Glycemic index is a measure of how fast a food increases blood sugar. High glycemic index foods include simple sugars and white bread that enter the bloodstream quickly, while low glycemic index foods include whole grains that are digested slowly and trigger more modest increases in blood sugar.
One theory is that rapid increases in blood sugar trigger greater insulin release, which promotes fat storage. British researchers found that middle-aged adults lost more weight following a low glycemic diet than a high glycemic diet during a 12-week study. Both groups reduced caloric intake by 300 calories below normal. The average blood sugar levels was lower in the low glycemic index group, but there were no differences between groups in heart disease risk factors such as blood pressure, cholesterol, or waist circumference. Few studies have found that the glycemic index of the diet influences weight loss or heart disease risk factors in healthy people.