In fact, when I had a looser schedule, I would have a cup of coffee and go riding (or go to the gym) because I had enough glycogen, and enough food inside me digesting, to keep me going for a few hours. That really helped with weight loss, because if I did run out of glucose, my body had to burn fat ... which was the point of it all. Of course, I always had a Powerbar stashed just in case.