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Proteins from plant sources alone can provide enough amino acids if the diet is varied and meets energy needs. Research suggests that in healthy people who eat a vegan diet without supplemental protein, the amino acids consumed throughout the day from a variety of sources ensure adequate nitrogen retention and use in the body. Although the total protein content of a vegetarian diet is lower than that of a meat diet, and the lower quality of some plant proteins may raise the protein requirements of vegetarians, the protein intake of both dairy and egg vegetarians and complete vegetarians appears to be adequate.

Plant foods contain only non-ferroheme iron, which is more sensitive than ferroheme iron to inhibitory and fortifying factors that affect iron absorption. Because of the poor absorption of iron from plant foods by the body, vegetarians have lower iron stores in their bodies, even though vegetarian diets contain more iron than non-vegetarian diets. Since the prevalence of anemia is similar in vegetarians and non-vegetarians, it is not clear what the clinical significance of the low iron stock in vegetarians is. Vegetarian diets are high in vitamin C, which improves iron absorption.

While residual soil on the surface of plant foods can contain vitamin B-12, this is not a reliable source of B-12 for vegetarians. Vitamin B-12 provided by spirulina, sea plants, soybean fermented foods, and Japanese bean and noodle sauces are analogs of inactive B-12, not active vitamins. Although dairy products and eggs contain vitamin B-12, studies have shown that blood levels of vitamin B-12 are low in dairy and egg vegetarians. Vitamin B-12 supplements or fortified foods are recommended for vegetarians who avoid or restrict animal foods.

Because vitamin B-12 is not needed in large quantities and because it can be stored and reused in the body, the onset of symptoms of deficiency can be delayed for many years, so vitamin B-12 supplementation is recommended for all older vegetarians.

Lacto-ovo vegetarians have a calcium intake that is comparable to or higher than that of non-vegetarians. Complete vegetarians, on the other hand, have lower calcium intakes than both lacto-ovo vegetarians and omnivores. It should be noted that complete vegetarians may have lower calcium requirements due to the calcium-sparing effect of foods that are low in total protein and highly alkaline. In addition, a person who eats foods low in protein and sodium, combined with regular weight-bearing exercise, may have lower calcium requirements compared to a person who eats a standard Western diet and is habitually sedentary. These factors, combined with genetic influences, could explain differences in bone health that are not affected by calcium intake.

Any human being willing to abolish meat is better off without it, and for this vegetarian opinion I strongly endorse it.

--Dr. Michael McKay, John Hagin University of Medicine (nutrition authority)

Because the calcium needs of complete vegetarians have not been determined, and because the risk of osteoporosis in all women has been linked to insufficient calcium intake, complete vegetarians should have their calcium needs met in quantities determined by the Institute of Medicine on the basis of age. Calcium in many plant foods is well absorbed by the body, and a vegetarian diet can provide enough calcium when calcium-rich foods are often included in the diet. Also. Many of the newer vegan diets are fortified with calcium. Vegetarians need to take prescribed calcium-supplemented foods only if their food does not meet their calcium needs.

Unless one eats fortified foods fortified with vitamin D, the supply of vitamin D in all kinds of foods is inadequate. Since fortified milk is the most common food source of vitamin D, a complete vegan diet may be deficient in vitamin D. However, strict vegan diets, such as soy milk and some cereals, can also be used to supplement vitamin D. In addition, studies have found that sun exposure is the main factor affecting vitamin D levels, and that dietary sources of vitamin D are important only when sun exposure is inadequate. Studies have concluded that getting 5 to 15 minutes of sunlight on your hands, arms, and face each day can provide enough vitamin D (31). People with dark skin or those who live in northern latitudes or in cloudy, foggy areas may need more sun exposure. The use of shade can hinder vitamin D synthesis. The study suggests that vegetarians who don't get enough sun should take vitamin D supplements, which is especially important for older adults, who synthesize vitamin D less efficiently and may also get less sun.

Studies have shown that vegans have lower or comparable zinc intakes than non-vegans. Most studies show that zinc levels in hair, serum and saliva of vegetarians are in the normal range. Compensatory mechanisms may help vegetarians adapt to foods with low zinc levels (33). However, because of the low bioavailability of zinc from plants and because the marginal effects of changes in zinc levels are unknown, vegetarians should strive to meet or exceed the recommended dietary allowance of zinc.

Foods that do not include fish or eggs lack the long-chain n-3 fatty acid docosahexanoic acid (DHA). Vegetarians may have lower lipid levels of this fatty acid, although not so studies agree with this judgment. The essential fatty acid linolenic acid can be converted to DHA, although the conversion appears to be inefficient and is impeded by high linolenic acid intake. It's not clear what effect low DHA levels have. However, the study suggests that vegetarians should eat foods rich in linolenic acid.