Meat was the main course of our ancestral hunter-gatherer diet.
Things changed 10,000 years ago with the agricultural revolution. We see it in the fossil teeth. Cavities and tooth enamel defects, like enamel hypoplasia, start to pop up with increasing frequency.
For example, 6,000 years ago in Upper Egypt, the Badarian culture started planting wheat, barley, lentils, and tubers.
Malnourishment ensued.