By vegetarian, I mean someone who does not eat the flesh of animals. This includes fish and chicken. By vegan, I mean someone who does not eat any animal produce, including milk or eggs.
Dr. Michael Greger M.D. ("The Vegan M.D.") has an informative and witty lecture "Optimum Vegetarian Nutrition: Omega 3 and B12".
In a nutshell, vegetarians & vegans don't live any longer than omnivores – as shown in a study of 28,000 subjects. Vegetarians & vegans have the same rates of coronary heart disease as omnivores, but double the rates of degenerative brain diseases like Alzheimer's Disease. WHY? There are two reasons.
1) Vegetarians and vegans don't eat oily fish and most don't eat cracked or ground-up flaxseed/linseed either. This means a deficiency in omega-3 fats. This increases the risk of diabetes, certain cancers and coronary heart disease.
Men are much poorer converters of alpha-linolenic acid (the omega-3 fatty acid in flaxseeds/linseeds) into DHA than
See Eicosapentaenoic and docosapentaenoic acids are the principal products of α-linolenic acid metabolism in young men,
Conversion of α-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women and
Limited Synthesis of Long Chain Polyunsaturates in Adults: Implications
for Their Dietary Essentiality and Use as Supplements.
2) Only animal produce naturally contains Vitamin B12. Lack of B12 in the diet raises the level of homocysteine in the blood, which damages artery walls. This raises the risk of coronary heart disease & doubles the risk of degenerative brain diseases like Alzheimer's Disease.
3) Diets low in Vitamin K2 increase the risk factor for CHD, osteoporosis and weak teeth. See Vitamin K.
What to do?
1) Eat ~25g/day of ground flaxseeds (or supplement with ~10g/day of flaxseed oil). Vegan men should also supplement with ~1000mg/day vegan DHA.
2) Eat foods fortified with vegan B12 or supplement with vegan B12.
3) Eat foods high in Vitamin K2. See
For Vegans for a list of things to maximise health on a vegan diet.