Vegan nutrition
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- For general information, see Veganism.
Vegan nutrition encompasses the nutrients vegans require for a balanced diet. It is an important part of a vegan's life, as it is the foundation for determining which foods should be consumed based on their lifestyle choices. Vegan nutrition usually refers to the intake and balance of nutrients throughout a day, and therefore is dually classified under dietary regimes and practices.
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[edit] Balance and regulation
A U.S. Dept of Agriculture (USDA) study found that vegan women may have a higher rate of bone formation than omnivorous women.[1]
[edit] Fatty acids
Omega-3 fatty acids can be obtained from vegan sources such as hempseed or canola (rapeseed) oils, as well as in walnuts, dark green leafy vegetables and ground flaxseed. [2] Flaxseed must be ground however, as whole seeds are not broken down in the intestines. Flaxseed oil, although it has omega-3, is unstable and temperature sensitive.
There are several vital omega-3 fatty acids. Most vegetable sources contain only alpha-linolenic acid (ALA). But the human body also requires eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The human body can convert ALA to EPA, and EPA to DHA, but the efficiency, and sufficiency for optimal health, of this conversion is controversial. Studies have found EPA and DHA levels in vegans to be about two thirds lower than in omnivorous people. In how far this may pose a health risk is not known, but vegans have been advised to increase their intake of alpha-linolenic acid, and reduce their intake of omega-6 fatty acids and saturated fatty acids, which can limit the rate of conversion. Recently, some companies have begun to market vegan DHA supplements containing seaweed extracts. Whole seaweeds are not suitable for supplementation because their high iodine content limits the amount that may be safely consumed.
The importance of Omega-3 was highlighted in the "Lyon Diet Heart Study",[1] which found deaths due to heart disease were much lower in a group which followed a Mediterranean diet in comparison to a group following the American Heart Association Diet. The difference between the groups was so large that the study was stopped early by an ethics committee, who found it unethical to continue with so fewer deaths in the Mediterranean group after just one year. The Mediterranean diet emphasizes bread, vegetables, fish, poultry and fruit.[3]
[edit] Iodine
Vegans in countries where the soil is low in iodine, such as the United Kingdom, should ensure they get adequate amounts of this halogen, since dairy products and fish are the most important sources of iodine in these countries.[citation needed] When supplementing the diet with iodine-rich seaweeds such as nori and kelp, moderation is advised, though, because there is a danger of overdosing. Iodized salt may also be used.
[edit] Iron
Iron is said by the Vegan Society to be present in many typically vegan foodstuffs, including grains, nuts and green leaves. However, the iron in these sources is in a less easily absorbed form (non-heme as opposed to heme iron). Nevertheless, the Society quotes research to show that iron deficiency is no more prevalent in vegans than in the general population (possibly as a result of the higher vitamin C intake of most vegans; vitamin C has been linked to increased iron absorption when taken in conjunction with the source of iron). Vitamin C is the most potent of a list of several known iron enhancers that also includes other organic acids found in fruit and vegetables, as well as sugars. In a 1985 Indian study, iron-deficiency anemia in vegetarian children was successfully treated by adding vitamin C to meals. Some consider vegans to be at lower risk of iron deficiency anemia than ovo-lacto-vegetarians because, while eggs are listed as a "fair source" of iron, dairy products contain little and poorly absorbed iron, and both have been found to reduce iron absorption from other food sources consumed at the same time. Other (vegan) foods that may reduce iron absorption are spinach and other high-oxalic acid foods, high-phytic acid foods such as soybeans and unfermented, unsprouted whole-grain cereals, and tannin-rich beverages such as coffee and tea. On the other hand, spinach, soybeans and whole-grain cereals are rich in iron and, when combined with iron enhancers, may constitute good sources of iron. The interaction between iron enhancers and inhibitors in whole foods has not been extensively studied, though.
Vegetarians have been found to have, on the average, normal hemoglobin levels, but lower ferritin levels. On the one hand, this means that vegetarians need a more steady supply of dietary iron, on the other, high ferritin levels have been implied as a risk factor for colorectal cancer and bacterial infections.
[edit] Protein and amino acids
The American Dietetic Association states that "plant sources of protein alone can provide adequate amounts of essential amino acids if a variety of plant foods are consumed and energy needs are met."[2] Raw nuts are high in protein.
[edit] Trans-fats
It is wise for vegans and non-vegans alike to avoid trans fats (found in hydrogenated and partially hydrogenated oils), in order to have good nutrition. These transfats are most commonly found in snack food, fried food, and other highly-processed foods. Most fast-food restaurants use hydrogenated oil when cooking their french fries. Partially hydrogenated oils contain the highest proportion of trans-fatty acids. Consumer awareness has recently led to an increased supply of foods such as margarine with no hydrogenated oils.
[edit] Vitamins and minerals
There is no reliable plant source for Vitamin B12. Vitamin B12 can be obtained in some fortified yeast extracts (check labels) and other fortified products such as soy milks. No scientific test has yet found a reliable vegetable source (ie. one that works consistently for all testees) of B12, and the UK Vegan Society recommends the use of supplements derived from bacteria, and that a minimum of 3μg (micrograms) of B12 be consumed daily.
