A low-glycemic diet is one that selects foods on the basis of minimal alteration of circulating glucose levels. Glycemic index (GI) and glycemic load (GL) are measures of the effect on blood glucose level after a food containing carbohydrates is consumed. Glucose is one of the body's main sources of energy; it is the fuel used by the brain, muscles, and other organs. Glucose is set at 100, and all foods are indexed against that number. Low GI foods affect blood glucose and insulin levels less and have a slower rate of digestion and absorption.