Vegetarian nutrition

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Vegetarian nutrition is the set of health-related challenges and advantages of vegetarian diets.

Evidence suggests that vegetarians are generally healthier and live longer than non-vegetarians. They have lower rates of coronary heart disease, obesity, hypertension, type 2 diabetes and some forms of cancer. Vegetarian diets tend to be rich in carbohydrates, omega-6 fatty acids, dietary fibre, carotenoids, folic acid, vitamin C, vitamin E, potassium and magnesium and low in saturated fat, cholesterol, and animal protein.

However, vegetarian diets can also be relatively low in protein, iron, zinc, vitamin B12, calcium and other nutrients. Nonetheless, well-planned vegetarian and 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.

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[edit] Benefits of a vegetarian diet

Vegetarian diets are usually rich in carbohydrates, omega-6 fatty acids, dietary fibre, carotenoids, folic acid, vitamin C, vitamin E, potassium and magnesium.[1][2] They contain lower levels of saturated fat, cholesterol, and animal protein.[1]

Evidence suggests that the health of vegetarians compares favourably with that of non-vegetarians.[3] British vegetarians have lower death rates than non-vegetarians,[3][4] although this may be due to non-dietary lifestyle factors, such as a low prevalence of smoking and the generally high socio-economic status of vegetarians, or to aspects of the diet other than the avoidance of meat and fish.[5]

One review found that mortality from coronary heart disease was 24% lower in vegetarians than in nonvegetarians.[6] Studies of cancer have not shown clear differences in cancer rates between vegetarians and non-vegetarians.[2] There is evidence that vegetarians tend to have a lower body mass index,[1][2] lower risk of obesity,[7] lower blood cholesterol levels,[1][2] lower homocysteine levels,[2], lower risk of high blood pressure,[1][7] and lower risk of type 2 diabetes.[1][7] One large prospective study found that non-meat-eaters had only half the risk of meat eaters of requiring an emergency appendectomy.[3]

[edit] Potential nutrient deficiencies

Vegetarian diets are often relatively low in protein, calcium, saturated fat, omega-3 fatty acids, retinol, vitamin D, riboflavin, vitamin B12, vitamin A, iodine and zinc.[1][2] Vegans may have particularly low intakes of vitamin B12 and calcium.[2] Nonetheless, well-planned vegetarian and 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.[1]

[edit] Protein

The typical vegetarian gets adequate protein as long as caloric intake is adequate and a variety of foods are eaten.[8] A typical vegetarian gets less protein than the typical non-vegetarian which may be beneficial.[9][10] USDA's tables provide information about the protein content of most foods, and the Institute of Medicine's DRI tables show the amount of recommended protein intake.

Due to the lower digestibility of plant proteins, however, the ADA states "protein needs might be higher than the RDA in vegetarians whose dietary protein sources are mainly those that are less well digested, such as some cereals and legumes."[1]

[edit] Combining Proteins

A widely held myth is the idea of protein combining: that vegetarians must eat grains and beans within a few hours of each other in order to make a 'complete' protein which contains all 8 "essential amino acids". While this myth is widely believed, it has never been substantiated by research.

The protein-combining theory was brought to popular attention in Frances Moore Lappe's 1971 bestseller Diet for a Small Planet. In later editions of the book, as early as 1981, Lappe withdrew her contention that protein 'combining' is necessary. John McDougall concurs with Lappe's 1981 conclusion, providing a table comparing amino acid requirements with the amino acids in common plant foods. McDougall says "many people believe that animal foods contain protein that is superior in quality to the protein found in plants. This is a misconception dating back to 1914, when Osborn and Mendel studied the protein requirements of laboratory rats. (11) ... It has since been shown that the initial premise that animal products supplied the most ideal protein pattern for humans, as it did for rats, was incorrect."McDougall still challenges those who perpetuate the protein-combining myth by demanding that they produce evidence to support their claims.[11]

[edit] Iron

A study in the Journal of the American Dietetic Association found that while iron deficiency anemia is not more common among vegetarians, "Vegetarian children had ... reduced levels of haemoglobin and iron compared to omnivores" due "to the absence of animal iron sources with high utilizability".[12]

Meat, fish and poultry are the only sources of heme iron; plants contain non-heme iron. The human body absorbs non-heme iron less efficiently.[12]

[edit] Zinc

Western vegetarians and vegans have not been found to suffer from overt zinc deficiencies any more than meat-eaters.[13] However, phytates in many whole-grains and fiber in many foods may interfere with zinc absorption and marginal zinc intake has poorly understood effects.[1]

[edit] Vitamin B12

One of the concerns of a vegetarian diet is that plant foods do not contain vitamin B12 except when they are contaminated by microorganisms or have vitamin B12 added to them.[14] Lack of Vitamin B12 causes anemia and this vitamin is produced only by bacteria which are found only in animals.[15]

The only reliable unfortified sources of vitamin B12 are meat, dairy products and eggs.[16] According to the USDA, strict vegetarians and people above 50 are at the highest risk of not getting enough vitamin B12.[15]

Animals, including humans, must ingest B12 to maintain proper B12 levels.[17] Numerous studies demonstrate that vegetarians who are not taking B12 supplements can improve their health by improving their B12 status.[18]

[edit] Omega-3 fatty acids

Vegetarian sources of Omega-3 fatty acids include flaxseeds and flaxseed oil, olive oil, walnuts, canola (rapeseed) oil, avocado, and eggs.

