The Glycemic Index and It's Applications to Performance

For hard training athletes of all levels, every nutritional angle must be optimized for optimal performance. Specifically, the glycemic index (GI) can play a very important role in energy levels and overall health, so it seems prudent to learn how to manipulate the GI to our greatest performance advantage.

What is the glycemic index? "A numerical index given to a carbohydrate rich food that is based on the average increase in blood glucose levels occurring after the food is eaten." For example, if someone eats a carbohydrate with a numerical value of 25 from a particular source, the GI score of the glycemic response would indicate that this food rose blood glucose levels to 25% of what they would have been raised compared to the standard (glucose). Various foods contain carbohydrates that will raise blood sugar to different levels. There are also factors which affect the GI score of foods such as fiber, protein, and fat content. For example, a slice of whole grain bread will digest more slowly than a slice of white bread because of the fiber content of the whole grains. If peanut butter was added to the bread, digestion rate would be even slower because of the fat and protein content.

Since we already know that carbohydrates are essential to good exercise performance and we also know that not all carbohydrates are created equal in terms of their structure, it becomes important to figure out when to eat what kinds of carbohydrates and in what amounts so that we understand the glycemic index and its applications to performance. There are a couple of times during the day when nutrition plays a particularly important role for the athlete and those times are before, during and after exercise.

In the hour before exercise, carbohydrates that are high on the glycemic index are not as advantageous to athletes; they produce a large insulin spike which produces a burst of energy followed by a subsequent crash, thereby causing rebound hypoglycemia. This causes central nervous system impairment during exercise which can be be detrimental to exercise performance. Additionally, high GI carbohydrates when taken pre-workout, inhibit lypolysis and contribute to premature glycogen depletion and fatigue. As stated in one source, "The ideal meal immediately before exercising should provide a source of glucose to maintain blood sugar and muscle metabolism with minimal increase in insulin release."

With this in mind, what kind of carbohydrates will give us these ideal conditions? Ones that score low on the glycemic index! Eating a food such as oats or brown rice with minimal fats in a pre-workout meal is an excellent way to improve performance by providing good energy levels and steady blood sugar. During other times of the day, complex carbohydrates that are low on the glycemic index will encourage good glycogen replenishment and excellent energy. Eating complex carbohydrates frequently helps to keep blood glucose levels stable, and also prevents insulin spikes, not to mention the fact that it is more healthy.

On the flip side, there is also a time when simple carbohydrates that are high on the glycemic index are very appropriate and those of the complex nature are not be as advantageous. The time being referred to is immediately following an anaerobic workout. At these times, a sudden spike in insulin will help to jump start glycogen loading and the shuttling of nutrients and protein into muscles for much faster recovery. It will also help the athlete to feel mentally energized after the workout even though his/her muscles may feel tired. Carbohydrates with low GI scores would not be as beneficial at this time due to the fact that they break down more slowly.

Carbohydrate intake during exercise can also be something that an athlete can use to their advantage. During prolonged exercise of more than approximately two hours, a simple carbohydrates high on the GI such as glucose, waxy maize or maltodextrin ingested at a rate of approximately 1 gram per minute can help keep energy levels high and fatigue relatively low for endurance athletes. In strength athletes and bodybuilders, it can accomplish the same thing, but a carbohydrate drink such as glucose during a workout can also help to keep cortisol and other catabolic hormones low. This is significant because it can maximize the anabolic hormonal environment of the athlete and greatly aid efforts go gain muscle mass and strength.

Knowing how to use carbohydrates within the framework of the glycemic index as a tool for exercise performance can be extremely key for high performing athletes. Not only in how an athlete may feel physically, but more importantly in performance enhancements that are achieved. It behooves the competitor to learn how to use the glycemic index in a way that can help them.