Athletes need energy. And the primary fuel for muscles is glucose. Fat can provide additional energy, but that depends on the individual athlete's ability to mobilize and utilize fat. In general, muscles prefer glucose. Easily digested carbohydrate foods can provide a fast burst of glucose to fuel working muscles.
But what about pre-event eating? Are easily digested carbs the best choice? Some research shows that pre-event eating should emphasize less-digestible carbohydrate foods. Those foods can be described as "low GI," meaning the foods have a low-glycemic index score.
What's the Glycemic Index?
In the early 1980s, a nutrition professor in Canada invented the glycemic index.
It was originally intended to help people with diabetes manage their carbohydrate intake. Foods are given scores, based on their effect on blood glucose. Foods with high scores cause glucose to rise quickly. Foods with low scores don't raise glucose much, and theoretically those would be preferable for diabetics. The scores are created like this:
- Bread, which was chosen as the standard, has a GI score of 100.
- 10 volunteer subjects are given portions of various foods that contain 50 grams of carbohydrates.
- Blood samples are taken every 15 minutes for 1 hour; then every 30 minutes for a total of 2 hours.
- The changes in blood glucose are graphed.
- The GI score is calculated using the area under the glucose curve.
- The lower the score, the less the glucose rise.
Critics of the GI scoring system argue that no one eats single foods like this in a laboratory setting. People eat mixed meals, and fat, protein and fiber all slow carbohydrate digestion and absorption.
Unfortunately, the GI scoring system can make junky food look healthy. Potato chips have a lower GI score than plain baked potatoes; M&Ms have a lower score than watermelon; a Snickers bar has a lower score than plain rice. Why? Because potato chips, Snickers and M&Ms contain fat that slows digestion.
Why Low-GI Foods Are Good for Athletes
There's evidence that low GI pre-event foods benefit athletes. Instead of a quick rush of glucose from a high-GI food, a low-GI food provides a slow, steady supply of muscle fuel.