A low-glycemic-index meal: If you’re the type of person who can’t work out on an empty stomach, you may want to try this to boost your fat burn: eat a meal made with “slow-release” carbohydrates (think: oatmeal, bran cereal, a whole-wheat bagel or toast) three hours before you work out. In a study published in the Journal of Nutrition, researchers assessed the rate of fat burn among eight healthy women after they ate two breakfasts: muesli with milk, peaches, yogurt and apple juice on one day; cornflakes with skim milk, white bread with margarine and jam and an energy drink on another day. Both meals contained similar amounts of calories, but the first breakfast (muesli) was a low-glycemic-index (GI) meal, meaning it produced smaller spikes in blood sugar than the second breakfast, which was a high-GI meal. Generally, foods that contain protein, fat and/or fiber—and are digested more slowly—fall lower on the GI scale than those that consist mostly of carbohydrate (e.g., white bread). On the days when the women ate the low-GI breakfast, they burned nearly twice as much fat during a 60-minute walk as they did on the days when they ate the high-GI meal. Why? The muesli (low-GI) breakfast was more slowly digested so it didn’t spike blood-glucose levels as high as the cornflake (high-GI) breakfast did. In turn, insulin levels didn’t spike as high either—which probably explains why the muesli-eating women burned more fat, says Ian MacDonald, Ph.D., director of research at the University of Nottingham Medical School. Insulin plays a role in signaling your body to store fat. So, lower levels of insulin might help you to burn fat. 
Water: Staying hydrated can help you perform better: in one study, people who were just slightly dehydrated were typically only able to run, for example, about 75 percent as hard as usual. Hydrate pre-exercise with 2 to 3 cups of water, 2 to 3 hours before exercising.

Chocolate milk: If your workout lasts an hour or more, have a glass of chocolate (or plain) milk. The carbohydrates in it will help replenish the energy stored in your muscles (called glycogen stores) and aid in muscle recovery—more so than a carb-only drink. Don’t like milk? Substitute with a post-workout snack of banana and peanut butter.