The feature film Forks Over Knives examines the profound claim that most, if not all, of the degenerative diseases that afflict us can be controlled, or even reversed, by rejecting animal-based and processed foods.
I did a search for this movie and did not see it discussed on peakoil.com. However, I did read a thread discussing veganism, which had quite a bit of bad information...
One argument that many make against veganism is that homo sapiens evolved from eating meat. Hell, we have incisors, so we were meant to eat meat. Fair enough, I agree. However, as the author of The China Study (a great book if you want to learn about food and nutrition) points out, whatever may have contributed to gene propagation, or evolution, does not necessarily mean it contributes to the healthiest lifestyle. As an example, consider two populations: one that eats meat and 100% of its infants survive and another that eats only plants, but only 40% of its infants survive (perhaps due to a lack of necessary amino acids). Now, the first population could all die at the age of 40, while the survivors of the second population could all live to 90. The first population would 'win' the evolutionary battle, but it would say nothing about their diet being healthier. It would merely say that the first population had access to food that helped them survive infancy. Since Americans and other industrial peoples now have access to both types of food, such a paradigm no longer exists.
One other point: if we are going to look at our distant ancestors to determine what's best to eat (which I think is a mistake since our food choices are completely different today), we ultimately evolved from herbivores. There is absolutely no reason why we couldn't evolve back into herbivores...