Many people in the world today choose to become vegetarian for several reasons. For their religious view, health concern, or sometimes their care for animals. Being Vegetarian means not eating meat, poultry or fish. other vegan diets exclude dairy products and eggs. Vegetarian and vegan diets can vary widely. These are some reviews from journals about the health effects of vegan diets.
In general, vegetarian diets provide relatively large amounts of cereals, pulses, nuts, fruits and vegetables. In terms of nutrients, vegetarian diets are usually rich in n-6 fatty acids, dietary fibre, carotenoids, carbohydrates, , folic acid, vitamin C, vitamin E and Mg, and relatively low in protein, saturated fat, long-chain n-3 fatty acids, retinol, vitamin B(12) and Zn; vegans may have particularly low intakes of vitamin B(12) and low intakes of Ca.
Cross-sectional studies have shown that on average they have a relatively low BMI and a low plasma cholesterol concentration; recent studies have also shown higher plasma homocysteine concentrations than in non-vegetarians. Very high homocysteine levels in the blood can damage the lining of the arteries. In addition, high homocysteine levels may make blood clot more easily than it should. This can increase the risk of blood vessel blockages. A clot inside your blood vessel is called a thrombus which can travel in the bloodsteam and get stuck in your lungs (called a pulmonary embolism), in your brain (which can cause a stroke) or in your heart (which can cause a heart attack.)
vegetarians have shown a moderate reduction in mortality from Ischemic Heart Disease but little difference in other major causes of death or all-cause mortality in comparison with health-conscious non-vegetarians from the same population.
vegetarian diets, particularly vegan diets, are associated with lower BMD, (bone mineral density) which is one of osteoporosis cause., but the magnitude of the association is clinically insignificant.
Studies of cancer have not shown clear differences in cancer rates between vegetarians and non-vegetarians.
There are some case reports related to vegan diets in http://lib.bioinfo.pl/meid:101681