elderly female vegetarians, vegans, lacto-vegetarians and omnivores.
      ] that compared protein intake in elderly Chinese vegetarian and OMN females found that energy from protein was lower in vegetarians and did not always meet the DRI; however, serum markers of protein nutritional status do not seem to differ between vegetarian and OMN elderly [
      • Deriemaeker P.
      • Aerenhouts D.
      • De Ridder D.
      • Hebbelinck M.
      • Clarys P.
      Health aspects, nutrition and physical characteristics in matched samples of institutionalized vegetarian and non-vegetarian elderly (>65 yrs).
      ,
      • Woo J.
      • Kwok T.
      • Ho S.C.
      • Sham A.
      • Lau E.
      Nutritional status of elderly Chinese vegetarians.
      ,
      • Brants H.A.
      • Lowik M.R.
      • Westenbrink S.
      • Hulshof K.F.
      • Kistemaker C.
      Adequacy of a vegetarian diet at old age (Dutch Nutrition Surveillance System).
      ].

      Recommendations

      Since the digestibility and essential amino acid content of plant proteins is lower than that of animal proteins, it may be appropriate for vegetarians to consume more protein than recommended for the general population. This increase can be easily achieved, even in the elderly, pregnant/breast-feeding women, and children, by consumption of a wide variety of plant foods.

      Vitamin B12

      Sources and bioavailability

      Vitamin B12 is reliably present in foods of animal origin but only in small amounts. Some algae contain vitamin B12, however, bioavailability varies with algal species and can be very low [
      • Watanabe F.
      • Yabuta Y.
      • Tanioka Y.
      • Bito T.
      Biologically active vitamin B12 compounds in foods for preventing deficiency among vegetarians and elderly subjects.
      ]. Furthermore some algae contain considerable quantities of inactive vitamin B12 analogues, that can interfere with the absorption of active forms of B12 [
      • Watanabe F.
      • Yabuta Y.
      • Tanioka Y.
      • Bito T.
      Biologically active vitamin B12 compounds in foods for preventing deficiency among vegetarians and elderly subjects.
      ]. Until foods like tempeh are consistently shown to improve vitamin B12 status, they should not be relied upon as a source of vitamin B12.
      Vitamin B12 requires intrinsic factor for absorption. Under physiological conditions intrinsic factor-dependent absorption is saturated with 1.5–2.5 μg of the vitamin per meal. Beyond this amount, the bioavailability of B12 decreases markedly.
      Unlike the food-bound form, which must be released from its binding proteins, crystalline forms of vitamin B12 from supplements and fortified foods are in the free form, and can combine directly with haptocorrin for protection and subsequently with intrinsic factor for absorption [
      • Carmel R.
      Malabsorption of food cobalamin.
      ]. Vitamin B12 in supplements is usually highly effective in correcting vitamin B12 deficiency [
      • Allen L.H.
      How common is vitamin B-12 deficiency?.
      ,
      • Campbell A.K.
      • Miller J.W.
      • Green R.
      • Haan M.N.
      • Allen L.H.
      Plasma vitamin B-12 concentrations in an elderly latino population are predicted by serum gastrin concentrations and crystalline vitamin B-12 intake.
      ,
      • Blacher J.
      • Czernichow S.
      • Raphael M.
      • Roussel C.
      • Chadefaux-Vekemans B.
      • Morineau G.
      • et al.
      Very low oral doses of vitamin B-12 increase serum concentrations in elderly subjects with food-bound vitamin B-12 malabsorption.
      ].
      The bioavailability of vitamin B12 in a LOV diet depends on the quantities and types of animal foods (dairy products, eggs) consumed, as well as on the consumption of fortified foods (e.g. breakfast cereals) and supplements. For VEG the only reliable sources of vitamin B12 are fortified foods and supplements.

      Nutritional status of vegetarians at different ages

      Vitamin B12 deficiency develops slowly, as the liver stores sufficient quantities to last several years. If storage is limited or requirements are high (e.g. in infants breastfed by VEG mothers not taking supplements), clinical symptoms may develop earlier. Folate intake is high in vegetarians, so the typical haematological alterations of vitamin B12 deficiency may not appear; however high folate cannot prevent the deleterious effects of B12 deficiency on the nervous system. Since plasma B12 includes variable amounts of the metabolically inactive form complexed with circulating haptocorrin [
      • SINU
      Intake levels of reference of nutrients and energy-IV revision.
      ], B12 status is optimally assessed in vegetarians using the markers homocysteine, holotranscobalamin II and methylmalonic acid [
      • Mangels R.
      • Messina V.
      • Messina M.
      The dietitian's guide to vegetarian diets.
      ]. Increased methylmalonic acid levels may be present in persons with serum vitamin B12 in the commonly accepted normal range (>156 pmol/L) but not exceeding 360 pmol/L (488 pg/mL) [
      • Herrmann W.
      • Schorr H.
      • Purschwitz K.
      • Rassoul F.
      • Richter V.
      Total homocysteine, vitamin B(12), and total antioxidant status in vegetarians.
      ], so a reference limit of 360 pmol/L for serum vitamin B12 has been proposed [
      • Herrmann W.
      • Geisel J.
      Vegetarian lifestyle and monitoring of vitamin B-12 status.
      ] and should be adopted if holotranscobalamin II levels are not available.

      Pregnancy and breastfeeding

      One study found that vitamin B12 levels in a sample of pregnant LOV women were significantly lower than those of OMN controls: high plasma homocysteine plus low serum vitamin B12 was present in 25% of the LOV women in at least one trimester [
      • Koebnick C.
      • Hoffmann I.
      • Dagnelie P.C.
      • Heins U.A.
      • Wickramasinghe S.N.
      • Ratnayaka I.D.
      • et al.
      Long-term ovo-lacto vegetarian diet impairs vitamin B-12 status in pregnant women.
      ].

      Preschool children (6 months to 3 years)

      In a review of about a hundred case reports of B12-deficient children from various countries it was found that two thirds were born to vegetarian mothers, and a quarter were born to mothers with pernicious anaemia [
      • Mathey C.
      • Di Marco J.N.
      • Poujol A.
      • Cournelle M.A.
      • Brevaut V.
      • Livet M.O.
      • et al.
      [Failure to thrive and psychomotor regression revealing vitamin B12 deficiency in 3 infants].
      ]. Vitamin B12 status seems to have been evaluated in only two cohorts of macrobiotic children. In a Dutch cohort, macrobiotic children had significantly lower “true” cobalamin levels than controls [
      • Dagnelie P.C.
      • van Staveren W.A.
      Macrobiotic nutrition and child health: results of a population-based, mixed-longitudinal cohort study in The Netherlands.
      ,
      • Dagnelie P.C.
      • van Staveren W.A.
      • Hautvast J.G.
      Stunting and nutrient deficiencies in children on alternative diets.
      ]. In a Norwegian cohort 85.4% had high serum levels (>0.43 mmol/L) of methylmalonic acid [
      • Schneede J.
      • Dagnelie P.C.
      • van Staveren W.A.
      • Vollset S.E.
      • Refsum H.
      • Ueland P.M.
      Methylmalonic acid and homocysteine in plasma as indicators of functional cobalamin deficiency in infants on macrobiotic diets.
      ].

      Children and adolescents (4–18 years)

      All available studies indicate low B12 status in macrobiotic persons of this age group [
      • Dhonukshe-Rutten R.A.
      • van Dusseldorp M.
      • Schneede J.
      • de Groot L.C.
      • van Staveren W.A.
      Low bone mineral density and bone mineral content are associated with low cobalamin status in adolescents.
      ,
      • Miller D.R.
      • Specker B.L.
      • Ho M.L.
      • Norman E.J.
      Vitamin B-12 status in a macrobiotic community.
      ,
      • van Dusseldorp M.
      • Schneede J.
      • Refsum H.
      • Ueland P.M.
      • Thomas C.M.
      • de Boer E.
      • et al.
      Risk of persistent cobalamin deficiency in adolescents fed a macrobiotic diet in early life.
      ]. By contrast, most available studies on non-macrobiotic vegetarians (LOV + VEG, LOV) indicate that B12 (and when evaluated, homocysteine) levels are within normal range [
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ,
      • Thane C.W.
      • Bates C.J.
      Dietary intakes and nutrient status of vegetarian preschool children from a British national survey.
      ,
      • Ambroszkiewicz J.
      • Klemarczyk W.
      • Chelchowska M.
      • Gajewska J.
      • Laskowska-Klita T.
      Serum homocysteine, folate, vitamin B12 and total antioxidant status in vegetarian children.
      ,
      • Laskowska-Klita T.
      • Chelchowska M.
      • Ambroszkiewicz J.
      • Gajewska J.
      • Klemarczyk W.
      The effect of vegetarian diet on selected essential nutrients in children.
      ,
      • Yen C.E.
      • Yen C.H.
      • Cheng C.H.
      • Huang Y.C.
      Vitamin B-12 status is not associated with plasma homocysteine in parents and their preschool children: lacto-ovo, lacto, and ovo vegetarians and omnivores.
      ]. A small study on 6 LOV Asians who had migrated to Auckland found that half had asymptomatic B12 deficiency [
      • Rush E.C.
      • Chhichhia P.
      • Hinckson E.
      • Nabiryo C.
      Dietary patterns and vitamin B(12) status of migrant Indian preadolescent girls.
      ].

