Too many people who exercise purposefully do not eat before they exercise. They think they should exercise on empty, to prevent intestinal distress. While this may be OK for a short bout of exercise, when they build up to an hour of more of exercise, they start to run out of energy. Thye experience needless fatigue.
Research indicates consuming 100 to 300 calories (depending on your body size and how hard you will be exercising) within the hour before you exercise can improve performance -- to say nothing of enjoyment of the the session. Hence, if you have been avoiding food out of fear of "rapid transit", you should start to train your intestinal track to lean how to digest food while you exercise. This is important if you plan to workout for more than an hour. Start with a saltine, apretsel, a bite of banana, and work up to two saltines, two pretzels, two bites of banana ... With time, your intestinal track will adjust to digesting food while you exercise, and you'll have better, stronger, more enjoyable workouts.
Training your intestinal track as well as your heart, lungs and muscles is important if you plan to do workouts that last longer than one hour!
Nancy Clark MS RD CSSD