How does evolutionary biology theory help scientists to understand the problem with dieting?

A person trying to figure out their diet.  

The problem with dieting is that people use dieting as a way to become the body type that their society wants them to be. Scientists can use natural selection, a mechanism of evolutionary biology theory, to understand this problem. Since being the natural selection means that one is the most adapted to their environment, then that means the people who look like society's ideal body type are the natural selection out of everyone in their society. Scientists can further go into comprehending the reason through finding which case of natural selection is the most applicated to the reason why people diet, which is sexual selection. Sexual selection tells scientists that people are using dieting not only to become society's natural selection but the ideal partner for someone to get into a relationship with. Since our society has revolutionized to concerning our appearance affects the way people like us, society has made dieting as a way to look healthy and so people will appreciate us more, which is the reason dieting this way has become a problem.