There's a lot of body stress on repairing, maintaining and improving endurance
Maybe that skyrockets cellular division which would maybe would explain some of the impact?
The theory that exercise is harmful seems more like a fanciful wish than a probability given other correlation in environment and behavior where much of our environment is poorly tested and probably harmful.
So I'm a marathon runner (ran a 3:08 marathon this morning, actually, at age 55). The carbs I eat are neither excessive, nor low fibre.
And all the endurance athletes I know are extremely aware of their diets and the importance of eating the right mix of high quality foods.