Sapiens: A Brief History of Humankind

by Yuval Noah Harari

By contrast, ancient foragers regularly ate dozens of different foodstuffs. The peasant’s ancient ancestor, the forager, may have eaten berries and mushrooms for breakfast; fruits, snails and turtle for lunch; and rabbit steak with wild onions for dinner. Tomorrow’s menu might have been completely different. This variety ensured that the ancient foragers received all the necessary nutrients.

Think of the calories and carbs that were burned up just foraging for food. There was no obesity crisis among ancient foragers.