      Adults and elderly

      Numerous studies on vitamin B12 status in adult vegetarians have been conducted worldwide; many included elderly people, thus results of studies which included both adults and elderly are presented together.
      A number of studies on vegetarians (LOV, LV, LOV + VEG) found that mean B12 plasma levels were in the normal range or did not differ from those of OMN [
      • Herrmann W.
      • Schorr H.
      • Purschwitz K.
      • Rassoul F.
      • Richter V.
      Total homocysteine, vitamin B(12), and total antioxidant status in vegetarians.
      ,
      • Herrmann W.
      The importance of hyperhomocysteinemia as a risk factor for diseases: an overview.
      ,
      • Majchrzak D.
      • Singer I.
      • Manner M.
      • Rust P.
      • Genser D.
      • Wagner K.H.
      • et al.
      B-vitamin status and concentrations of homocysteine in Austrian omnivores, vegetarians and vegans.
      ,
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ].
      Twenty-three studies specifically on LOV found compromised vitamin B12 status – as low serum B12 [
      • Huang Y.C.
      • Chang S.J.
      • Chiu Y.T.
      • Chang H.H.
      • Cheng C.H.
      The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians.
      ,
      • Woo J.
      • Kwok T.
      • Ho S.C.
      • Sham A.
      • Lau E.
      Nutritional status of elderly Chinese vegetarians.
      ,
      • Bissoli L.
      • Di Francesco V.
      • Ballarin A.
      • Mandragona R.
      • Trespidi R.
      • Brocco G.
      • et al.
      Effect of vegetarian diet on homocysteine levels.
      ,
      • Gammon C.S.
      • von Hurst P.R.
      • Coad J.
      • Kruger R.
      • Stonehouse W.
      Vegetarianism, vitamin B12 status, and insulin resistance in a group of predominantly overweight/obese South Asian women.
      ,
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Gilsing A.M.
      • Crowe F.L.
      • Lloyd-Wright Z.
      • Sanders T.A.
      • Appleby P.N.
      • Allen N.E.
      • et al.
      Serum concentrations of vitamin B12 and folate in British male omnivores, vegetarians and vegans: results from a cross-sectional analysis of the EPIC-Oxford cohort study.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Hokin B.D.
      • Butler T.
      Cyanocobalamin (vitamin B-12) status in Seventh-day Adventist ministers in Australia.
      ,
      • Hung C.J.
      • Huang P.C.
      • Lu S.C.
      • Li Y.H.
      • Huang H.B.
      • Lin B.F.
      • et al.
      Plasma homocysteine levels in Taiwanese vegetarians are higher than those of omnivores.
      ,
      • Karabudak E.
      • Kiziltan G.
      • Cigerim N.
      A comparison of some of the cardiovascular risk factors in vegetarian and omnivorous Turkish females.
      ,
      • Krajcovicova-Kudlackova M.
      • Blazicek P.
      • Kopcova J.
      • Bederova A.
      • Babinska K.
      Homocysteine levels in vegetarians versus omnivores.
      ,
      • Krivosikova Z.
      • Krajcovicova-Kudlackova M.
      • Spustova V.
      • Stefikova K.
      • Valachovicova M.
      • Blazicek P.
      • et al.
      The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet.
      ,
      • Kwok T.
      • Cheng G.
      • Woo J.
      • Lai W.K.
      • Pang C.P.
      Independent effect of vitamin B12 deficiency on hematological status in older Chinese vegetarian women.
      ,
      • Mann N.J.
      • Li D.
      • Sinclair A.J.
      • Dudman N.P.
      • Guo X.W.
      • Elsworth G.R.
      • et al.
      The effect of diet on plasma homocysteine concentrations in healthy male subjects.
      ,
      • Reddy S.
      • Sanders T.A.
      Haematological studies on pre-menopausal Indian and Caucasian vegetarians compared with Caucasian omnivores.
      ,
      • Refsum H.
      • Yajnik C.S.
      • Gadkari M.
      • Schneede J.
      • Vollset S.E.
      • Orning L.
      • et al.
      Hyperhomocysteinemia and elevated methylmalonic acid indicate a high prevalence of cobalamin deficiency in Asian Indians.
      ,
      • Su T.C.
      • Jeng J.S.
      • Wang J.D.
      • Torng P.L.
      • Chang S.J.
      • Chen C.F.
      • et al.
      Homocysteine, circulating vascular cell adhesion molecule and carotid atherosclerosis in postmenopausal vegetarian women and omnivores.
      ], high serum methylmalonic acid [
      • Herrmann W.
      • Schorr H.
      • Purschwitz K.
      • Rassoul F.
      • Richter V.
      Total homocysteine, vitamin B(12), and total antioxidant status in vegetarians.
      ,
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ,
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ], high homocysteine [
      • Huang Y.C.
      • Chang S.J.
      • Chiu Y.T.
      • Chang H.H.
      • Cheng C.H.
      The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians.
      ,
      • Bissoli L.
      • Di Francesco V.
      • Ballarin A.
      • Mandragona R.
      • Trespidi R.
      • Brocco G.
      • et al.
      Effect of vegetarian diet on homocysteine levels.
      ,
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Hung C.J.
      • Huang P.C.
      • Lu S.C.
      • Li Y.H.
      • Huang H.B.
      • Lin B.F.
      • et al.
      Plasma homocysteine levels in Taiwanese vegetarians are higher than those of omnivores.
      ,
      • Karabudak E.
      • Kiziltan G.
      • Cigerim N.
      A comparison of some of the cardiovascular risk factors in vegetarian and omnivorous Turkish females.
      ,
      • Krajcovicova-Kudlackova M.
      • Blazicek P.
      • Kopcova J.
      • Bederova A.
      • Babinska K.
      Homocysteine levels in vegetarians versus omnivores.
      ,
      • Krivosikova Z.
      • Krajcovicova-Kudlackova M.
      • Spustova V.
      • Stefikova K.
      • Valachovicova M.
      • Blazicek P.
      • et al.
      The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet.
      ,
      • Mann N.J.
      • Li D.
      • Sinclair A.J.
      • Dudman N.P.
      • Guo X.W.
      • Elsworth G.R.
      • et al.
      The effect of diet on plasma homocysteine concentrations in healthy male subjects.
      ,
      • Su T.C.
      • Jeng J.S.
      • Wang J.D.
      • Torng P.L.
      • Chang S.J.
      • Chen C.F.
      • et al.
      Homocysteine, circulating vascular cell adhesion molecule and carotid atherosclerosis in postmenopausal vegetarian women and omnivores.
      ], or low holotranscobalamin II [
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ]. One study [
      • Chen C.W.
      • Lin Y.L.
      • Lin T.K.
      • Lin C.T.
      • Chen B.C.
      • Lin C.L.
      Total cardiovascular risk profile of Taiwanese vegetarians.
      ] reported normal homocysteine levels in vegetarians, which were however higher than in OMN. Another study [
      • Majchrzak D.
      • Singer I.
      • Manner M.
      • Rust P.
      • Genser D.
      • Wagner K.H.
      • et al.
      B-vitamin status and concentrations of homocysteine in Austrian omnivores, vegetarians and vegans.
      ] found that serum B12 levels in vegetarians were not significantly lower than those in OMN. Finally, a study that examined serum B12, methylmalonic acid, homocysteine and holotranscobalamin II found that LOV had lower B12 status than OMN, but differences were not significant in the LOV subgroup taking B12 supplements [
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ].
      Sixteen studies on VEG found compromised B12 status as low serum B12 [
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ,
      • Bissoli L.
      • Di Francesco V.
      • Ballarin A.
      • Mandragona R.
      • Trespidi R.
      • Brocco G.
      • et al.
      Effect of vegetarian diet on homocysteine levels.
      ,
      • Gilsing A.M.
      • Crowe F.L.
      • Lloyd-Wright Z.
      • Sanders T.A.
      • Appleby P.N.
      • Allen N.E.
      • et al.
      Serum concentrations of vitamin B12 and folate in British male omnivores, vegetarians and vegans: results from a cross-sectional analysis of the EPIC-Oxford cohort study.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Hokin B.D.
      • Butler T.
      Cyanocobalamin (vitamin B-12) status in Seventh-day Adventist ministers in Australia.
      ,
      • Krajcovicova-Kudlackova M.
      • Blazicek P.
      • Kopcova J.
      • Bederova A.
      • Babinska K.
      Homocysteine levels in vegetarians versus omnivores.
      ,
      • Mann N.J.
      • Li D.
      • Sinclair A.J.
      • Dudman N.P.
      • Guo X.W.
      • Elsworth G.R.
      • et al.
      The effect of diet on plasma homocysteine concentrations in healthy male subjects.
      ,
      • Bar-Sella P.
      • Rakover Y.
      • Ratner D.
      Vitamin B12 and folate levels in long-term vegans.
      ,
      • Crane M.
      • Sample C.
      • Patchett S.
      • Register D.
      Vitamin B12 in total vegetarians (vegans).
      ,
      • Crane M.
      • Sample C.
      • Register D.
      • Lukens R.
      • Gregory R.
      Cobalamin (CBL) studies on two total vegetarian (vegan) families.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      The usefulness of holotranscobalamin in predicting vitamin B12 status in different clinical settings.
      ,
      • Waldmann A.
      • Koschizke J.W.
      • Leitzmann C.
      • Hahn A.
      Homocysteine and cobalamin status in German vegans.
      ], high serum methylmalonic acid [
      • Herrmann W.
      • Schorr H.
      • Purschwitz K.
      • Rassoul F.
      • Richter V.
      Total homocysteine, vitamin B(12), and total antioxidant status in vegetarians.
      ,
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ,
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      The usefulness of holotranscobalamin in predicting vitamin B12 status in different clinical settings.
      ], high homocysteine [
      • Majchrzak D.
      • Singer I.
      • Manner M.
      • Rust P.
      • Genser D.
      • Wagner K.H.
      • et al.
      B-vitamin status and concentrations of homocysteine in Austrian omnivores, vegetarians and vegans.
      ,
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ,
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Krajcovicova-Kudlackova M.
      • Blazicek P.
      • Kopcova J.
      • Bederova A.
      • Babinska K.
      Homocysteine levels in vegetarians versus omnivores.
      ,
      • Mann N.J.
      • Li D.
      • Sinclair A.J.
      • Dudman N.P.
      • Guo X.W.
      • Elsworth G.R.
      • et al.
      The effect of diet on plasma homocysteine concentrations in healthy male subjects.
      ,
      • Waldmann A.
      • Koschizke J.W.
      • Leitzmann C.
      • Hahn A.
      Homocysteine and cobalamin status in German vegans.
      ] and low holotranscobalamin II [
      • Geisel J.
      • Schorr H.
      • Bodis M.
      • Isber S.
      • Hubner U.
      • Knapp J.P.
      • et al.
      The vegetarian lifestyle and DNA methylation.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Geisel J.
      The usefulness of holotranscobalamin in predicting vitamin B12 status in different clinical settings.
      ]. Two of these studies included VEG on vitamin B12 supplements [
      • Bissoli L.
      • Di Francesco V.
      • Ballarin A.
      • Mandragona R.
      • Trespidi R.
      • Brocco G.
      • et al.
      Effect of vegetarian diet on homocysteine levels.
      ,
      • Herrmann W.
      • Schorr H.
      • Obeid R.
      • Geisel J.
      Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid.
      ]. Another study that included VEG supplement users found that mean serum B12 and methylmalonic acid levels did not differ between VEG and OMN, nevertheless 10 of the 25 recruited VEG had vitamin B12 deficit as indicated by macrocytosis, circulating vitamin B12 concentrations < 150 pmol/L, or serum methylmalonic acid > 376 nmol/L [
      • Haddad E.H.
      • Berk L.S.
      • Kettering J.D.
      • Hubbard R.W.
      • Peters W.R.
      Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians.
      ]. In a prospective study on 20 adult OMN followed for 5 years while on a VEG diet, B12 levels were reduced only in those who did not take supplements [
      • Madry E.
      • Lisowska A.
      • Grebowiec P.
      • Walkowiak J.
      The impact of vegan diet on B-12 status in healthy omnivores: five-year prospective study.
      ].
      The only available study on macrobiotic adults (who occasionally consumed animal products) reported that 51% had low serum B12, and 30% had high urinary methylmalonic acid [
      • Miller D.R.
      • Specker B.L.
      • Ho M.L.
      • Norman E.J.
      Vitamin B-12 status in a macrobiotic community.
      ].
      Two studies evaluated B12 in VEG who mainly [
      • Donaldson M.S.
      Metabolic vitamin B12 status on a mostly raw vegan diet with follow-up using.
      ] or entirely [
      • Rauma A.L.
      • Torronen R.
      • Hanninen O.
      • Mykkanen H.
      Vitamin B-12 status of long-term adherents of a strict uncooked vegan diet (“living food diet”) is compromised.
      ] ate uncooked food. High urinary methylmalonic acid (≥4.0 μg/mg creatinine) was present in 47% [
      • Donaldson M.S.
      Metabolic vitamin B12 status on a mostly raw vegan diet with follow-up using.
      ] and serum low B12 (<200 pmol/L) was present in 57% [
      • Rauma A.L.
      • Torronen R.
      • Hanninen O.
      • Mykkanen H.
      Vitamin B-12 status of long-term adherents of a strict uncooked vegan diet (“living food diet”) is compromised.
      ]. A study on raw foodists found increased homocysteine levels due to B12 deficiency in all participants (mixed, LOV and VEG), but LOV and VEG had lower serum B12 and higher total plasma homocysteine than mixed raw foodists [
      • Koebnick C.
      • Garcia A.L.
      • Dagnelie P.C.
      • Strassner C.
      • Lindemans J.
      • Katz N.
      • et al.
      Long-term consumption of a raw food diet is associated with favorable serum LDL cholesterol and triglycerides but also with elevated plasma homocysteine and low serum HDL cholesterol in humans.
      ].
      A meta-analysis of 17 studies that compared homocysteine and B12 levels in vegetarians (3230 LOV/LV/VEG) with those in OMN [
      • Obersby D.
      • Chappell D.C.
      • Dunnett A.
      • Tsiami A.A.
      Plasma total homocysteine status of vegetarians compared with omnivores: a systematic review and meta-analysis.
      ] found that VEG had the highest mean homocysteine values, and lowest mean B12 levels, while levels in LOV were intermediate between those of VEG and OMN. In only two of these studies were mean plasma levels of homocysteine and B12 similar to those in OMN [
      • Yen C.E.
      • Yen C.H.
      • Cheng C.H.
      • Huang Y.C.
      Vitamin B-12 status is not associated with plasma homocysteine in parents and their preschool children: lacto-ovo, lacto, and ovo vegetarians and omnivores.
      ,
      • Haddad E.H.
      • Berk L.S.
      • Kettering J.D.
      • Hubbard R.W.
      • Peters W.R.
      Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians.
      ].

