Evolution doesn't really explain anything, and it has no goals. And the obesity epidemic is due to the fact that for hundreds of millions of years all living creatures have tried to survive in conditions of a lack of food resources. And if we managed to get to food, then we have a lot of genes in order to keep this food in reserve, for "obligatory" hunger in the future. And only in recent decades, a significant part of the population suddenly found itself in conditions of an excess of high-calorie food. Now the selection process should begin under new conditions, and in a couple of million years evolution would "lead" us to the norm. However, I think a person will solve this problem one way or another much faster :)
Evolution presupposes random mutations, as a result of which the individual who is most adapted to the changed conditions survives and continues.
According to the laws of nature, a "man with a belly" is most at risk of not extending the genus and his set of genes because a) there is a high likelihood of developing cardiovascular and not only diseases; b) low probability of procreation.
Therefore, the industrial revolution, which resulted in a large number of people with "belly" - is a kind of next stage of evolution, as a result which someone will retire.