Vegan nutrition refers to the nutritional aspects of vegan diets - diets which include no animal products.

Poorly planned vegan diets can be deficient in vitamin B12, vitamin D, calcium, iodine, iron, zinc, riboflavin (vitamin B2) and omega-3 fatty acids.[1]

Doctors Dean Ornish, T. Colin Campbell, John A. McDougall, Michael Klaper, Caldwell Esselstyn, Michael Greger, Joel Fuhrman, and Neal D. Barnard claim that high animal fat and protein diets, such as the standard American diet, are detrimental to health.[2][3][4] They also state that a lifestyle change incorporating a vegan whole foods diet could not only prevent various degenerative diseases, such as coronary artery disease, but reverse them.[5][6][7][8][9] A number of documentary films, such as Fat, Sick and Nearly Dead, Planeat and Forks over Knives, focus on the purported health benefits of plant-based diets. Although there is general consensus amongst doctors advocating plant-based diets, Joel Fuhrman and Michael Greger have disagreed with Campbell and Esselstyn on the use of nuts and seeds.[10]

Some top athletes, such as Brendan Brazier, follow a vegan diet, including raw veganism.[11] Vegan diets tend to be higher in dietary fibre, magnesium, folic acid, vitamin C, vitamin E, iron, and phytochemicals, and lower in calories, saturated fat, cholesterol, long-chain omega-3 fatty acids, vitamin D, calcium, zinc, and vitamin B12.[12] Because uncontaminated plant foods do not provide vitamin B12 (which is produced by microorganisms such as bacteria), researchers agree that vegans should eat foods fortified with B12 or take a daily supplement.[13]

Poorly planned vegan diets may be low in vitamin B12, omega-3 fatty acids, vitamin D, calcium, iron, zinc, riboflavin (vitamin B2), and iodine. The American Dietetic Association and Dietitians of Canada state that well-balanced vegan diets can meet all these nutrient requirements and are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence.[14]

Vitamin B12 deficiency is potentially extremely serious, leading to megaloblastic anemia, nerve degeneration and irreversible neurological damage. [15]

Evidence suggests that vegans who are not taking vitamin B12 supplements do not consume sufficient servings of B12 and often have abnormally low blood concentrations of vitamin B12.[16] This is because, unless fortified, plant foods do not contain reliable amounts of active vitamin B12.

Proteins are composed of amino acids and essential amino acids cannot be synthesised by the human body. A 1994 study found a varied intake of such sources can be adequate.[17] The source and composition of vegan proteins have been associated with a reduced risk in cancer and other comorbidities including cardiovascular disease.[18]

Vegan diets can be low in omega-3 fatty acids (O3FA). Major vegan sources of O3FA include algae, hempseeds and hempseed oil, walnuts, flaxseeds and flaxseed oil, olive oil, canola (rapeseed) oil, avocado and chia seeds. However, diets lacking generous amounts of sea vegetables (seaweed) generally lack a direct source of long-chain O3FA such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).[citation needed] Vegan diets, like the standard American diet, may also have a high ratio of O6FA to O3FA, which inhibits the conversion of short-chain fatty acids such as alpha-Linolenic acid (ALA), found in most vegan O3FA sources, to EPA and DHA.[1] Short-term supplemental ALA has been shown to increase EPA levels but not DHA levels, suggesting poor conversion of the intermediary EPA to DHA.[19] DHA supplements derived from DHA-rich microalgae are available,[1] and the human body can also convert DHA to EPA.[20]

While there is no scientific consensus on the role of omega-3 fatty acids, they may reduce the risk of coronary heart disease,[1] lower triglycerides, stabilize mood and help prevent depression, help reduce symptoms of ADD, reduce joint pain and other rheumatoid problems, and reduce the risk of dementia in older age.[citation needed] While there is little evidence of adverse health or cognitive effects due to DHA deficiency in adult vegetarians or vegans, fetal and breast milk levels remain a concern.[19] EPA and DHA supplementation has been shown to reduce platelet aggregation in vegetarians, but a direct link to cardiovascular morbidity and mortality, which is already lower for vegetarians, has yet to be determined.[21]

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Vegan nutrition - Wikipedia, the free encyclopedia