Research shows that eating low-glycemic index snacks, such as a small handful of nuts (which have the ideal combination of unsaturated fat, protein and carbs), can increase fat burn during exercise. Other low-GI snacks include beans, oatmeal, apples, eggs, and other low-sugar, high-protein and/or fiber snacks.
Why? Low-GI carbs will make your blood glucose rise slowly, triggering a lower insulin response, whereas high levels of insulin may actually limit fat burning – not exactly what you want when you’re about to spend your morning at the gym!
The study published in the European Journal of Applied Physiology showed that even pairing low GI snacks with something sugary is a bad idea; a high fructose content may negate the benefits. So, for maximum fat burning power skip the fruit dip and try spreading a little peanut butter on those apple slices in the morning, and avoid topping your oatmeal with dried cranberries and other sugary mix-ins. Keep it clean and simple, at least until after your workout!
Reference: Sun, F., Wong, S., et al. Substrate Utilization During Brisk Walking is affected by Glycemic Index and fructose Content of a Pre-Exercise Meal. European Journal of Applied Physiology. November 2011.