Glycemic Index and Exercise Performance

When it comes to talking about carbohydrates and their role in enhancing performance, it seems all carbohydrates may not be the same. Even distinguishing between sugars and starches may not be enough. Glycemic index of a food represents how quickly a food is digested and how high your blood glucose (or blood sugar) will rise after you consume that food. The higher the glycemic index, the higher the rise in blood sugar. To accurately test the glycemic index of a food, one would need to ingest a small serving of a carbohydrate food, and then measure the glucose in the blood over a two hour period. The glycemic index is given in terms of a percentage. Pure glucose results in the highest glycemic index: 100%.

So, if a food results in a glycemic index of 80, this indicates that eating a small serving of that particular food results in a rise of blood sugar which is 80% as great as consuming the same amount of pure glucose. There are many factors that can influence the glycemic index of a food. These include: the structure of the carbohydrate, the absorption rate, what and when you ate previously, and other substances within that food, like the amount of protein and fat.

So, how can this affect athletic performance?

If athletes consume lower glycemic index foods throughout the day and up to 1 1/2 hours before sports activity, they might experience the following positive effects: 1) they might not have a drop in blood sugar prior to training/competition; 2) they might have a higher concentration of fat in the blood to use for energy which will then "spare" their muscle glycogen (stored carbohydrate); "sparing" muscle glycogen usually results in less fatigue and better performance. Conversely, consuming moderate to high glycemic index foods after exercise might help to promote muscle glycogen storage, which is good, since muscle glycogen is required for energy.

Here is a list of some high glycemic index foods (greater than 70%):

waffles, bagels, white bread, rice cakes, graham crackers, Cheerios, watermelon, baked potatoes, mashed potatoes, carrots, jelly beans, Life Savers, honey.

Here are some moderate glycemic index foods (50% to 70%):

orange juice, Gatorade, rice, oatmeal, Grape Nuts, wheat crackers, whole wheat bread, pineapple, raisins, bananas, grapes.

Here is a list of some low glycemic index foods (less than 50%):

Whole meal pasta, peas, chick peas, lentils, baked beans, peanuts, pears, oranges, sweetened yogurt, apple juice, skim milk.

* depending on digestibility, low glycemic index foods may be able to be consumed up to 30-60 minutes before sports activity.

To Summarize: High glycemic index foods may enhance performance in athletes and can be useful during and after work-outs or competitions. Low glycemic index foods may be helpful prior to sports activity. However, research is controversial; so, high and low glycemic index foods may not be beneficial for all athletes. If student-athletes want to "experiment" with different types of carbohydrates, encourage them to do so during practices not competition.

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