      Recommendations

      The vitamin B12 status of vegetarians should be monitored regularly. All vegetarians should be encouraged to include a reliable source of vitamin B12 in their diet (vitamin-fortified foods or supplement). Persons taking B12 tablets should be encouraged to chew them slowly or allow them to dissolve under the tongue to optimise absorption. For children, droplet formulations are suitable. In view of data [
      • Roman V.B.
      • Ribas B.L.
      • Ngo J.
      • Gurinovic M.
      • Novakovic R.
      • Cavelaars A.
      • et al.
      Projected prevalence of inadequate nutrient intakes in Europe.
      ,
      • Doets E.L.
      • In 't Veld P.H.V.
      • Szczecinska A.
      • Dhonukshe-Rutten R.A.
      • Cavelaars A.E.
      • van 't Veer P.
      • et al.
      Systematic review on daily vitamin B12 losses and bioavailability for deriving recommendations on vitamin B12 intake with the factorial approach.
      ] indicating that B12 absorption is often less than 50% [
      • SINU
      Intake levels of reference of nutrients and energy-IV revision.
      ], the European Food Safety Authority recommends that vitamin B12 absorption should be assumed to be 40% [
      • EFSA
      Scientific opinion on dietary reference values for cobalamin (vitamin B12).
      ] when formulating recommended daily intakes, which should thus be 4 μg/day or greater. We therefore propose that, for preserving normal B12 levels in vegetarians, intake should adhere to the recommendations in Table 1. If B12 deficiency is discovered, supplementation with crystalline cobalamin should begin immediately at doses above 4 μg/day.
      Table 1Recommended dietary supplement values for preserving normal B12 levels in persons becoming vegetarians.
      AgeLARN
      LARN is an Italian acronym meaning Reference Levels of Nutrient and Energy Intake for the Italian Population.
      (PRI)
      Population reference intake.
      (μg/day)
      EFSA
      European Food Safety Authority.
      (AI)
      Adequate intake.
      (μg/day)
      Daily multi-doseDaily single-dose (μg/day)
      6–12 months0.71.51 μg × 25
      1–3 years0.91.51 μg × 25
      4–6 years1.11.52 μg × 225
      7–10 years1.62.52 μg × 225
      11–14 years2.23.52 μg × 350
      15–64 years2.44.02 μg × 350
      65+ years2.44.02 μg × 350
      Pregnancy2.64.52 μg × 350
      Breastfeeding2.85.02 μg × 350
      a LARN is an Italian acronym meaning Reference Levels of Nutrient and Energy Intake for the Italian Population.
      b European Food Safety Authority.
      c Population reference intake.
      d Adequate intake.

