While a well-planned, balanced vegan diet is suitable to meet all recommendations for nutrients in every stage of life, improperly-planned vegan diets may be deficient in vitamin B12, vitamin D, calcium, iodine, iron, zinc, riboflavin (vitamin B2), long-chain fatty acids EPA and DHA, and omega-3 fatty acids.
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. 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. 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.
Some athletes, such as Brendan Brazier, follow a vegan diet, including raw veganism. 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. 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.
The American Dietetic Association and Dietitians of Canada state that well-planned vegan diets can meet all nutrient requirements and are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence. Poorly planned vegan diets may be low in vitamin B12, omega-3 fatty acids, vitamin D, calcium, iron, zinc, riboflavin (vitamin B2), and iodine.
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. This is because, unless fortified, plant foods do not contain reliable amounts of active vitamin B12. Vegans are recommended to do one of the following dietary options:
- Consume fortified foods 2-3 times per day to get at least 3 micrograms of vitamin B12,
- or take 1 vitamin B12 supplement per day to get at least 10 micrograms
- or take 1 weekly B12 supplement to get a least 2000 micrograms.
Omega-3 fatty acids
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). 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. Short-term supplemental ALA has been shown to increase EPA levels but not DHA levels, suggesting poor conversion of the intermediary EPA to DHA. DHA supplements derived from DHA-rich microalgae are available, and the human body can also convert DHA to EPA.
There is only weak evidence that omega-3 benefits cardiovascular health, and although omega-3 has previously been thought useful for helping alleviate dementia, as of 2016 there is no good evidence of effectiveness.
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. 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.
It is recommended that vegans eat three servings per day of a high-calcium food, such as fortified soy milk, almonds, hazelnuts, kale, collard greens, Chinese greens, and take a calcium supplement or other calcium-fortified foods as necessary.
Many studies have examined possible correlation between veganism, calcium intake, and bone health. The EPIC-Oxford study suggested that vegans who consumed 525 mg or less of calcium per day have an increased risk of bone fractures over meat eaters and vegetarians, but that vegans consuming more than 525 mg/day had a risk of fractures similar to other groups. Overall, the entire group of vegans had a higher risk of fractures. A 2009 study of bone density found the bone density of vegans was 94 percent that of omnivores, but deemed the difference clinically insignificant. Another study in 2009 by the same researchers examined over 100 vegan post-menopausal women, and found that their diet had no adverse effect on bone mineral density (BMD) and no alteration in body composition. Biochemist T. Colin Campbell suggested in The China Study (2005) that osteoporosis is linked to the consumption of animal protein because, unlike plant protein, animal protein increases the acidity of blood and tissues, which is then neutralized by calcium pulled from the bones resulting in hypercalciuria. Campbell wrote that his China-Oxford-Cornell study of nutrition in the 1970s and 1980s found that, in rural China, "where the animal to plant ratio [for protein] was about 10 percent, the fracture rate is only one-fifth that of the U.S."
Calcium is one component of the most common type of human kidney stones, calcium oxalate. Some studies suggest that people who take supplemental calcium have a higher risk of developing kidney stones, and these findings have been used as the basis for setting the recommended daily intake (RDI) for calcium in adults.
One study reported a "potential danger of iodine deficiency disorders due to strict forms of vegetarian nutrition, especially when fruits and vegetables grown in soils with low [iodine] levels are ingested."
It is recommended for vegans to eat iron-rich foods and vitamin C daily. In several studies, vegans were not found to suffer from iron-deficiency any more than non-vegans. However, due to the low absorption rate on non-heme iron it is recommended to eat dark leafy greens (and other sources of iron) together with sources of Vitamin C.
