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The glycemic index measures how quickly a source of carbohydrate is digested and absorbed into the bloodstream. Glycemic indices can be determined in a lab setting by measuring the blood sugar concentrations of study participants over hours after having consumed a particular carb source; values are ranked on a scale of 0 (lowest) to 100 (highest). Quickly digested carbohydrate sources cause a rapid spike in blood sugar resulting in a high glycemic index value. Slowly digested carbohydrate sources cause more gradual and sustained elevations in blood sugar and therefore have lower glycemic indices. Table 5.2 lists some example glycemic index values.

Table 5.2 A list of some example carbohydrate sources and their glycemic index values.

Glycemic Index Values
Pure dextrose (glucose) powder	100
Gatorade	90
Plain white potato (average of all cooking methods)	85
Cocoa Puffs cereal	75
White bagel	70
White rice	65
Sweet potato	60
Quinoa	55
Oatmeal	55
Whole-grain bread	50
Brown rice	50
All-Bran cereal	45
Pasta (higher glycemic index the longer you boil it)	30-50
Oranges, peaches, pears, apples, carrots	40
Kidney beans	35
Skim milk and low-fat yogurt	30
Grapefruit	25
Soybeans, chickpeas	15
Hummus dip	5
Pure insoluble fiber	0

Processed carbohydrate sources often have a higher glycemic index value compared to whole food counterparts because the processing of food can break it down, making it more quickly and easily digested. On the other hand, glycemic index values are lower in the presence of fat, protein, or fiber, which can slow digestion. For this reason, hummus, the processed version of chickpeas with added fats, has a lower glycemic index than chickpeas themselves. It is also important to note that eating other food sources along with a particular carbohydrate source can effectively alter its glycemic index by slowing digestion. Glycemic index values affect nutritional recommendations for body composition and performance in several ways, as detailed in the following.