Originally Posted by
stephtu
I think 40km is perfectly fine. The body has ~2000 calories in glycogen stored up to use, along with practically unlimited fat stores. He's not doing consecutive days without food.
Your glycogen stores won't be "topped off" if you haven't had anything to eat in the last 12-24 hours. Not that it matters since I don't believe the risk of bonking is what you need to worry about. I just know from personal experience that calorie restricting on days that I ride is a recipe for fatigue. Saying that you should just live with feeling hungry for large chunks of your waking hours strikes me as a
tad bit radical. One of the benefits of doing enough exercise is that it's
possible to eat more without gaining weight. So I just don't see the point of trying to mix a calorie restricted diet with moderate to higher levels of cardiovascular exercise. If you're going to fast though I would do it on days you don't exercise (assuming you have them.)