Our earliest ancestors knew it much better than any of us. For them most of such foods (like sugar) wasn't readily available but whenever and in whatever form they got it, they used to consume it much more. They reasoned that Sugar saved them from many diseases. In fact I l've had my all ancestors eat a lot of honey, jaggery made of sugarcane and never had any issues because of them. It's possible that the Sugar (with residual sulphur) we consume now is a big cause for diabetes.