Glycemic Index

Eating right can lower your blood sugar, LDL-cholesterol, and triglyceride levels. Healthy foods in the right amounts can help to keep your glucose levels stable, too, and slow or prevent diabetes complications. The glycemic index (GI) classifies carbohydrates based on how quickly and how much they boost blood sugar compared to pure glucose. Choose low-GI foods are best for keeping blood sugar levels down.

The glycemic index or glycaemic index (GI) (/ɡlaɪˌsiːmɪk ˈɪndeks/) is a number associated with a particular type of food that indicates the food's effect on a person's blood glucose (also called blood sugar) level. A value of 100 represents the standard, an equivalent amount of pure glucose.

The GI represents the rise in a person's blood sugar level two hours after consumption of the food. The glycemic effect of foods depends on a number of factors, such as the type of starch, physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal. The GI is useful for understanding how the body breaks down carbohydrates and takes into account only the available carbohydrate (total carbohydrate minus fiber) in a food.

The glycemic index is usually applied in the context of the quantity of the food and the amount of carbohydrate in the food that is actually consumed. A related measure, the glycemic load (GL), factors this in by multiplying the glycemic index of the food in question by the carbohydrate content of the actual serving. Watermelon has a high glycemic index, but a low glycemic load for the quantity typically consumed. Fructose, by contrast, has a low glycemic index, but can have a high glycemic load if a large quantity is consumed.

GI tables are available that list many types of foods and their GIs. Some tables also include the serving size and the glycemic load of the food per serving.

A practical limitation of the glycemic index is that it does not measure insulin production due to rises in blood sugar. As a result, two foods could have the same glycemic index, but produce different amounts of insulin. Likewise, two foods could have the same glycemic load, but cause different insulin responses. Furthermore, both the glycemic index and glycemic load measurements are defined by the carbohydrate content of food. For example, when eating steak, which has no carbohydrate content but provides a high protein intake, up to 50% of that protein can be converted to glucose when there is little to no carbohydrate consumed with it. But because it contains no carbohydrate itself, steak cannot have a glycemic index. For some food comparisons, the "insulin index" may be more useful.

The material on this site is for informational purposes only and is not intended as medical advice. It should not be used to diagnose or treat any medical condition. Consult a licensed medical professional for the diagnosis and treatment of all medical conditions and before starting a new diet or exercise program. If you have a medical emergency, call 911 immediately.