Glycemic index (GI)

Glycemic index (GI) compares the rise in blood glucose over the 2 hours after eating a food with the rise from the same amount of a reference food, usually glucose or white bread, which scores 100.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 201.} Low-GI foods are digested and absorbed slowly, producing smaller rises in blood glucose and insulin.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 202.} The NSCA textbook classifies GI as low at 55 or less, medium at 55 to 69 and high at 70 or more.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 202.} Vegetables, legumes, beans and whole grains tend to have a low GI.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 201.}

A food’s published GI can vary with testing methods, ingredients, ripeness, processing, cooking and storage.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 202.} Portion size and eating carbohydrate as part of a mixed meal also affect the response.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 201.} Glycemic load accounts for portions: multiply GI by the grams of carbohydrate in a serving and divide by 100 for a more realistic gauge.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 202.}

In practice

Before exercise, both low- and high-GI carbohydrates work; research hasn’t shown either to be better.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 218.} For nutrient timing, high-GI foods suit exercise itself for quick energy and the period just afterward to replenish glycogen faster.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 202.}

For everyday eating, the IPTA textbook generally favors slower-digesting complex carbohydrates because they raise blood sugar more gradually.^{4International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 500.} Some studies, though not all, associate lower-GI or lower-glycemic-load diets with lower fasting insulin and fewer cardiovascular risk factors.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 203.}