Roughly 10,000 years ago the last Ice Age finished. Within a couple thousands years of the ice sheet retreating, farming started up again and new foods evolved to be the mainstay they are in today's weight loss diet. This new weight loss diet, called Neolithic, had an immediate effect on individual health. Skeletons of Neolithic farmers show poor nourishment compared to the previous generations of Neanderthals. They expired younger, were of less stature, had more holes in their smaller amount of teeth and showed the first indication of fatness in need of weight loss.
The problem with the new weight loss diet of the Neolithic period was that we didn't advance to gobble those new foods. The diminutive persons’ digestive territory is exclusive among primates. We have no more than one stomach and a comparatively short large intestine. We are more well-matched to digesting and extracting nutrients from animal protein, fruit, nuts, and some vegetables.
Early civilizations also were more active. By running and lifting heavy objects every day you will build muscle and lose weight. Today we call this exercising vs just surviving in those days.