All of the diseases we define as normal, didn’t seem to affect our paleolithic ancestors or contemporary hunter gatherers. Why is that??
Well for a long time, humans ate primarily meat and fish, along with fruits and vegetables, nuts and seeds and some starchy plants like sweet potatoes. We’ve also shifted our lifestyles to more of a sedentary way of living away from a very active lifestyle. Finally, we began eating a much less variety of foods, because we decreased our diet to three or four staple crops.
All of these factors have played a role in the uptick of overweight and obese kids and adults living in the US and modern world.