      Calcium

      Sources and bioavailability

      Several plant foods, particularly leafy vegetables pulses, and nuts, contain good quantities of calcium, however the bioavailability of this mineral is inversely proportional to the amounts of oxalate and phytate in the diet [
      • Weaver C.M.
      • Plawecki K.L.
      Dietary calcium: adequacy of a vegetarian diet.
      ,
      • Weaver C.M.
      • Proulx W.R.
      • Heaney R.
      Choices for achieving adequate dietary calcium with a vegetarian diet.
      ] which are abundant in spinach, Swiss chard, and beet leaves. Dietary fibre seems not to impair calcium absorption, since in one study more calcium was absorbed from kale than cow milk [
      • Heaney R.P.
      • Weaver C.M.
      Calcium absorption from kale.
      ].
      Regardless of solubility, the calcium from calcium salts used to fortify foods is absorbed with similar efficiency to the calcium in cow milk [
      • Heaney R.P.
      • Recker R.R.
      • Weaver C.M.
      Absorbability of calcium sources: the limited role of solubility.
      ] except that the absorption from calcium citrate malate is slightly higher [
      • Weaver C.M.
      • Proulx W.R.
      • Heaney R.
      Choices for achieving adequate dietary calcium with a vegetarian diet.
      ]. The tricalcium phosphate used to fortify soy milk is absorbed with only about 75% of the efficiency of cow milk calcium [
      • Heaney R.P.
      • Dowell M.S.
      • Rafferty K.
      • Bierman J.
      Bioavailability of the calcium in fortified soy imitation milk, with some observations on method.
      ]. The calcium from the calcium chloride and calcium sulphate used to produce tofu has similar bioavailability to the calcium from milk [
      • Weaver C.M.
      • Heaney R.P.
      • Connor L.
      • Martin B.R.
      • Smith D.L.
      • Nielsen S.
      Bioavailability of calcium from tofu as compared with milk in premenopausal women.
      ]. The bioavailability of calcium from mineral water is similar to or better than that from milk [
      • Heaney R.P.
      Absorbability and utility of calcium in mineral waters.
      ]. Calcium absorption from water is improved when water is consumed with food [
      • Van Dokkum W.
      • De La Guéronnière V.
      • Schaafsma G.
      • Bouley C.
      • Luten J.
      • Latge C.
      Bioavailability of calcium of fresh cheeses, enteral food and mineral water. A study with stable calcium isotopes in young adult women.
      ].
      Because sodium and calcium share proximal renal tubule transport systems, high sodium intake promotes calcium excretion [
      • Weaver C.M.
      • Proulx W.R.
      • Heaney R.
      Choices for achieving adequate dietary calcium with a vegetarian diet.
      ].

      Nutritional status of vegetarians at different ages

      Calcium status has been assessed in vegetarians by various methods: dietary calcium intake, serum calcium, ionized serum calcium, bone mineral density (BMD), and bone mineral content (BMC). In physiological conditions, serum calcium is maintained within narrow limits (2.25–2.60 mmol/L total serum calcium or 1.1–1.4 mmol/L ionized form) irrespective of calcium intake, with mobilization from bone if necessary. BMD and BMC are sensitive to changes in calcium intake over the long-term (>1 year) [
      • Gibson R.S.
      Principles of nutritional assessment.
      ] and are not now used to assess calcium status.

      Pregnancy and breastfeeding

      A study [
      • Specker B.L.
      • Tsang R.C.
      • Ho M.
      • Miller D.
      Effect of vegetarian diet on serum 1,25-dihydroxyvitamin D concentrations during lactation.
      ,
      • Specker B.L.
      Nutritional concerns of lactating women consuming vegetarian diets.
      ] on breastfeeding women found that calcium intake was lower and 1,25-dihydroxy vitamin D blood levels significantly higher in macrobiotic women than OMN controls, while blood parathyroid hormone levels were similar. The higher 1,25-dihydroxy vitamin D levels suggest a hormonal response, in macrobiotic women, to low dietary calcium and lactation, that may increase the efficiency of calcium absorption [
      • Specker B.L.
      • Tsang R.C.
      • Ho M.
      • Miller D.
      Effect of vegetarian diet on serum 1,25-dihydroxyvitamin D concentrations during lactation.
      ,
      • Specker B.L.
      Nutritional concerns of lactating women consuming vegetarian diets.
      ].

      Preschool children (6 months to 3 years)

      Only one study on this age group seems to be available: it followed a cohort of macrobiotic children from birth [
      • Dagnelie P.C.
      • Vergote F.J.
      • van Staveren W.A.
      • van den B.H.
      • Dingjan P.G.
      • Hautvast J.G.
      High prevalence of rickets in infants on macrobiotic diets.
      ,
      • Dagnelie P.C.
      • van Dusseldorp M.
      • van Staveren W.A.
      • Hautvast J.G.
      Effects of macrobiotic diets on linear growth in infants and children until 10 years of age.
      ]. At 10–20 months calcium intake and vitamin D in blood were significantly lower in the macrobiotic infants than OMN controls. At the same time (examination in August–November) subclinical or clinical rickets was present in 17% and 28%, respectively, of macrobiotic infants compared to 0% in controls. At follow-up of a subsample of 25 macrobiotic infants in March–April, physical symptoms of rickets were present in 55% of macrobiotic infants [
      • Dagnelie P.C.
      • Vergote F.J.
      • van Staveren W.A.
      • van den B.H.
      • Dingjan P.G.
      • Hautvast J.G.
      High prevalence of rickets in infants on macrobiotic diets.
      ,
      • Dagnelie P.C.
      • van Dusseldorp M.
      • van Staveren W.A.
      • Hautvast J.G.
      Effects of macrobiotic diets on linear growth in infants and children until 10 years of age.
      ].

      Children and adolescents (4–18 years)

      Of several studies [
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ,
      • Ambroszkiewicz J.
      • Klemarczyk W.
      • Gajewska J.
      • Chelchowska M.
      • Laskowska-Klita T.
      Serum concentration of biochemical bone turnover markers in vegetarian children.
      ,
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ,
      • Thane C.W.
      • Bates C.J.
      Dietary intakes and nutrient status of vegetarian preschool children from a British national survey.
      ,
      • Larsson C.L.
      • Johansson G.K.
      Dietary intake and nutritional status of young vegans and omnivores in Sweden.
      ,
      • Donovan U.M.
      • Gibson R.S.
      Dietary intakes of adolescent females consuming vegetarian, semi-vegetarian, and omnivorous diets.
      ] on non-macrobiotic vegetarians, only one, on Chinese vegetarian children [
      • Leung S.S.
      • Lee R.H.
      • Sung R.Y.
      • Luo H.Y.
      • Kam C.W.
      • Yuen M.P.
      • et al.
      Growth and nutrition of Chinese vegetarian children in Hong Kong.
      ], found that calcium intake and BMD were similar to those in OMN children. The other studies found that vegetarian children had lower calcium intake than OMN [
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ,
      • Thane C.W.
      • Bates C.J.
      Dietary intakes and nutrient status of vegetarian preschool children from a British national survey.
      ]. In a large cohort of macrobiotic adolescents evaluated at various times from 1985 [
      • Parsons T.J.
      • van Dusseldorp M.
      • van der Vliet M.
      • van de Werken K.
      • Schaafsma G.
      • van Staveren W.A.
      Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life.
      ], calcium intake and BMC/BMD, but not 1,25-dihdroxyvitamin D, were significantly lower than in OMN controls [
      • Dhonukshe-Rutten R.A.
      • van Dusseldorp M.
      • Schneede J.
      • de Groot L.C.
      • van Staveren W.A.
      Low bone mineral density and bone mineral content are associated with low cobalamin status in adolescents.
      ,
      • Parsons T.J.
      • van Dusseldorp M.
      • van der Vliet M.
      • van de Werken K.
      • Schaafsma G.
      • van Staveren W.A.
      Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life.
      ]. The lower BMC and BMD were unrelated to calcium intake [
      • Parsons T.J.
      • van Dusseldorp M.
      • van der Vliet M.
      • van de Werken K.
      • Schaafsma G.
      • van Staveren W.A.
      Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life.
      ]. In a later examination of the same cohort, most of whom had switched to a vegetarian or even OMN diet, low BMD and BMC were associated with B12 deficiency (low serum vitamin B12 or high methylmalonic acid) [
      • Dhonukshe-Rutten R.A.
      • van Dusseldorp M.
      • Schneede J.
      • de Groot L.C.
      • van Staveren W.A.
      Low bone mineral density and bone mineral content are associated with low cobalamin status in adolescents.
      ].

