Sports Performance and Glycemic Index

For some considerable time now, athletes have been warned of the dangers of eating high carbohydrate foods immediately prior to competition. These warnings are based on the facts that the body's response to increased blood sugar levels is insulin production. This may alter the metabolism during exercise by increasing the rate at which the muscles burn carbohydrates as fuel.

As a result of this increased carbohydrate oxidation, hypoglycemia (low blood glucose levels) may occur for a short period. It is this effect that concerns athletes, as it may result in a drop in performance. Coaches and athletes alike talk about avoiding this 'rebound hypoglycemia'.

Some studies have shown that occasional athletes suffer the ill-effects of rebound hypoglycemia, but mostly there is no problem. Even if hypoglycemia does occur after consumption of high-carbohydrate foods prior to sports performance, its duration is brief and its impact minimal. Nevertheless, when a study was published finding that low glycemic index (GI) foods consumed prior to exercise translated to increased performance in comparison with high GI foods, people were quick to jump on the bandwagon.

The thinking is that low GI foods have a more subtle effect on blood glucose levels and the insulin production response, and thus the benefits of consuming carbohydrates prior to exercise (namely, increased fuel stores) is not negated by a subsequent intense insulin production response. Many sports nutrition articles are now recommending that endurance athletes choose low GI foods such as lentils prior to sports competition.

Sadly, though, it appears as though this advice has been premature. Subsequent studies have reported that any benefits reaped due to the consumption of low GI foods prior to exercise are minimal and short lived. Further, it has been forgotten that endurance athletes generally replenish their carbohydrate and fluid stores through consumption of high GI foods and drinks during performance of their sport.

One study has now shown that consumption of large quantities of carbohydrates during exercise has the effect of meeting the continuing energy requirements of athletes as well as overriding any effects from the type of pre-event meal. Thus, athletes should not be  concerned about the glycemic index ratings of their pre-event meals, but should be confident that consuming appropriate amounts of carbohydrates will put them in the best position to perform optimally in their sport. They may feel free to choose their menu according to their own preferences and experience.

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