What is the glycemic index (GI)?

Reza Yavari, MD
Endocrinology Diabetes & Metabolism

The glycemic index (GI) refers to the way sugar-rich foods are digested in the body; it depends on how different foods are absorbed and the combinations of foods ingested together. Watch endocrinologist Reza Yavari, MD, explain glycemic index.

Glycemic index is used to describe a carbohydrate’s effect on blood glucose. Foods with a low glycemic index (multigrain foods, for example) take longer to digest and therefore increase blood glucose more slowly. Foods with a high glycemic index, such as sweets and refined sugar, quickly increase blood glucose.

(This answer provided for NATA by the Appalachian State University Athletic Training Education Program.)
RealAge
Administration
When you place an increased energy demand on your body through exercise, your body will use the sugar (glucose) in your blood and the stores of glycogen in your liver and muscle tissues to help meet that demand. How a particular food will affect those energy sources depends on its glycemic index (GI). The glycemic index is used for carbohydrates only and is a ranking that reflects the amount of change a food causes in blood sugar levels.

For example, foods with a high glycemic index, such as sugary treats and potatoes, cause a rapid increase in blood glucose that leads to a sudden burst in energy, albeit one that drops off again fairly quickly. On the other hand, foods with a low glycemic index, such as bran flakes and kidney beans, cause a more gradual increase in blood glucose, which results in longer-lasting energy. In general, foods with a low or medium GI are better for you than high-GI foods.

The glycemic index works on a scale of 1 to 100, with 1 being the lowest and 100 being the highest. Carbohydrates are broken down into three GI categories: low, medium, and high.
 
Johns Hopkins Medicine
Administration
The glycemic index (GI) is a measure of the ability of carbohydrates to increase blood glucose levels, which can lead to weight gain and diabetes. Foods with a low GI cause blood levels to increase more slowly, thus avoiding spikes in glucose which are unhealthy and contribute to weight gain.

Foods with GI are usually refined (like white bread and white rice) or contain high fructose corn syrup. Although some say “sugar is sugar”, that’s really not the case with high fructose corn syrup -- it can lead to fat accumulation in the liver and other areas.

Proteins and whole grains, which are rich in fiber, digest more slowly -- leaving you fuller longer and keeping glucose levels stable. This promotes weight loss and helps keep diabetes at bay. A diet rich in whole grains and low in refined carbs is important whether or not weight loss is your goal.
Janis Jibrin, MS, RD
Nutrition & Dietetics
A few thousand high-carbohydrate foods have been ranked on a scale from 1 to 100 according to how quickly they raise blood sugar; this ranking is called the glycemic index (GI). This was done by giving people a fixed amount -- usually 50 grams -- of a carbohydrate-containing food, such as carrots or an English muffin, and watching how high their blood sugar rose over the course of two hours. That increase was compared to the effects of eating plain glucose, which has a GI of 100. The glycemic index was developed to help people with diabetes choose foods that would cause a slower and smaller rise in blood sugar. The idea is that if you choose low-GI foods, then your blood sugar will be better controlled.
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The glycemic index is a numerical value between 0 and 100 that classifies how the carbohydrates in individual foods affect blood-glucose levels. Foods with a high glycemic index contain carbohydrates that cause a dramatic rise in blood-glucose levels. Foods with a low glycemic index contain carbohydrates that do not increase blood-glucose levels that much. To obtain these values, the effects of these foods are compared to that of healthy individuals ingesting pure glucose. If you have diabetes, the glycemic-index values can help you make better food choices to prevent your blood glucose from rising too high and too fast.
Harris H. McIlwain, MD
Rheumatology
There are findings from Harvard indicating that you can use the glycemic index to choose carbohydrate foods that will have a relatively low impact on your blood sugar. This index is a numerical system that ranks carbohydrates on a scale of 0 to 100, according to their effect on blood glucose (sugar) levels. In the Harvard studies, scientists measured the amount of sugar that different foods put into the body right after they were ingested. Foods that gave a sugar "boost" appeared to increase weight gain and obesity, as well as added to the risk of getting heart disease and diabetes. These studies reported that foods pure in protein and fat (such as meat, chicken, and fish) have a glycemic index of zero. A baked potato has a glycemic index of 85. 

A food low on the glycemic index (meat, chicken, fish, soy products, and some vegetables) will cause a small rise in blood sugar; a food high on the glycemic index (the baked potato and other starchy foods) will trigger a more dramatic rise, which can cause an increase in appetite.
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Jacob Teitelbaum
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The glycemic index (GI) tells you which foods raise your blood glucose fastest and highest. This is especially important for sugar addicts to keep in mind. Pure glucose gets a GI score of 100-all other foods are measured in relation to glucose. A food with a glycemic index over 85 raises blood sugar rapidly, but a food with a glycemic index under 30 does not raise blood sugar much at all. You also need to take portion size into account, of course. The term glycemic load combines these factors.
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The glycemic index (GI) measures how a carbohydrate-containing food raises blood glucose. Foods are ranked based on how they compare to a reference food -- either glucose or white bread. A food with a high GI raises blood glucose more than a food with a medium or low GI.
Michael T. Murray, ND
Naturopathic Medicine

The glycemic index (Gl) is a numerical scale used to indicate how fast and how high a particular food raises blood glucose (blood sugar) levels. There are two versions of the GI, one based on a standard of comparison that uses glucose scored as 100; the other is based on white bread. Foods are tested against the results of the selected standard. Refined sugars, white flour products, and other sources of simple sugars are quickly absorbed into the bloodstream, causing a rapid rise in blood sugar. In response, the body boosts secretion of insulin by the pancreas. High-sugar junk food diets definitely lead to poor blood sugar regulation, obesity, and ultimately type 2 diabetes. And, because of the stress on the body that they cause, including secreting too much insulin, they can also promote the growth of cancer and increase the risk of heart disease. Our simple recommendation? Don't eat &quotjunk foods," and pay attention to the glycemic index of food that you eat.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.