Chimps, our closest genetic relatives, eat a diet that is a vast majority of plant matter (fruits and such). They supplement their mostly vegetarian diet by hunting and eating small animals.
If you’re looking at what our ancestors’ diets were like, it depends on how far back you want to go. Originally, our oldest ancestors were tree-dwelling vegetarians, but as the lush forests of Africa dried up and died back, it forced a move to the ground. This began the shift in diet, brain size, locomotion, and everything else that makes us uniquely human.
We have canine teeth that are meant for ripping meat, incisors for cutting and chopping, and molars for grinding. Based on our dental configuration, it’s easy to see we are meant to be omnivores. In addition to this, our brain size and function takes up a significant portion of the body’s energy and there is definitely a correlation over our evolutionary path that increased meat eating has directly influenced increased brain size.