Just to enter on the nutrition debate, in modern high-level sport the diet is considered as one of the most important parts of training. The body simply can't recover, let alone improve, if it doesn't receive replenishment after a training. Body building is different, but even for more athletic sports a balanced diet is absolutely necessary for the body to develop effectively without necessarily putting on weight through muscle mass. Another crucial part is getting a good amount of rest at night during which the body is repaired.

As for this supposed negative evolution of the human race, Philipvs Vallindervs Calicvla made a good point about our physique when compared to that of people hundreds of years ago, and I'd like to add that the fact that people generally don't need/want to perform hard labout in the Western world doesn't mean they can't; I know a whole bunch of people whose level of fitness before they started rowing was pretty average, in one case at least appalling, but plenty of exercise has increased that tremendously. I don't see any indication for some kind of negative human evolution, perhaps at worst personal neglect.