Vegetarian, vegan and raw diets can be healthful […] but to call these diets “natural” for humans is a bit of a stretch in terms of evolution, according to two recent studies.

Eating meat and cooking food made us human, the studies suggest, enabling the brains of our prehuman ancestors to grow dramatically over a few million years.
the new studies demonstrate that it would have been biologically implausible for humans to evolve such a large brain on a raw, vegan diet and that meat-eating was a crucial element of human evolution at least a million years before the dawn of humankind.
At the core of this research is the understanding that the modern human brain consumes 20 percent of the body’s energy at rest, twice that of other primates. Meat and cooked foods were needed to provide the necessary calorie boost to feed a growing brain.
early humans eating only raw vegetation would have needed to munch for more than nine hours a day to consume enough calories, the researchers calculated. Thus, a raw, vegan diet would have been unlikely, given the danger and other difficulties of gathering so much food.

Cooking makes more foods edible year-round and releases more nutrients and calories from both vegetables and meat, Herculano-Houzel said.
[Sorry, vegans: Eating meat and cooking food is how humans got their big brains sur]