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The majority of zinc in the Western diet comes together with animal proteins. Legumes, whole grains, nuts, and seeds are reasonable plant-substitute sources of zinc. However, the bioavailability of zinc is reduced by high levels of supplemental calcium and by phytate, which is also found in legumes, whole grains, nuts, and seeds. Vegetarians and vegans appear to have adequate zinc status, but lower serum levels than nonvegetarian counterparts [30]. Little is known regarding the effects of marginal zinc deficiency. Although adaptation to a low intake may occur over time, thanks to increased intestinal absorption [29], good plant sources of zinc, as shown in Table 20.2, should be encouraged.

Vitamin B12 (Cobalamin)

Vitamin B12 is required by the body in microgram amounts and is found only in food of animal origin. Deficiency of this vitamin is extremely rare as the human body stores several years’ worth of it. Elderly and strict vegan individuals are most at risk. Deficiency of B12 can cause pernicious anemia and can result in megaloblastic anemia with central nervous system demyelination if not treated early. Symptoms in infants and children include irritability, failure to thrive, and feeding difficulties; prolonged deficiency can lead to permanent developmental disabilities [31, 32]. Diagnosing B12 deficiency prior to symptom development in vegetarians is difficult, usually due to a high folate intake masking the hematological signs of deficiency. Since folate intake is often higher in vegan diets, elevated serum methylmalonic acid, holo transcobalamin, and/or homocysteine may be more sensitive indicators of a B12 deficiency [32]. Purported plant-based sources (tempeh, algae extracts, and sea vegetables) have been found to contain more inactive corrinoids than true B12 [32] and thus they are not reliable sources of B12. Risk of B12 deficiency in vegans is increased if their diet is not supplemented with fortified products (fortified yeast extract, fortified soy products, and some brands of breakfast cereals). It is recommended that vegans include three dietary sources of B12 per day. If this is not achievable, a daily supplement of 5-10 pg is recommended for adults [26]. Supplementation of 25-100 pg/day has been used to maintain vitamin B12 levels in older people. Unless the maternal diet is adequate in B12, breastfed infants should receive 0.4 pg/day from birth to 6 months, and 0.5 pg/day after that time [23].

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