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 effects that different foods have on blood glucose levels (i.e., blood sugar) vary considerably. The glycemic index or glycaemic index (GI) attempts to measure this variation. It does so by estimating how much each gram of available carbohydrate (total carbohydrate minus fiber) in a food raises a person's blood glucose level following consumption of that food, relative to consumption of pure glucose (the defining standard), which has a glycemic index of 100. Because a large increase in the glucose response to a food typically makes for a steeper initial climb in that response, it is also a rough measure of how quickly blood glucose levels may rise after eating a particular food, though this rapidity can be influenced by the quantity of fat eaten with the food, as well as by other factors.

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, 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.

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.


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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.