Glycemic Index and Exercise Performance

The glycemic index (GI) is a ranking of carbohydrate-containing foods that is based on the food’s effect on blood sugar as compared with a standard reference food’s effect. Though the GI was originally devised to aid diabetics, it is now extensively used in sports nutrition to aid athletes in the selection of appropriate carbohydrates to choose for training. In a 2006 study published in the American Journal of Clinical Nutrition, researchers investigated the effects of meals with different glycemic indexes on the metabolic response during exercise in women. Eight active women participated in two trials. In each trial they received a test breakfast 3 hours before performing a 60 minute run. The first trial consisted of a high-glycemic breakfast, while the second was low-glycemic. Researchers found that the low-glycemic breakfast resulted in a higher rate of fat oxidation during exercise than did a high-glycemic meal. While endurance athletes may require the higher glycemic meal, those individuals desiring weight loss may benefit from consuming lower-glycemic foods prior to exercise.