It is true that B12 is available only from animal products, but only a very small amount of animal products need to be consumed to satisfy the body's need. I believe it takes three months for the body's reserves of B12 to be depleted. Meat and animal products need be no more thn 2 - 5% of your diet (like the diet of natural primates) as long as the rest is healthy vegan food. Think of apes, the strongest primate in the world-- their diet is 98% vegan.
I would not trust a study of veganism in India where malnutrition is rampant and choices for food are limited due to poverty and prob also a lack of education about nutrition.
The Mayo clinic and a recent book called the China Study have found that the single greatest predictor of cancer development are the amount of animal products in a person's diet. The higher the amount of vegan food in the person's diet, the lower their chance of developing cancer. The correlation is stronger even than exposure to pesticides.
(And the only proven method to expand lifespan, btw, is a restricted calorie diet, more or less regardless of what you're eating.)
I have been 90-100% vegan on any given day since early 2004; I eat meat about 1-2x a month and small amounts of dairy about 2-3x a week. The rest is strictly vegan... the difference in my health between then and now is remarkable, I basically don't get sick anymore, even when there is a nasty flu bug or cold going through my family. I used to always be the sickest one in the family when we got sick.
However I think the nutritional needs of children are very different from adults, they should probably have a much higher intake of animal products (babies are designed to live only a dairy, mother's milk, for the first years of life, after all, which is how it was done until baby formula was developed). But as adults I believe those animal products are harmful in anything other than very small quantities and study after study proves the benefits of vegan foods.
I'm sorry if I sound like a foody or food snob but I discovered veganism when I was gravely ill for more than a year with a bacterial infection that was antibiotic resistant. I was desperate to get better and researched everything I could about nutrition. It was only when I went nearly completely vegan, taking in only small amounts of animal products, that I got better. I would love for other people to realize the health benefits of vegan foods and the damage of a high intake of meat and dairy products.
Also, for those who eat beef, there have been studies indicating that many cases of Alzheimers are actually misdiagnosed cases of mad cow-- the diagnosis cannot be definitive unless an autopsy is done on the brain. Many post-mortem examinations of "Alzheimer's" brains actually indicate mad cow.
Even if you can only get your diet to 80% vegan (80% strictly plant produce-- grains, legumes, nuts, vegetables, fruits, plant oils, etc) you would see a vast benefit to yourself.
There's no doubt that you don't need a lot to survive. Hell, I'm a weight lifter and even I only eat a small amount of lean meat once a day for the protein value. My only point was that it is, indeed, needed and a naturally occuring aspect of human nature. One thing that really gets me is the people that say, "People aren't meant to eat animals! It's not nature! It won't hurt you to be vegan!"... when in fact... it does hurt you to be 100% vegan. But yeah, too much animal consumption leads to increases in LDL cholesterol (which in turn raises blood pressure), increases fatty lipids (and, therefore, waiseline), increases odds of heart disease, etc.