While it would take one to five years to exhaust the body's reserve of vitamin B12, serious health consequences are a very real risk.[3] In a recent laboratory study, 60% of the strict vegan participants' B12 and iron levels were compromised, as compared with the lacto- or lacto-ovo-vegetarian participants (who were able to acquire vitamin B12 from these animal sources).[4] In addition, lower counts of lymphocytes (the white blood cells responsible for immune system responses) and platelets (responsible for blood coagulation) and alterations in the iron metabolism and transport, were demonstrated.
Another B12 study was conducted in rural Africa, partially backed by the U.S. based National Cattlemen's Beef Association, which demonstrated a dramatic improvement in the health of individuals who had, prior to the study, been on diets completely lacking in animal products. The study concluded that the added nutrients, especially vitamin B12 contained in the meat and milk improved the health of the children in the study.[5] The author of the study, Professor Lindsay Allen of the United States Agricultural Research Service, declared: "There's absolutely no question that it's unethical for parents to bring up their children as strict vegans, unless those who practiced them were well-informed about how to add back the missing nutrients through supplements or fortified foods."[5][6][7] However, the British Dietetic Association contended that the findings of the study were not applicable to vegan children in the developed world. They note that B12, reliably found only in animal products, is now included in many fortified foods generally available. Noting that the impoverished children in the study had diets deficient in zinc, B12 and iron, they concluded, "There is no evidence that our vegan and vegetarian children in this country suffer impaired development". They did note, however, that young children, pregnant and nursing women are vulnerable as vegans, urging parents to review their children's diets to be sure that they have a well-balanced diet.[8]
[edit] Calcium
Calcium may also be a concern to vegans who are not eating a variety of foods, especially leafy green vegetables (such as spinach, kale, collard greens, cabbage, etc.), almonds, oats, soy products (soy milk, tofu, etc.), sesame seeds, most beans, and dried fruits, most of which should be included in any diet, vegan or not.
The USDA's study on calcium and osteoporosis in women began with the premise that animal proteins create sulphur in the body, which leeches out calcium from the bones. The results, though, were more complex: the vegan subjects lost bone density at the same rate as their vegetarian and non-vegetarian peers; when put on a weight-bearing exercise regimen, the vegan subjects built bone density at a significantly higher rate than the other subjects. The researchers remark, "If you have less bone formation, the result is the same as if you had an increase in bone resorption. So, even though bone resorption was the same in both groups of volunteers, the lower amount of bone formation in the omnivore women could lead to a decrease in their bone density."
[edit] DHA
One omega-3 fatty acid is docosahexaenoic acid (DHA). Vegan DHA sources include NuTru(TM) and DEVA, derived from blue-green algae. DHA is produced by the body from ALA in non-diabetics, thus it is classified as a non-essential fatty acid, whereas ALA is an essential fatty acid (can only be obtained through eating). This fatty acid is important for brain function, eye function, and for the cellular transport of nutrients. Alpha-linoleic Acid, ALA is converted by the body into DHA and EPA. Soybeans, walnuts, flaxseed, pumpkin seeds, and canola oil all contain high amounts of ALA. In theory, one tablespoon of flaxseeds should provide the daily recommendation of ALA - from which the body would produce needed DHA and EPA. However, a healthy person's body converts only 20% of the ALA. Additionally, studies have shown that production of DHA and EPA from ALA may be insufficient, especially for anyone who is elderly, unfit, ill or pregnant. To obtain the same benefit, it has been estimated that 10x the amount of ALA as DHA must be consumed. [4] For non-vegans, good sources for this omega-3 fatty acid include edible marine fish and shellfish and eggs.
[edit] Iodine
Residents of the UK may find themselves iodine-deficient if they rely on local produce, since in the UK iodine is usually obtained via dairy products rather than iodized salt that is more common elsewhere. The Vegan Society says, "Iodine is typically undesirably low (about 50 micrograms/day compared to a recommended level of about 150 micrograms per day) in UK vegan diets unless supplements, iodine rich seaweeds or foods containing such seaweeds are consumed. The low iodine levels in many plant foods reflects the low iodine levels in the UK soil, due in part to the recent ice-age." This demonstrates that location may also be a factor in what deficiencies may be present in any given diet.
[edit] Iron
Iron is present in many typically vegan foodstuffs. These include grains, nuts and green leaves, although the iron in these sources is in a less easily absorbed, non-heme form. Nevertheless, the Vegan Society quotes research to show that iron deficiency is no more prevalent in vegans than in the general population. This research did not account for the fact that many vegans take nutritional supplements that are not found in food alone, whereas other research that excludes this subset of people does indeed show a marked iron deficiency among a majority of those studied.
Vitamin C facilitates the absorption of iron, and, indeed, can double or triple the amount of iron absorbed when taken with food. Vegans typically have high levels of vitamin C in their diets, which may account for the rarity of anaemia amongst them. However, diets lacking in heme-form iron can contribute to anemia and impair performance in endurance athletes (especially females, see menstrual cycle) due to their increased need for hemoglobin in the blood.
