What Is the Glycemic Index?

image for breakfast article The glycemic index is a number assigned to foods based on how they raise blood glucose values. Glucose is the chemical name of the sugar molecules in blood. All the carbohydrates (carbs), starches, and sugars that a person eats are digested or changed into glucose in the body. The amount of glucose in the blood at any given time is called blood glucose.

People with diabetes know that managing glucose levels is an important part of a healthy diet. Following the glycemic index can help.

Understanding the Glycemic Index

The glycemic index is a measure of how many carbs a food has. Each 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.

Finding out the glycemic index of a food is not as easy as it sounds. There are many factors that affect it, such as 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 factors may be how a food is cooked or what else is eaten with it. Most often, foods that are high in fiber have a lower glycemic index, and foods that are highly processed have a higher glycemic index.

Here are how some common foods compare:

Low Glycemic Index (55 or less) Medium Glycemic Index (56 to 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

The glycemic index can be helpful in fine-tuning food choices. For example, a person with diabetes could balance a high glycemic index food with a low glycemic index food to keep glucose levels in check. But monitoring the glycemic index should not take the place of eating a variety of healthy foods. It is also important to pay attention to portion sizes.

Counting Carbs Instead

Most people with diabetes manage blood glucose by carb counting. This is done along with medicine and exercise. Monitoring the glycemic index may help even more. For instance, knowing how a person responds to high or low glycemic index foods can help that person plan their carb intake and avoid big changes in blood glucose levels. Spreading out carb intake over the course of the day can also help keep glucose levels steady.

Is the Glycemic Index for You?

Knowing the glycemic index of a food may help a person predict how their blood glucose levels will change. But, it might not be the answer to all of a person's dietary questions. For example, the glycemic index of a food will not be the same for each person who eats it, based on their activity level, age, and how quickly the food is digested. These factors can be hard to understand and make it less likely that a person will stick with a difficult meal plan. So, while the glycemic index might be helpful, it probably will not be the only factor to consider.


American Diabetes Association

Joslin Diabetes Center


Canadian Diabetes Association

Health Canada


American Diabetes Association. Standards of medical care in diabetes - 2020. Diabetes Care. 2020 Jan; 43 (Suppl 1):S1-S212.

Dietary considerations for patients with type 2 diabetes. EBSCO DynaMed website. Available at:https://www.dynamed.com/management/dietary-considerations-for-patients-with-type-2-diabetes. Accessed August 21, 2020.

Dietary guidelines for Americans 2015-2020. Office of Disease Prevention and Health Promotion website. Available at: https://health.gov/dietaryguidelines/2015/guidelines. Accessed August 21, 2020.

What is glycemic index? Eat Right—American Academy of Nutrition and Dietetics website. Available at: https://www.eatright.org/food/nutrition/dietary-guidelines-and-myplate/what-is-glycemic-index. Accessed August 21, 2020.

Last reviewed March 2020 by EBSCO Medical Review BoardDianne Scheinberg Rishikof MS, RD, LDN  Last Updated: 3/2/2021