      Adults

      Numerous studies on calcium have been conducted on adult vegetarians worldwide. Most [
      • Yen C.E.
      • Yen C.H.
      • Huang M.C.
      • Cheng C.H.
      • Huang Y.C.
      Dietary intake and nutritional status of vegetarian and omnivorous preschool children and their parents in Taiwan.
      ,
      • Leblanc J.C.
      • Yoon H.
      • Kombadjian A.
      • Verger P.
      Nutritional intakes of vegetarian populations in France.
      ,
      • Lamberg-Allardt C.
      • Karkkainen M.
      • Seppanen R.
      • Bistrom H.
      Low serum 25-hydroxyvitamin D concentrations and secondary hyperparathyroidism in middle-aged white strict vegetarians.
      ,
      • Appleby P.
      • Roddam A.
      • Allen N.
      • Key T.
      Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford.
      ,
      • Davey G.K.
      • Spencer E.A.
      • Appleby P.N.
      • Allen N.E.
      • Knox K.H.
      • Key T.J.
      EPIC-Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33 883 meat-eaters and 31 546 non meat-eaters in the UK.
      ,
      • Janelle K.C.
      • Barr S.I.
      Nutrient intakes and eating behavior scores of vegetarian and nonvegetarian women.
      ,
      • Outila T.A.
      • Lamberg-Allardt C.J.
      Ergocalciferol supplementation may positively affect lumbar spine bone mineral density of vegans.
      ,
      • Cade J.E.
      • Burley V.J.
      • Greenwood D.C.
      The UK women's cohort study: comparison of vegetarians, fish-eaters and meat-eaters.
      ,
      • Lloyd T.
      • Schaeffer J.M.
      • Walker M.A.
      • Demers L.M.
      Urinary hormonal concentrations and spinal bone densities of premenopausal vegetarian and nonvegetarian women.
      ,
      • Tesar R.
      • Notelovitz M.
      • Shim E.
      • Kauwell G.
      • Brown J.
      Axial and peripheral bone density and nutrient intakes of postmenopausal vegetarian and omnivorous women.
      ] found that calcium intake in vegetarians (LOV, LV, LOV + VEG) did not differ from that in OMN. However in two studies [
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ,
      • Nakamoto K.
      • Watanabe S.
      • Kudo H.
      • Tanaka A.
      Nutritional characteristics of middle-aged Japanese vegetarians.
      ], calcium intake was higher in vegetarians, and in another [
      • Chiu J.F.
      • Lan S.J.
      • Yang C.Y.
      • Wang P.W.
      • Yao W.J.
      • Su L.H.
      • et al.
      Long-term vegetarian diet and bone mineral density in postmenopausal Taiwanese women.
      ] calcium intake was lower, but did not correlate with BMD. No significant difference in risk of fracture between vegetarians and OMN was reported after 5.2 years of follow up in one study [
      • Appleby P.
      • Roddam A.
      • Allen N.
      • Key T.
      Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford.
      ]. Other studies have reported no difference in BMD between vegetarians and OMN [
      • Krivosikova Z.
      • Krajcovicova-Kudlackova M.
      • Spustova V.
      • Stefikova K.
      • Valachovicova M.
      • Blazicek P.
      • et al.
      The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet.
      ,
      • Outila T.A.
      • Lamberg-Allardt C.J.
      Ergocalciferol supplementation may positively affect lumbar spine bone mineral density of vegans.
      ,
      • Lloyd T.
      • Schaeffer J.M.
      • Walker M.A.
      • Demers L.M.
      Urinary hormonal concentrations and spinal bone densities of premenopausal vegetarian and nonvegetarian women.
      ,
      • Tesar R.
      • Notelovitz M.
      • Shim E.
      • Kauwell G.
      • Brown J.
      Axial and peripheral bone density and nutrient intakes of postmenopausal vegetarian and omnivorous women.
      ]. However, a study on Taiwanese vegetarian women found that long-term VEG were at increased risk of lumbar spine fracture and femoral neck osteopenia compared to other long-term vegetarians. These differences were attributed to lower protein intake in VEG; calcium intake did not differ [
      • Chiu J.F.
      • Lan S.J.
      • Yang C.Y.
      • Wang P.W.
      • Yao W.J.
      • Su L.H.
      • et al.
      Long-term vegetarian diet and bone mineral density in postmenopausal Taiwanese women.
      ].
      A prospective year-long study on pre-menopausal women found that vegetarian women tended to have lower (but stable) BMD than non-vegetarians over the year [
      • Barr S.I.
      • Rideout C.A.
      Nutritional considerations for vegetarian athletes.
      ,
      • Barr S.I.
      • Prior J.C.
      • Janelle K.C.
      • Lentle B.C.
      Spinal bone mineral density in premenopausal vegetarian and nonvegetarian women: cross-sectional and prospective comparisons.
      ]; furthermore BMD at recruitment correlated significantly with vitamin B12 intake [
      • Barr S.I.
      • Rideout C.A.
      Nutritional considerations for vegetarian athletes.
      ,
      • Barr S.I.
      • Prior J.C.
      • Janelle K.C.
      • Lentle B.C.
      Spinal bone mineral density in premenopausal vegetarian and nonvegetarian women: cross-sectional and prospective comparisons.
      ]. A study on 122 Germans (35 OMN, 23 VEG and 54 LV/LOV) and 73 Indian immigrants to Oman (54 OMN, 19 LV/LOV) [
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ] found increased bone turnover (as measured by alkaline phosphatase, osteocalcin, pro-collagen type I N-terminal peptide and C-terminal telopeptides of collagen I) in vegetarians (LOV + VEG). Multiple regression analysis showed a significant association between increased bone turnover and vitamin B12 status that was independent of vitamin D status [
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ]. Finally, in a study on Indian and Iranian postmenopausal women, a pure vegetarian diet was a risk factor for osteoporosis among Indian women only, but this was not significant after adjustment for weight and height [
      • Keramat A.
      • Patwardhan B.
      • Larijani B.
      • Chopra A.
      • Mithal A.
      • Chakravarty D.
      • et al.
      The assessment of osteoporosis risk factors in Iranian women compared with Indian women.
      ]. From the studies reviewed above we conclude that in adult vegetarians, at-risk bone status correlates with long duration vegetarianism, low protein intake [
      • Chiu J.F.
      • Lan S.J.
      • Yang C.Y.
      • Wang P.W.
      • Yao W.J.
      • Su L.H.
      • et al.
      Long-term vegetarian diet and bone mineral density in postmenopausal Taiwanese women.
      ], and low vitamin B12 status [
      • Herrmann W.
      • Obeid R.
      • Schorr H.
      • Hubner U.
      • Geisel J.
      • Sand-Hill M.
      • et al.
      Enhanced bone metabolism in vegetarians – the role of vitamin B12 deficiency.
      ,
      • Krivosikova Z.
      • Krajcovicova-Kudlackova M.
      • Spustova V.
      • Stefikova K.
      • Valachovicova M.
      • Blazicek P.
      • et al.
      The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet.
      ,
      • Barr S.I.
      • Prior J.C.
      • Janelle K.C.
      • Lentle B.C.
      Spinal bone mineral density in premenopausal vegetarian and nonvegetarian women: cross-sectional and prospective comparisons.
      ].
      All studies [
      • Lamberg-Allardt C.
      • Karkkainen M.
      • Seppanen R.
      • Bistrom H.
      Low serum 25-hydroxyvitamin D concentrations and secondary hyperparathyroidism in middle-aged white strict vegetarians.
      ,
      • Appleby P.
      • Roddam A.
      • Allen N.
      • Key T.
      Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford.
      ,
      • Davey G.K.
      • Spencer E.A.
      • Appleby P.N.
      • Allen N.E.
      • Knox K.H.
      • Key T.J.
      EPIC-Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33 883 meat-eaters and 31 546 non meat-eaters in the UK.
      ,
      • Janelle K.C.
      • Barr S.I.
      Nutrient intakes and eating behavior scores of vegetarian and nonvegetarian women.
      ,
      • Chiu J.F.
      • Lan S.J.
      • Yang C.Y.
      • Wang P.W.
      • Yao W.J.
      • Su L.H.
      • et al.
      Long-term vegetarian diet and bone mineral density in postmenopausal Taiwanese women.
      ,
      • Ho-Pham L.T.
      • Nguyen P.L.
      • Le T.T.
      • Doan T.A.
      • Tran N.T.
      • Le T.A.
      • et al.
      Veganism, bone mineral density, and body composition: a study in Buddhist nuns.
      ,
      • Ho-Pham L.T.
      • Vu B.Q.
      • Lai T.Q.
      • Nguyen N.D.
      • Nguyen T.V.
      Vegetarianism, bone loss, fracture and vitamin D: a longitudinal study in Asian vegans and non-vegans.
      ,
      • Lightowler H.J.
      • Davies G.J.
      Micronutrient intakes in a group of UK vegans and the contribution of self-selected dietary supplements.
      ,
      • Outila T.A.
      • Karkkainen M.U.
      • Seppanen R.H.
      • Lamberg-Allardt C.J.
      Dietary intake of vitamin D in premenopausal, healthy vegans was insufficient to maintain concentrations of serum 25-hydroxyvitamin D and intact parathyroid hormone within normal ranges during the winter in Finland.
      ,
      • Strohle A.
      • Waldmann A.
      • Koschizke J.
      • Leitzmann C.
      • Hahn A.
      Diet-dependent net endogenous acid load of vegan diets in relation to food groups and bone health-related nutrients: results from the German Vegan Study.
      ,
      • Waldmann A.
      • Koschizke J.W.
      • Leitzmann C.
      • Hahn A.
      Dietary intakes and lifestyle factors of a vegan population in Germany: results from the German Vegan Study.
      ] found lower calcium intake in VEG than controls. A study that compared meat eaters, fish eaters, vegetarians and VEG found a higher fracture rate in VEG apparently related to markedly lower mean calcium intake [
      • Appleby P.
      • Roddam A.
      • Allen N.
      • Key T.
      Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford.
      ]. A study on VEG Buddhist nuns found lower calcium intake, but no differences in BMD, fracture incidence, or frequency of osteoporosis compared to non-VEG [
      • Ho-Pham L.T.
      • Nguyen P.L.
      • Le T.T.
      • Doan T.A.
      • Tran N.T.
      • Le T.A.
      • et al.
      Veganism, bone mineral density, and body composition: a study in Buddhist nuns.
      ,
      • Ho-Pham L.T.
      • Vu B.Q.
      • Lai T.Q.
      • Nguyen N.D.
      • Nguyen T.V.
      Vegetarianism, bone loss, fracture and vitamin D: a longitudinal study in Asian vegans and non-vegans.
      ]. Another study [
      • Outila T.A.
      • Lamberg-Allardt C.J.
      Ergocalciferol supplementation may positively affect lumbar spine bone mineral density of vegans.
      ] found no difference in BMD (measured in lumbar spine and femoral neck) between VEG, LOV and OMN.
      A study that compared 17 macrobiotic adults with VEG and LOV, found significantly lower calcium intake in the macrobiotic women than the other vegetarian groups [
      • Leblanc J.C.
      • Yoon H.
      • Kombadjian A.
      • Verger P.
      Nutritional intakes of vegetarian populations in France.
      ]. A study on 18 raw foodists in comparison with those eating typical American diets [
      • Fontana L.
      • Shew J.L.
      • Holloszy J.O.
      • Villareal D.T.
      Low bone mass in subjects on a long-term raw vegetarian diet.
      ] found that the raw foodists had significantly lower BMC and BMD than controls, with no differences in blood markers of bone turnover (C-telopeptide of type I collagen and bone-specific alkaline phosphatase).

