Some animals eat meat, some eat plants and some eat bugs. Humans can eat all 3 so they can survive in diverse situations. Most type 2 diabetics are overweight. Home page of site below tells about how fats from animals do not help you to lose weight like with fat from plants according to latest research.
This one minister has done a huge amount of experimentation along with research and site below tells some of the benefits people get with his diet, including a minister who was depressed and with more health problems than anyone I have ever heard of. You should find it interesting reading. I have been vegetarian for decades but my favorite food was meat. This has an effect on what people percieve as healthy.
Testing of people shows that meat eaters and vegetarians have same rate of B-12 deficiency. My mother ate lots of meat and needed B-12 shots. Most fruits and vegetables have all 8 essential amino acids meaning they are complete proteins. All the animals that we eat get all their protein from plants! See this site on Natural Healing. The minister found that even though meat gives you B-12, it causes you to have a greater need for B-12.