Why should our bodies evolve to become less efficient and thus to lower our survival capabilities? I think the evolution at play here is not there. It's in sel

Why should our bodies evolve to become less efficient and thus to lower our survival capabilities? I think the evolution at play here is not there. It's in self-control and being to maintain a healthy diet in the face of abundance. Indeed, those who can't do that and, for instance, become obese lower their survival rates because of the negative consequences. However this does not seem to affect reproduction rates (or does it?), which is key for evolution.