[edit] Protein
Frances Moore Lappé's 1971 bestseller Diet for a Small Planet popularized the claim that the protein in plant foods was incomplete and that vegetarians had to "combine" different plant foods (e.g., beans and grains) in order to get a "complete" protein. A decade later in The McDougall Plan (1983) Dr. John McDougall responded that this idea is incorrect and that common plant foods actually contain complete proteins. In The McDougall Program (1990) he wrote, "Nature designed and synthesized our foods complete with all the essential nutrients for human life long before they reach the dinner table. All the essential and nonessential amino acids are represented in single unrefined starches such as rice, corn, wheat, and potatoes in amounts in excess of every individual's needs, even if they are endurance athletes or weight lifters." The World Health Organization standard for protein intake is cited in support of this interpretation. Lappé herself renounced the idea that protein combining was necessary in the 10th edition of Diet for a Small Planet, stating:
With three important exceptions, there is little danger of protein deficiency in a plant food diet. The exceptions are diets very heavily dependent on [1] fruit or on [2] some tubers, such as sweet potatoes or cassava, or on [3] junk food (refined flours, sugars, and fat). Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories. In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein."
[edit] Vitamin B12
Vitamin B12, a bacterial product, cannot be reliably found in plant foods, and so vegans are recommended to eat foods with B12 added (such as fortified soy milk, fortified margarines, or many fortified commercial breakfast cereals), certain brands of fortified nutritional yeast[5], or take dietary supplements (a good multivitamin will likely include B12 in sufficient quantities). Some tempeh and some other fermented foods may contain B12 due to bacterial contamination, but cannot be considered reliable sources [6]. Some non-animal organisms (notably seaweeds) and fungi (mushrooms) absorb trace amounts of B12 from growing in bacteria-rich environments. Raw and dried nori, both sometimes touted as vegan B12 sources, have failed tests for B12 activity.[7]
Inadequate absorption of the body's stores of vitamin B12 poses a health risk, so the vitamin must often be ingested through fortified products and suppliments. Older people—vegan and non-vegan alike—may experience difficulties in absorbing B12 from their food, and anemia (caused by B12 deficiency) is not unknown amongst omnivores. B12 deficiency has symptoms such as loss of appetite, fatigue, weakness, dizziness and confusion and can lead to irreversible neurological damage. It is particularly problematic for pregnant women and fetal development, as well as for infants who are breast-fed by a deficient mother.
The Vegan Society concludes: "...the human need for B12 has increased over time. The longer a vegan does not supplement with B12, the lower their active B12 levels will drop..." [8]
[edit] Vitamin D
Vitamin D (vitamin D2) occurs naturally in some mushrooms (eg. shiitake) and fungi. It is also available in fortified foods and can be produced in the body from sunlight shining on the skin.
Vitamin D3 only occurs naturally in animal-derived foods, however, like other D-vitamins, it is naturally produced in the skin in response to sunlight, so it is not necessary to ingest it.
[edit] References
- ^ Kris-Etherton P, Eckel RH, Howard BV, St Jeor S, Bazzarre TL (2001). "AHA Science Advisory: Lyon Diet Heart Study. Benefits of a Mediterranean-style, National Cholesterol Education Program/American Heart Association Step I Dietary Pattern on Cardiovascular Disease". Circulation 103 (13): 1823-5. PMID 11282918.
- ^ Messina VK, Burke KI (1997). "Position of the American Dietetic Association: vegetarian diets". J Am Diet Assoc 97 (11): 1317-21. PMID 9366873.
- ^ Vitamin B12 (cobalamin). Merck Manual Home Edition. Retrieved on 2006-10-30.
- ^ Obeid R, Geisel J, Schorr H, Hubner U, Herrmann W. (2002). "The impact of vegetarianism on some haematological parameters". Eur J Haematol. 69 (5-6): 275-9. PMID 12460231.
- ^ a b Michelle Roberts. "Children 'harmed' by vegan diets", BBC, 21 February 2005.
- ^ Danielsen, Christian. "UCD professor's comments on vegan diet hotly debated", California Aggie, 2005-03-02. Retrieved on 2006-10-30.
- ^ Former Beatle Paul McCartney Calls GL-CRSP Nutrition Study 'Rubbish' (PDF). Ruminations Newsletter (Spring 2005). Retrieved on 2006-10-31.
- ^ Left, Sarah (2005-02-21). Raising children as vegans 'unethical', says professor. Guardian Unlimited. Guardian Newspapers Limited. Retrieved on 2006-10-31.
- Walsh, Stephen. Plant Based Nutrition and Health, The Vegan Society 2003, ISBN 0-907337-26-0 (paperback), ISBN 0-907337-27-9 (hardback).
- Langley, Gill. Vegan Nutrition: a survey of research, The Vegan Society 1988, ISBN 0-907337-15-5
- Greger, Michael. “Optimum Vegetarian Nutrition”, on CD-ROM. May be found online at http://veganmd.com/.
- Seshadri S., Shah A., Bhade S. Haematologic response of anaemic preschool children to ascorbic acid supplementation, Human Nutrition, April 1985