      Elderly

      Elderly persons were included with adults in most of the studies reported above. We identified 2 studies conducted specifically on elderly women [
      • Lau E.M.
      • Kwok T.
      • Woo J.
      • Ho S.C.
      Bone mineral density in Chinese elderly female vegetarians, vegans, lacto-vegetarians and omnivores.
      ,
      • Reed J.A.
      • Anderson J.J.
      • Tylavsky F.A.
      • Gallagher Jr., P.N.
      Comparative changes in radial-bone density of elderly female lacto-ovovegetarians and omnivores.
      ]. The first [
      • Lau E.M.
      • Kwok T.
      • Woo J.
      • Ho S.C.
      Bone mineral density in Chinese elderly female vegetarians, vegans, lacto-vegetarians and omnivores.
      ] on elderly Chinese female VEG, LV and OMN found that among the women vegetarian for over 30 years (36 VEG; 40 LV) mean calcium intake was significantly lower than in OMN, and was also significantly lower in VEG than LV. BMD at the femoral neck, but not at the spine, was lower in vegetarians than OMN. The second [
      • Reed J.A.
      • Anderson J.J.
      • Tylavsky F.A.
      • Gallagher Jr., P.N.
      Comparative changes in radial-bone density of elderly female lacto-ovovegetarians and omnivores.
      ] was a prospective study on elderly white women (49 LOV, 140 OMN). The rate of loss of bone density over the five-year period, at each measurement site, was independent of calcium intake and was similar in both groups.

      Intervention studies

      Changes in nutritional status were evaluated during intervention studies with plant-based diets in healthy persons (Complete Health Improvement Project) [
      • Merrill R.M.
      • Aldana S.G.
      Consequences of a plant-based diet with low dairy consumption on intake of bone-relevant nutrients.
      ] or low-fat VEG diets (about 10% of total energy) in diabetic [
      • Turner-McGrievy G.M.
      • Barnard N.D.
      • Cohen J.
      • Jenkins D.J.
      • Gloede L.
      • Green A.A.
      Changes in nutrient intake and dietary quality among participants with type 2 diabetes following a low-fat vegan diet or a conventional diabetes diet for 22 weeks.
      ] and in prostate cancer patients [
      • Dunn-Emke S.R.
      • Weidner G.
      • Pettengill E.B.
      • Marlin R.O.
      • Chi C.
      • Ornish D.M.
      Nutrient adequacy of a very low-fat vegan diet.
      ]. During the intervention period, reduced calcium and vitamin D intake [
      • Merrill R.M.
      • Aldana S.G.
      Consequences of a plant-based diet with low dairy consumption on intake of bone-relevant nutrients.
      ] and lower vitamin D blood levels were observed [
      • Merrill R.M.
      • Aldana S.G.
      Consequences of a plant-based diet with low dairy consumption on intake of bone-relevant nutrients.
      ]. A short-term study evaluated calcium balance in women who received a VEG diet during the first 10 days, and a LV diet during the following 10 days: calcium balance remained positive regardless of intake. This finding indicates that the lower calcium intake of the VEG diet was compensated for by reduced calcium excretion in faeces. The two diets were not associated with differences in calcium balance, apparent absorption, or bone calcium resorption (assessed by a urine marker) [
      • Kohlenberg-Mueller K.
      • Raschka L.
      Calcium balance in young adults on a vegan and lactovegetarian diet.
      ].

      Recommendations

      Vegetarians should be urged to make sure they adopt a diet that ensures their calcium intake is in line with Italian recommendations [
      • SINU
      Intake levels of reference of nutrients and energy-IV revision.
      ]. VEG especially should be urged to regularly consume foods that are good sources of calcium (vegetables low in oxalate and phytate, soy products, calcium-rich mineral water, and various nuts and seeds).

