The workout: A sweat-inducing evening spin class.
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.