The Glycemic Index in Sport
Ellen Coleman, RD, MA, MPH © 2004

The glycemic index (GI) provides a way to rank carbohydrate-rich foods according to the blood glucose response following their intake. The GI is calculated by measuring the incremental area under the blood glucose curve following ingestion of a test food (glucose or white bread) providing 50 g of carbohydrate, compared with the area under the blood glucose curve following an equal carbohydrate intake from the reference food. All tests are conducted after an overnight fast (1).

The GI reflects the rate of digestion and absorption of a carbohydrate-rich food. Thus, the GI is influenced by: the food form (including particle size, presence of intact grains, texture, and viscosity); the degree of food processing and cooking; the presence of fructose or lactose (both have a low GI); the ratio of amylopectin and amylose in starch (amylose has a slower rate of digestion); starch-protein or starch-fat interactions; and the presence of antinutrients such as phytates and lectins (1).

Generally, foods are divided into those that have a high GI (glucose, bread, potatoes, breakfast cereal, sports drinks), a moderate GI (sucrose, soft drinks, oats, tropical fruits such as bananas and mangos), or a low GI (fructose, milk, yogurt, lentils, pasta, cold climate fruits such as apples and oranges). Tables of the GI of a large number of foods have been published internationally (2).

Some practitioners have recommended manipulating the GI of foods and meals to enhance carbohydrate availability and improve athletic performance. For example, low GI foods are often recommended before exercise to promote sustained carbohydrate availability. Moderate to high GI foods are recommended during exercise to promote carbohydrate oxidation and following exercise to promote glycogen repletion.

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