It is recommended for vegans to eat food rich in choline, as plant based sources of choline are limited. Soy lecithin, cauliflower, spinach, wheat germ, firm tofu, kidney beans, quinoa and amaranth are vegan sources of choline. The Adequate Intake (AI) of choline is 425 mg (milligrams) per day for adult women; higher for pregnant and breastfeeding women. The AI for adult men is 550 mg/day. Choline deficiency can lead to health problems such as liver damage, a result of liver cells initiating programmed cell death (apoptosis), as well as an increase in neural tube defects in pregnant women. In a study, 77% of men, 44% of premenopausal women, and 80% of postmenopausal women developed fatty liver or muscle damage due to choline deficiency, showing that subject characteristics regulate the dietary requirement. Choline deficiency has also been associated with hypertension in rats. There is also some evidence that choline is an anti-inflammatory as well, but further studies are needed to confirm/refute findings. In order to avoid these problems, it's important to meet the adequate intake, especially since many multivitamins do not contain enough choline. Although many animal products, like liver and egg, contain high amounts of choline (355 mg/3 oz and 126 mg/large egg, respectively), wheat germ (172 mg/cup), brussel sprouts (63 mg/cup), and broccoli (62 mg/cup) are good sources of choline as well.
- For an overview, see:
- American Dietetic, Association; Dietitians Of, Canada (2003). "Position of the American Dietetic Association and Dietitians of Canada : Vegetarian Diets". Canadian Journal of Dietetic Practice and Research. 64 (2): 62–81. doi:10.3148/64.2.2003.62. PMID 12826028.
- Key, Timothy J.; Appleby, Paul N.; Rosell, Magdalena S. (2007). "Health effects of vegetarian and vegan diets". Proceedings of the Nutrition Society. 65 (1): 35–41. doi:10.1079/PNS2005481. PMID 16441942.
- For vitamin D and calcium: Appleby, P; Roddam, A; Allen, N; Key, T (2007). "Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford". European Journal of Clinical Nutrition. 61 (12): 1400–6. doi:10.1038/sj.ejcn.1602659. PMID 17299475.
- For iron: "Iron deficiency—adults". Better Health Channel. Government of Victoria, Australia. Retrieved February 4, 2011.
High-risk groups such as vegetarians, adolescent girls and women athletes need to eat iron-rich foods each day (combined with foods that are high in vitamin C). …Vegetarians who exclude all animal products from their diet may need almost twice as much dietary iron each day as non-vegetarians. Sources include dark green leafy vegetables—such as spinach—and raisins, nuts, seeds, beans, peas, and iron-fortified cereals, breads and pastas.
- Segelken, Roger (2001-06-28). "China Study II: Switch to Western diet may bring Western-type diseases". Cornell Chronicle. Retrieved 2006-09-15.
- "China-Cornell-Oxford Project On Nutrition, Environment and Health at Cornell University". Division of Nutritional Sciences. Cornell University. Retrieved 2006-09-15.
- Barnard, Neal D. (2007). Dr. Neal Barnard's Program for Reversing Diabetes. New York: Rodale. pp. 40–50.
Set aside animal products
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- "Despite the seeming hardships a vegan diet imposes on its practitioners, veganism is a burgeoning movement, especially among younger Americans. In the endurance sports, such as the Ironman triathlon and the Utramarathon, the top competitors are vegans who consume much of their vegan food in its uncooked state. Even young weight lifters and body builders are gravitating to a vegan diet, giving the lie to the notion that eating animal flesh is essential for strength and stamina. Brendan Brazier, a young athlete who regularly places in the top three in international triathlon events and who formulated Vega, a line of plant-based performance products, said of his fellow vegan athletes: 'We're beginning to build a strong presence in every sport.'"
- Also see Nijjar, Raman. "From pro athletes to CEOs and doughnut cravers, the rise of the vegan diet", CBC News, June 4, 2011.
- For other examples of Ironman triathlon athletes who are vegan, see Scott, David and Heidrich, Ruth. "Vegetarian/Vegan Ironman and Ironlady", European Vegetarian Union News, issue 4, 1997.
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The key role of ascorbic acid for the absorption of dietary nonheme iron is generally accepted. The reasons for its action are twofold: (1) the prevention of the formation of insoluble and unabsorbable iron compounds and (2) the reduction of ferric to ferrous iron, which seems to be a requirement for the uptake of iron into the mucosal cells.
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