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Glycemic Index and Endurance Performance

As an athlete, the food you eat has a huge impact on your performance, specifically in endurance events. In terms of carbohydrates, one such factor is the glycemic index; a measure of how quickly certain foods raise your blood glucose. Food with a high glycemic index (>75) will raise blood glucose levels more quickly than food with a low glycemic index (<50). For a diabetic, it is important to stay away from foods that have a high GI, but for an endurance athlete, foods with high GI is one key to long-lasting endurance.

When you exercise, your body immediately begins utilizing its storages for fuel. One of its main sources for energy utilization is the glycogen stored in muscle and liver. If your muscle glycogen stores become depleted you will reach exhaustion. So, the key to maintaining high intensity exercise for a long period of time is to maintain glycogen levels. The most efficient way to do this is to keep blood glucose levels high while exercising; something easily accomplished by consuming food with a high glycemic index. Numerous sources of glycemic indices exist with one being found in our research library.

When you exercise, your body releases hormones that inhibit the release of insulin, the hormone responsible for activating the glucose transporters on the cells of your body. Fortunately, your skeletal muscles have additional glucose transporters that are not dependent on insulin (for more details read how exercise cures non-insulin dependent diabetes). This mechanism ensures that any food consumed during exercise will be shuttled exclusively to skeletal muscle for energy.

If you are shuttling blood glucose into your muscles then you are sparing the breakdown of muscle glycogen. Consuming foods with high glycemic index will ensure that your blood glucose levels stay elevated and that you will be able to exercise longer before reaching exhaustion. For endurance athletes, exogenous (dietary) fuel sources are a necessity for optimal competition.

High glycemic foods are also important for optimal recovery. If you consume food with a high GI immediately after exercise, the glucose will be shuttled preferentially to your skeletal muscle and will be used to help rebuild the glycogen lost during exercise speeding recovery.

Written by Ryan Serrano with Eric Sternlicht, Ph.D. Occidental College, Los Angeles, CA.