      Iron

      Sources and bioavailability

      The bioavailability of iron in LOV, VEG and also OMN diets varies markedly. The main source of dietary iron in Italian OMN is cereals and cereal products (31.3%), followed by meat and meat products (16.9%), fresh and processed vegetables (13.5%), fruit (7.3%), pulses (3.2%), and potatoes and other tubers (3%) [
      • Sette S.
      • Le Donne C.
      • Piccinelli R.
      • Mistura L.
      • Ferrari M.
      • Leclercq C.
      The Third National Food Consumption Survey, INRAN-SCAI 2005–06: major dietary sources of nutrients in Italy.
      ]. Thus Italian OMN obtain close to 60% of their iron from plant sources.
      The typical Italian LOV and VEG diet may contain as much or more iron than an OMN diet, however iron bioavailability is lower [
      • Craig W.J.
      Nutrition concerns and health effects of vegetarian diets.
      ,
      • Hunt J.R.
      Bioavailability of iron, zinc, and other trace minerals from vegetarian diets.
      ] with only 5–12% absorbed, compared to 14–18% from OMN diets [
      • Hurrell R.
      • Egli I.
      Iron bioavailability and dietary reference values.
      ]. Non-haem iron provides 100% the iron of VEG and LOV diets, but only 85–90% of iron in OMN diets [
      • Hurrell R.
      • Egli I.
      Iron bioavailability and dietary reference values.
      ]. Much of the iron in soybeans is bound to ferritin and 22–34% of this is absorbed – a bioavailability comparable to that of haem iron (15–35%) [
      • Lonnerdal B.
      Soybean ferritin: implications for iron status of vegetarians.
      ,
      • Lonnerdal B.
      • Bryant A.
      • Liu X.
      • Theil E.C.
      Iron absorption from soybean ferritin in nonanemic women.
      ,
      • Agarwal U.
      Rethinking red meat as a prevention strategy for iron deficiency.
      ,
      • Theil E.C.
      • Briat J.
      Plant ferritin and non-heme iron nutrition in humans.
      ].
      Ascorbic acid, which chelates and reduces Fe3+, is the most important facilitator of non-haem iron absorption. Thus the bioavailability of iron in a vegetarian diet can be enhanced by consuming ascorbic acid (citrus fruits, strawberries, kiwi, etc.) during a meal containing iron [
      • Hunt J.R.
      • Roughead Z.K.
      Adaptation of iron absorption in men consuming diets with high or low iron bioavailability.
      ]. Other organic acids in fruits and vegetables (citric, malic, lactic and tartaric acids), as well as carotenes and retinol, also enhance non-haem iron absorption [
      • Craig W.J.
      Iron status of vegetarians.
      ,
      • Collings R.
      • Harvey L.J.
      • Hooper L.
      • Hurst R.
      • Brown T.J.
      • Ansett J.
      • et al.
      The absorption of iron from whole diets: a systematic review.
      ,
      • Garcia-Casal M.N.
      • Layrisse M.
      • Solano L.
      • Baron M.A.
      • Arguello F.
      • Llovera D.
      • et al.
      Vitamin A and beta-carotene can improve nonheme iron absorption from rice, wheat and corn by humans.
      ].
      Soaking pulses and cereal grains activates endogenous phytases that reduce the number of phosphates bound to inositol hexaphosphate (phytate) progressively weakening its ability to sequester iron. Use of the sour-dough method to leaven dough also activates phytases in the flour, again reducing the ability of phytate to sequester iron.
      Limited data indicate that the absorption of non-haem iron can increase over the long term in response low iron bioavailability [
      • Hunt J.R.
      • Roughead Z.K.
      Adaptation of iron absorption in men consuming diets with high or low iron bioavailability.
      ] which might explain why the prevalence of iron deficiency is similar in LOV, VEG and OMN [
      • Craig W.J.
      Nutrition concerns and health effects of vegetarian diets.
      ].

      Nutritional status of vegetarians at different ages

      The main tests on plasma or serum used to investigate iron nutritional status [
      • SINU
      Intake levels of reference of nutrients and energy-IV revision.
      ] are haemoglobin (to detect anaemia), transferrin saturation (measure of circulating iron), soluble transferrin receptor (more stable marker of iron levels in inflammation) and ferritin (indicator of iron storage). Since ferritin is also an inflammation marker, reactive protein C should also be determined.

      Breastfeeding women and preschool children (6 months to 3 years)

      The milk of LOV and VEG women is similar in composition to milk from non-vegetarian women [
      • Craig W.J.
      • Mangels A.R.
      Position of the American Dietetic association: vegetarian diets.
      ] and is not deficient in minerals or vitamins when the maternal LOV/VEG diet is well-balanced [
      Vegetarian weaning. Nutrition Standing Committee of the British Paediatric Association.
      ]. When the children of vegetarian mothers are weaned their iron status should be monitored, and iron-rich foods should be eaten together with food containing ascorbic acid or other fruit acids so as to improve iron absorption [
      Vegetarian weaning. Nutrition Standing Committee of the British Paediatric Association.
      ].
      The incidence of iron deficiency anaemia during weaning is not higher in LOV/VEG children than OMN children, and serum ferritin levels (and growth) are usually within normal ranges in LOV/VEG children [
      • Agarwal U.
      Rethinking red meat as a prevention strategy for iron deficiency.
      ].

      Children (4–10 years)

      LOV and VEG children have lower iron intakes than OMN children but their serum iron levels are within the normal range [
      • Laskowska-Klita T.
      • Chelchowska M.
      • Ambroszkiewicz J.
      • Gajewska J.
      • Klemarczyk W.
      The effect of vegetarian diet on selected essential nutrients in children.
      ] and do not differ significantly from those of OMN children [
      • Craig W.J.
      Iron status of vegetarians.
      ]. Pre-school and school-age VEG have adequate iron intake and anaemia has not been documented [
      • Sanders T.A.
      Growth and development of British vegan children.
      ,
      • Fulton J.R.
      • Hutton C.W.
      • Stitt K.R.
      Preschool vegetarian children. Dietary and anthropometric data.
      ]. However, the Institute of Medicine [
      • Institute of Medicine
      Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc.
      ], suggests that LOV/VEG children should consume 1.8 times more iron than OMN children, to ensure their nutritional needs are met. Macrobiotic children also often have low iron status [
      • Craig W.J.
      Iron status of vegetarians.
      ].

      Adolescents (11–18 years)

      The development of LOV and VEG teenagers is similar to that of non-vegetarian teenagers [
      • Craig W.J.
      • Mangels A.R.
      Position of the American Dietetic association: vegetarian diets.
      ]. Slovak LOV and LV children aged 11–14 years had lower serum iron and haemoglobin than OMN but levels were within the normal range [
      • Krajcovicova-Kudlackova M.
      • Simoncic R.
      • Bederova A.
      • Grancicova E.
      • Magalova T.
      Influence of vegetarian and mixed nutrition on selected haematological and biochemical parameters in children.
      ]. However to meet iron needs in this period of rapid growth, LOV/VEG teenagers should consider iron supplementation [
      • Donovan U.M.
      • Gibson R.S.
      Iron and zinc status of young women aged 14 to 19 years consuming vegetarian and omnivorous diets.
      ]. In a Swedish study [
      • Larsson C.L.
      • Johansson G.K.
      Dietary intake and nutritional status of young vegans and omnivores in Sweden.
      ] the iron intake of adolescent (16–20 years) VEG (at least 6 months) of both sexes was compared with that of OMN. Iron intake in VEG and OMN males was similar. VEG females consumed more iron than OMN females and the population reference intake (PRI); in all cases iron intake was within the recommended range. However serum iron markers were lower than normal in VEG and OMN females but normal in VEG and OMN males, indicating that menstrual blood loss was responsible for the lower iron levels and that diet had no influence.

      Adults

      Even after many years on a LOV or VEG diet, serum iron levels in adults do not usually differ significantly from those in OMN [
      • Craig W.J.
      Iron status of vegetarians.
      ]. Mean iron intake in LOV/VEG men can in fact be higher than in OMN men, and also higher than the PRI [
      • Wilson A.K.
      • Ball M.J.
      Nutrient intake and iron status of Australian male vegetarians.
      ]. Nevertheless serum ferritin and haemoglobin are significantly lower in LOV and VEG males than OMN controls [
      • Haddad E.H.
      • Berk L.S.
      • Kettering J.D.
      • Hubbard R.W.
      • Peters W.R.
      Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians.
      ,
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ,
      • Nakamoto K.
      • Watanabe S.
      • Kudo H.
      • Tanaka A.
      Nutritional characteristics of middle-aged Japanese vegetarians.
      ,
      • Huang Y.C.
      • Lin W.J.
      • Cheng C.H.
      • Su K.H.
      Nutrient intakes and iron status of healthy young vegetarians and non vegetarians.
      ]. LOV/VEG women also have a similar iron intake to OMN controls [
      • Anderson B.M.
      • Gibson R.S.
      • Sabry J.H.
      The iron and zinc status of long-term vegetarian women.
      ] and after many years on a vegetarian diet their iron status is adequate [
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ,
      • Anderson B.M.
      • Gibson R.S.
      • Sabry J.H.
      The iron and zinc status of long-term vegetarian women.
      ,
      • Ball M.J.
      • Bartlett M.A.
      Dietary intake and iron status of Australian vegetarian women.
      ]. Nevertheless, the risk of iron anaemia is reported to be about 40% in pre-menopausal women after one year on a VEG diet [
      • Waldmann A.
      • Koschizke J.W.
      • Leitzmann C.
      • Hahn A.
      Homocysteine and cobalamin status in German vegans.
      ,
      • Haddad E.H.
      • Berk L.S.
      • Kettering J.D.
      • Hubbard R.W.
      • Peters W.R.
      Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians.
      ]. Haddad et al. [
      • Haddad E.H.
      • Berk L.S.
      • Kettering J.D.
      • Hubbard R.W.
      • Peters W.R.
      Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians.
      ] found that pre-menopausal VEG and OMN women had similar risks of developing iron anaemia. Studies on young females [
      • Huang Y.C.
      • Lin W.J.
      • Cheng C.H.
      • Su K.H.
      Nutrient intakes and iron status of healthy young vegetarians and non vegetarians.
      ,
      • Harvey L.J.
      • Armah C.N.
      • Dainty J.R.
      • Foxall R.J.
      • John L.D.
      • Langford N.J.
      • et al.
      Impact of menstrual blood loss and diet on iron deficiency among women in the UK.
      ] also show that iron deficiency anaemia is present at similar levels in LOV and VEG (at least two years) and OMN. Thus menstrual iron loss rather than diet appears as the main cause of iron deficiency anaemia. In postmenopausal women, high blood ferritin has been found to be a risk factor for cardiovascular diseases [
      • Hanson L.N.
      • Engelman H.M.
      • Alekel D.L.
      • Schalinske K.L.
      • Kohut M.L.
      • Reddy M.B.
      Effects of soy isoflavones and phytate on homocysteine, C-reactive protein, and iron status in postmenopausal women.
      ], so LOV and VEG diets may be protective against these conditions.
      Nevertheless iron and vitamin B12 status can both be compromised in adult LOV, LV, and occasional meat eaters; in such cases macrocytosis due to B12 deficiency can be masked by low iron status [
      • Obeid R.
      • Geisel J.
      • Schorr H.
      • Hubner U.
      • Herrmann W.
      The impact of vegetarianism on some haematological parameters.
      ].

