What Is the Glycemic Index?

image for breakfast article Glucose is the chemical name of the sugar molecules in your blood. All the carbohydrates, starches, and sugars that you eat are digested or changed into glucose in your body. The amount of glucose in your blood at any given time is called blood glucose. It is important for your health to keep your blood glucose within a specific range.
If you have diabetes, you know how important a healthy diet is for managing your blood glucose levels. A healthy diet, along with medication and regular physical activity, can help keep your glucose levels in check. Following the glycemic index may be one way for you to achieve it.

Understanding the Glycemic Index

The glycemic index is an indirect measure of how much carbohydrate there is in a food. The glycemic index of a particular food is measured by how much it raises blood glucose levels compared to a reference food—usually glucose or white bread. A food with a high glycemic index raises blood glucose levels more than a food with a low glycemic index.
Determining the glycemic index of a food is not as easy as it sounds. Many factors come into play, like ripeness. For example, ripe bananas have a higher glycemic index than unripe. This is because sugar is produced as fruit ripens, making it sweeter. Other considerations include how a food is cooked or what else is eaten along with the food. Generally speaking, foods that are high in fiber have a lower glycemic index, and foods that are highly processed have a higher glycemic index.
Here is how some common foods compare:
Low Glycemic Index (55 or less) Medium Glycemic Index (56-69) High Glycemic Index (70 or higher)
100% stone-ground whole wheat bread Whole wheat or rye bread White bread or bagel
Oatmeal (rolled or steel-cut) Quick oats Short-grain white rice
Pasta, barley Brown or basmati rice Pretzels, popcorn
Sweet potato, corn, yam, legumes, lentils Couscous Pineapple

The Glycemic Index and Diabetes

A lot of research has been done to determine if glycemic index is a useful tool for managing diabetes. So far, the evidence is weak that a low glycemic index diet reduces HbA1c (the measure of glucose levels over the past 2-3 months) or improves glucose level control. But that does not mean that the glycemic index is useless. There are still ways you can use the glycemic index to your advantage.
The glycemic index can be helpful in fine-tuning your food choices. For example, if you want to eat a high glycemic index food, like a ripe banana, balancing your meal with a low glycemic index food, like steel-cut oats, can help to keep your glucose levels in check. But monitoring the glycemic index of your food choices should not take the place of eating a variety of healthy foods. It is also important to remember that portion size plays a role in managing blood glucose.

Counting Carbs Instead

For most people with diabetes, the key to managing blood glucose is carbohydrate counting. Balancing your carbohydrate intake with physical activity and medication can keep your glucose levels under control. Together, counting carbs and monitoring glycemic index may be helpful in managing blood glucose. For instance, knowing how you respond to high or low glycemic index foods can help you plan your carbohydrate intake and avoid fluctuations in your blood glucose levels. Spreading your carbohydrate intake over the course of the day can also help keep your glucose levels steady.

Is the Glycemic Index for You?

Even though knowing the glycemic index of a food might help you predict how your blood glucose levels will respond, it may not be the answer to all your dietary questions. For one thing, the numbers listed above are not set in stone. The glycemic index of a food will be different for each person who eats it, based on their activity level, age, and how quickly the food is digested. Accounting for all these different factors can be complicated, and health professionals agree that patients are less likely to stick with complicated meal plans. So, while the glycemic index might be helpful, it probably will not be the only consideration. Consider discussing your concerns with your doctor or dietitian.


American Diabetes Association  http://www.diabetes.org 
Joslin Diabetes Center  http://www.joslin.org 


Diabetes Canada  http://www.diabetes.ca 
Public Health Agency of Canada  http://www.phac-aspc.gc.ca 


Dietary considerations for patients with type 2 diabetes. EBSCO DynaMed Plus website. Available at:  http://www.dynamed.com/topics/dmp~AN~T270045/Dietary-considerations-for-patients-with-type-2-diabetes  . Updated February 7, 2017. Accessed May 8, 2017.
Dietary guidelines for Americans 2015-2020. Office of Disease Prevention and Health Promotion website. Available at: https://health.gov/dietaryguidelines/2015/guidelines. Updated December 2015. Accessed May 8, 2017.
Glycemic index and diabetes. American Diabetes Association website. Available at: http://www.diabetes.org/food-and-fitness/food/what-can-i-eat/understanding-carbohydrates/glycemic-index-and-diabetes.html Updated May 14, 2014. Accessed May 8, 2017.
The glycemic index and diabetes. Joslin Diabetes Center website. Available at: http://www.joslin.org/info/the%5Fglycemic%5Findex%5Fand%5Fdiabetes.html. Accessed May 8, 2017.
Sadovsky R. Dietary management in patients with type 2 diabetes. Am Fam Physician. 2000;61(2):507-508.

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Article written by Kerr SJ