Still.. if you asked me why marathon runners had bowel cancer I would say that they eat more low fiber carbs than is possible for a normal person..

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.

I find this a curious hypothesis, to say the least.

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.