Vegetarian sources of omega-3 fatty acids are primarily the short chain variety and likely to have lower concentrations of the particular essential fatty acids (EFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The body can synthesize small quantities of EPA and DHA from other omega-3 fatty acids, such as alpha-linolenic acids, which are present in vegetarian sources of omega-3 fatty acids. The human body can also convert DHA into EPA. DHA supplements derived from DHA-rich microalgae are available. Whilst the human body can in theory do this conversion, in practice modern diets and lifestyles reduce the effectiveness of the conversion systems. Roughly ten times more of the short chain omega-3s must be consumed to have the same effect as the long chain form from fish oil.[19]

While there is no scientific consensus on the role of omega-3 fatty acids, it is generally believed that they may reduce the risk of coronary heart disease, lower triglycerides, stabilize mood and help prevent depression, help prevent ADD, reduce joint pain and other rheumatoid problems and reduce the risk of dementia in older age. It must also be noted that, while Omega 3 from fish oil is beneficial, there is debate about the benefits of Omega 3 fats derived from plants.[20] Nutritionists advise consumers that its is safer to consume fatty fish to obtain Omega 3 rather than plant based varieties.[21]

[edit] Vitamin D

The human body can synthesize Vitamin D when skin is exposed to ultraviolet radiation from the sun. Vegans who do not eat foods or pills fortified with synthetic vitamin D and with little exposure to the sun's ultraviolet radiation, e.g. who don't expose their extremities for at least 15-30 minutes per day or those living at latitudes close to the poles, are vulnerable to Vitamin D deficiencies.

Vitamin D acts as a hormone, sending a message to the intestines to increase the absorption of calcium and phosphorus, which produces strong bones. Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization. Research also suggests that vitamin D may help maintain a healthy immune system and help regulate cell growth and differentiation.

[edit] Iodine

According the British Journal of Nutrition there is 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."[22] Iodine, however, is usually supplied by iodized salt and other sources in first world countries.

[edit] References

  1. ^ a b c d e f g h i j “Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets”. Journal of the American Dietetic Association, 2003, 06. Accessed 4 January 2007.
  2. ^ a b c d e f g Key TJ, Appleby PN, Rosell MS: “Health effects of vegetarian and vegan diets”. Proceedings of the Nutrition Society, 2006, 65:35-41. Accessed 4 January 2007.
  3. ^ a b c Appleby PN, Thorogood M, Mann JI, Key TJ: “The Oxford Vegetarian Study: an overview”. American Journal of Clinical Nutrition, 1999, 70:525S-531S. Accessed 4 January 2007.
  4. ^ Key TJ, Appleby PN, Davey GK, Allen NE, Spencer EA, Travis RC: “Mortality in British vegetarians: review and preliminary results from EPIC-Oxford”. American Journal of Clinical Nutrition, 2003, 78:533S-538S. Accessed 4 January 2007.
  5. ^ Appleby PN, Key TJ, Thorogood M, Burr ML, Mann J: “Mortality in British vegetarians”. Public Health Nutrition, 2002, 5:29-36. Accessed 4 January 2007.
  6. ^ Key TJ, Fraser GE, Thorogood M, Appleby PN, Beral V, Reeves G, Burr ML, Chang-Claude J, Frentzel-Beyme R, Kuzma JW, Mann J, McPherson K: “Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies”. American Journal of Clinical Nutrition, 1999, 70:516S-524S. Accessed 4 January 2007.
  7. ^ a b c American Heart Association: Vegetarian Diets. Accessed 4 January 2007.
  8. ^ "But how do you get enough protein?", by vegetarian society of Colorado link
  9. ^ Food Navigator USA: Low-protein diets could protect against cancer, says new study. 7 December 2006. Accessed 4 January 2007.
  10. ^ Diabetic nephropathy
  11. ^ John McDougall: “The American Heart Association Continues to Harm the Public”. The McDougall Newsletter, November 2002.
  12. ^ a b Krajcovicova-Kudlackova M, Simoncic R, Bederova A, Grancicova E, Magalova T: “Influence of vegetarian and mixed nutrition on selected haematological and biochemical parameters in children.” Nahrung, October 1997, 41:311-314.
  13. ^ Freeland-Graves J. H., Bodzy P. W., Epright M. A.: “Zinc status of vegetarians”. Journal of the American Dietetic Association, 1980, 77:655-661
  14. ^ Reed Mangels: Vitamin B12 in the Vegan Diet. The Vegetarian Resource Group. Accessed 4 January 2007.
  15. ^ a b Gerald Combs, Jr.: B12 – More Important Than You Think. United States Depertment of Agriculture: Agricultural Research Service. Accessed 4 January 2007.
  16. ^ The Vegetarian Society: Vitamin B12. Accessed 4 January 2007.
  17. ^ Callender S. T., Spray G. H.: “Latent pernicious anemia”. Br. J. Haematol., 1962, 8:230-240
  18. ^ veganhealth.org: B12 Status: Immerman - The Exception. Accessed 4 January 2007.
  19. ^ [1]
  20. ^ Omega 3 in the 'OJ'? ABC News
  21. ^ Do Omega 3 Products Live up to Claims? By Darla Sitton and Gailon Totheroh CBN News, January 17, 2007
  22. ^ Thomas Remer, Annette Neubert and Friedrich Manz: “Increased risk of iodine deficiency with vegetarian nutrition”. British Journal of Nutrition, 1999, 81:45-49. Accessed 4 January 2007.

[edit] See also

[edit] Further reading

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