July 2, 2008
http://www.thirdage.com/
The vegan diet can also be called "strict" vegetarianism, in that it excludes not only meat and fish but also eggs, honey and milk products. Many practitioners of the vegan diet additionally avoid the use of animal products in other forms, such as clothing (wool, leather, silk), jewelry (pearls) and cosmetics (lanolin). People who adopt veganism may do so for health reasons, ethical considerations or both. There are several forms of veganism, and these may disagree on various major and minor points. For example, the raw-food diet and the macrobiotics diet are both vegan, but while macrobiotic practitioners believe that raw food is unhealthy raw-foodists believe that cooked food is the source of many health problems.
The word "vegan" was created in 1944 by Elsie Shrigley and Donald Watson, "pure vegetarians" annoyed by the fact that many people who called themselves vegetarian ate dairy products and even fish. They combined first three and last two letters of vegetarian to form "vegan", thereby intending to indicate that veganism was "the beginning and end of vegetarian."
Some proponents of veganism claim that a vegan diet can cure many health conditions. However, in attempting to actually scientifically verify such claims one runs into a significant problem: it is difficult, if not impossible, to design a scientifically reliable study of diet.
For the results of a study to be trustworthy, participants and researchers must be kept in the dark ("blind") regarding who received the treatment under study (the "active group") and who received a placebo treatment (the "control group"). If practitioners and/or researchers know who is in which group, numerous confounding factors will take over and produce misleading results. These factors include observer bias, reporting bias and the placebo effect. The many ways in which these confounders skew the results of unblinded studies are discussed in detail in Why Does This Database Rely on Double-blind Studies? To briefly summarize this complex issue: unblinded studies usually mean little to nothing. Unfortunately, it's difficult to keep study participants in the dark regarding whether the are on a vegan diet!
Rheumatoid arthritis is the prime condition for which veganism has been advocated. In several studies, people put on a vegan diet showed improvement in symptoms as compared to those who were allowed to eat in an ordinary fashion. 1-3 However, as noted above, the absence of blinding makes these results unreliable. These studies would have been more meaningful if, for example, all participants ate a vegan diet and in addition consumed cookies that, unbeknownst to them contain either animal fats or vegetable fats. Unfortunately, no studies using this or any other properly blinded control treatment have been reported.
A small study of similarly inadequate design weakly hints that vegan diet might be helpful for fibromyalgia . 4 Another small study compared vegan diet to an antidepressant for treatment for fibromyalgia, and the antidepressant appeared to be more effective. 5 (Here, however, unconscious bias may have been working in the opposite direction: this study was conducted in Bangladesh, where vegan diet is not exceptional, while western drugs could very well have something of a "magical" aura!)
Even weaker evidence hints that vegan diets might be helpful for treating hypertension , 6 as well as preventing heart disease and cancer .
Safety Issues
With the exception of vitamin B 12 a vegan diet can in principle provide all necessary nutrients. However, in practice, vegans are frequently deficient in calcium , iron , vitamin D , selenium , phosphorous , and zinc . 10
Vitamin B 12 presents a special issue. This vitamin is not provided to any meaningful extent by non-plant foods. (The algae spirulina contains B 12 , but in a non-absorbable form.) Deficiency in B 12 is therefore inevitable among those who follow a strict vegan diet and do not take supplements. 7-11 Such deficiency has led to serious health consequences among vegans as well as breast-fed infants of vegan mothers. 12-13 When severe, B 12 deficiency can cause irreversible nerve damage. Mild deficiency leads to anemia and, in association with other common deficiencies, increased risk of bone thinning and fracture..
There is an additional potential issue for athletes to consider: A vegan diet is very low in the non-essential nutrient creatine . It is possible that creatine supplements may be particularly helpful for vegan athletes. 14-15
References
1. Kjeldsen-Kragh J. Rheumatoid arthritis treated with vegetarian diets. Am J Clin Nutr . 1999;70:594S-600S.
2. Kjeldsen-Kragh J, Haugen M, Borchgrevink CF, et al. Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis. Lancet . 1991;338:899–902
3. Nenonen M, Helve T, Hanninen O. Effects of uncooked vegan food "living food" on rheumatoid arthritis, a three-month controlled and randomised study [abstract]. Am J Clin Nutr . 1992;56:762.
4. Kaartinen K, Lammi K, Hypen M et al. Vegan diet alleviates fibromyalgia symptoms. Scand J Rheumatol . 2000;29:308-13.
5. Azad KA, Alam MN, Haq SA et al. Vegetarian diet in the treatment of fibromyalgia. Bangladesh Med Res Counc Bull. 2001;26:41-7.
6. Berkow SE, Barnard ND. Blood pressure regulation and vegetarian diets. Nutr Rev . 2005;63:1-8.
7. Obeid R, Geisel J, Schorr H et al. The impact of vegetarianism on some haematological parameters. Eur J Haematol. 2002;69:275-9.
8. Kwok T, Cheng G, Woo J et al. Independent effect of vitamin B12 deficiency on hematological status in older Chinese vegetarian women. Am J Hematol. 2002;70:186-90.
9. Herrmann W, Knapp JP. Hyperhomocysteinemia: a new risk factor for degenerative diseases. Clin Lab . 2002;48:471-81.
10. Turner-McGrievy GM, Barnard ND, Scialli AR et al. Effects of a low-fat vegan diet and a Step II diet on macro- and micronutrient intakes in overweight postmenopausal women. Nutrition. 2004;20:738-46.
11. Donaldson MS. Metabolic vitamin B12 status on a mostly raw vegan diet with follow-up using tablets, nutritional yeast, or probiotic supplements. Ann Nutr Metab . 2001;44:229-34.
12. Weiss R, Fogelman Y, Bennett M. Severe vitamin B12 deficiency in an infant associated with a maternal deficiency and a strict vegetarian diet. J Pediatr Hematol Oncol . 2004;26:270-1.
13. Chiron R, Dabadie A, Gandemer-Delignieres V et al. Anemia and limping in a vegetarian adolescent] Arch Pediatr . 2001;8:62-5.
14. Venderley AM, Campbell WW. Vegetarian diets : nutritional considerations for athletes. Sports Med . 2006;36:293-305.
15. Burke DG, Chilibeck PD, Parise G et al. Effect of creatine and weight training on muscle creatine and performance in vegetarians. Med Sci Sports Exerc . 2003;35:1946-55.
16. Davis BC, Kris-Etherton PM. Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications. Am J Clin Nutr. 2003;78:640S-646S.
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