Research shows that if you're working at high intensity on an empty stomach, some of the fuel may come from your muscles. You also want to give yourself enough time to digest the food so you don't develop cramps. Use the hunger scale to help you decide what to eat. If you had an early or light lunch and rank your hunger at a one to a four, you're ready for a snack. If you're still at a five to a seven, you can probably hold off until dinner.
The snack: Half a sports bar (skip the high-fiber kind, which may cause a detour to the bathroom), one banana, one cup of applesauce or a few chocolate-covered pretzels (the small amount of caffeine and sugar provides a pick-me-up).
When: Eating 15 to 30 minutes before class will give your body enough time to digest so you won't feel uncomfortable.