Why weren't our ancestors Diabetic?

Our ancestors have been eating rice, wheat, etc. for ages. Why weren't they diabetic and in the present situation almost 1 in 3 is diabetic. The answer to the question is, our ancestors were consuming food required for the body and everything was naturally. Nowadays we consume refined and processed foods, again in abundance which ultimately leads to the fat deposits in our body. Another reason is eating balanced food with lot of fibre (vegetables and fruits). In the present situation, we fail to consume fibre rich foods.