Theres a lot of different reasons that could be the case. Diet is an extremely personal thing and people making generalizations because of intestinal length and the shape of teeth miss the point. that's one reason why I disagree with Ava's position here. It's just a theory that all *metabolically healthy* people can thrive on a vegetarian diet. And a huge majority of people in the modern world are NOT metabolically healthy. Which doesnt necessarily mean they thrive on an animal based diet but it is often the case that people with poor nutrient uptake do better with animal fats and animal proteins. like I said, its mostly case by case and it's extremely hard to generalize diet. (full disclosure damaged myself with drugs and alcohol when young, lived on a vegan or vegetarian diet for 20 years but didn't begin to heal until I added animal products back into my diet YMMV)