      Elderly

      A study that investigated the adequacy of LOV and VEG diets in elderly persons [
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ] found that mean daily mineral intake, iron included, and iron serum markers were within normal ranges [
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ] and did not differ significantly from OMN controls. In older men (59–78 years) undergoing 12 weeks of resistance training designed to maintain muscle mass, serum iron remained within normal limits throughout the training period, irrespective of whether they ate a beef-containing or vegetarian diet [
      • Wells A.M.
      • Haub M.D.
      • Fluckey J.
      • Williams D.K.
      • Chernoff R.
      • Campbell W.W.
      Comparisons of vegetarian and beef-containing diets on hematological indexes and iron stores during a period of resistive training in older men.
      ]. These findings suggest that a vegetarian diet is suitable for elderly persons [
      • Deriemaeker P.
      • Alewaeters K.
      • Hebbelinck M.
      • Lefevre J.
      • Philippaerts R.
      • Clarys P.
      Nutritional status of Flemish vegetarians compared with non-vegetarians: a matched samples study.
      ,
      • Wells A.M.
      • Haub M.D.
      • Fluckey J.
      • Williams D.K.
      • Chernoff R.
      • Campbell W.W.
      Comparisons of vegetarian and beef-containing diets on hematological indexes and iron stores during a period of resistive training in older men.
      ].

      Recommendations

      Vegetarians should be advised increase iron intake above the PRI suggested for OMN, by eating a variety of iron-rich plant foods. Iron bioavailability can be increased by:
      • 1.
        Eating ascorbic acid-rich foods together with iron-rich foods.
      • 2.
        Using food preparation methods such as grinding, soaking and germination, and using the sour-dough method to leaven bread (or buy sour-dough bread). These processes lower the phytic acid content of cereals and legumes and thus reduce iron sequestration.
      • 3.
        Using iron-fortified foods (e.g. breakfast cereals).
      Iron supplementation is only recommended if iron status has been shown to be low by appropriate blood tests.

      Zinc

      Sources and bioavailability

      According to the US Department of Agriculture (reported in Hunt [
      • Hunt J.R.
      Moving toward a plant-based diet: are iron and zinc at risk?.
      ]) over half the zinc in OMN diets (56%) comes from animal origin foods. Similarly, a 2013 Italian food survey [
      • Sette S.
      • Le Donne C.
      • Piccinelli R.
      • Mistura L.
      • Ferrari M.
      • Leclercq C.
      The Third National Food Consumption Survey, INRAN-SCAI 2005–06: major dietary sources of nutrients in Italy.
      ] reported that 54.9% of the dietary zinc of Italians comes from animal products (24.8% meat and meat products, 21% milk and milk products, 6.9% fish, seafood and their products, 2.2% eggs), and 40.7% from plant foods (21.5% cereals and cereal products, 9.8% vegetables, 5.5% potatoes and other tubers, 2.8% fruits, 1.1% pulses), with sweet products, water and non-alcoholic beverages providing minimal amounts.
      Good zinc sources for VEG and LOV are whole grains, cereals, pulses, nuts and seeds [
      • Venti C.A.
      • Johnston C.S.
      Modified food guide pyramid for lactovegetarians and vegans.
      ]. However, these foods are also rich in phytate which is a strong zinc chelating agent that severely limits intestinal absorption. Oxalate and some dietary fibres also decrease zinc absorption [
      • Gibson R.S.
      Content and bioavailability of trace elements in vegetarian diets.
      ,
      • Lonnerdal B.
      Dietary factors influencing zinc absorption.
      ].
      Zinc absorption from VEG/LOV diets is 15–26%, while that from typical OMN diets is 33–35% [
      • Gibson R.S.
      Content and bioavailability of trace elements in vegetarian diets.
      ,
      • Hunt J.R.
      • Matthys L.A.
      • Johnson L.K.
      Zinc absorption, mineral balance, and blood lipids in women consuming controlled lactoovovegetarian and omnivorous diets for 8 wk.
      ]. The consumption of small quantities of animal proteins considerably enhances zinc absorption [
      • Sandstrom B.
      • Arvidsson B.
      • Cederblad A.
      • Bjorn-Rasmussen E.
      Zinc absorption from composite meals. I. The significance of wheat extraction rate, zinc, calcium, and protein content in meals based on bread.
      ], perhaps due to the release of amino acids during digestion which keep zinc in solution (prevent its chelation) [
      • Lonnerdal B.
      Dietary factors influencing zinc absorption.
      ]. Sulphur amino acids, cysteine-containing peptides, hydroxy acids (present in fruits) and other organic acids present in fermented food may all increase zinc absorption [
      • Sandstrom B.
      • Arvidsson B.
      • Cederblad A.
      • Bjorn-Rasmussen E.
      Zinc absorption from composite meals. I. The significance of wheat extraction rate, zinc, calcium, and protein content in meals based on bread.
      ,
      • Wegmuller R.
      • Tay F.
      • Zeder C.
      • Brnic M.
      • Hurrell R.F.
      Zinc absorption by young adults from supplemental zinc citrate is comparable with that from zinc gluconate and higher than from zinc oxide.
      ]. As with iron, procedures that activate the endogenous phytases present in cereals and pulses, like milling, sprouting, soaking, and sour-dough leavening, increase the bioavailability of zinc [
      • Craig W.J.
      Nutrition concerns and health effects of vegetarian diets.
      ,
      • Chiplonkar S.A.
      • Agte V.V.
      Predicting bioavailable zinc from lower phytate forms, folic acid and their interactions with zinc in vegetarian meals.
      ].

      Nutritional status of vegetarians at different ages

      Because of zinc's protein biochemical roles, various signs of zinc deficiency may manifest that also depend on the severity of the deficiency; for the same reason it is difficult to identify reliable biomarkers of zinc status [
      • King J.C.
      Zinc: an essential but elusive nutrient.
      ,
      • Gibson R.S.
      • Hess S.Y.
      • Hotz C.
      • Brown K.H.
      Indicators of zinc status at the population level: a review of the evidence.
      ]. Markers considered useful for assessing zinc nutritional status are plasma levels [
      • Lowe N.M.
      • Fekete K.
      • Decsi T.
      Methods of assessment of zinc status in humans: a systematic review.
      ], serum levels [
      • Roohani N.
      • Hurrell R.
      • Kelishadi R.
      • Schulin R.
      Zinc and its importance for human health: an integrative review.
      ] and urinary excretion [
      • Lowe N.M.
      • Fekete K.
      • Decsi T.
      Methods of assessment of zinc status in humans: a systematic review.
      ].

      Breastfeeding women and preschool children (6 months to 3 years)

      If breast-feeding LOV/VEG mothers have adequate zinc intake, the zinc nutritional status of their infants does not differ from that of breast-fed infants of OMN mothers [
      Vegetarian weaning. Nutrition Standing Committee of the British Paediatric Association.
      ]. When breast-feeding is not possible or insufficient [
      • Casey C.E.
      • Neville M.C.
      • Hambidge K.M.
      Studies in human lactation: secretion of zinc, copper, and manganese in human milk.
      ], adequate zinc intake for LOV infants can be provided by modified cow milk formula, and soy or rice preparations [
      • Lasekan J.B.
      • Ostrom K.M.
      • Jacobs J.R.
      • Blatter M.M.
      • Ndife L.I.
      • Gooch III, W.M.
      • et al.
      Growth of newborn, term infants fed soy formulas for 1 year.
      ,
      Breastfeeding and the use of human milk.