By Charles Poliquin
Avoid fructose and high-glycemic carbohydrates prior to strength training to burn more fat. Whether your goal is to gain muscle and build strength, or simply lose fat, you will achieve better results from eating protein, good fat, and low-glycemic foods prior to training. Here’s how it works.
The amino acids will help prevent muscle degradation during training; healthy fats will enhance gene signaling for an anabolic response; avoiding high-glycemic foods will allow the body to burn fat for energy rather than carbs. Meanwhile, you must avoid fructose, especially liquid forms such as high-fructose corn syrup found in energy and sports drinks, because research shows that fructose will inhibit fat burning and favor the use of carbs as your primary energy source. A similar effect occurs when you ingest high-glycemic carbs before training, but the effect is magnified when fructose is present.
For example, a recent study tested how the body uses different substrates, or forms of energy, during exercise depending on what is eaten beforehand. Researchers gave active young men either a low-glycemic meal, a low-glycemic meal with fructose, or a high-glycemic meal without fructose and then had them walk briskly for an hour.
Results showed that the low-glycemic fructose-free group burned primarily fat and fewer stored carbs during exercise. The high-glycemic and low-glycemic w/ fructose groups favored the use of stored carbs for energy, and burned little fat.
Overall, the results indicate that both the glycemic index and fructose content of a pre-exercise meal dictate what source the energy calls on for fuel. Therefore, when doing anaerobic-style training such as weight lifting, best results come from eating protein, smart fats, and possibly some green vegetables at last 45 minutes before your workout.
Endurance athletes will also benefit from avoiding fructose and carbs pre-exercise, assuming their muscle glycogen stores are full since this will preferably shift the body to use up fat, storing glycogen for use later in the workout for greater work capacity.
Take away the following points:
• Avoid fructose and high-glycemic carbs pre-workout.
• A small amount of fructose can be metabolized by the liver, and research suggests the amount the liver can handle is affected by whether you are overweight, insulin resistance, or have diabetes.
• Assuming you are lean and insulin sensitive, research suggests the following use of fructose in is fine:
1) Small amounts of fructose from natural sources (vegetables and fruit), and
2) Refueling post-workout with carbs that include small natural fructose sources, either from veggies, fruit, fruit juice, or a high-quality carb powder that contains a small amount of fruit-derived fructose.
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. Published Ahead of Print.