What GI values of foods can tell you about their impact on blood sugar
Debra Manzella, MS, RN, is a corporate clinical educator at Catholic Health System in New York with extensive experience in diabetes care.
Do-Eun Lee, MD, has been practicing medicine for more than 20 years, and specializes in diabetes, thyroid issues and general endocrinology. She currently has a private practice in Lafayette, CA.
The glycemic index (GI) is a relative ranking of how different carbohydrates affect blood sugar. When you have type 2 diabetes, one of the best ways to control your glucose levels is to eat foods that don’t cause major blood sugar (glucose) spikes.
Knowing the glycemic index of the carbohydrates you eat can help you fine-tune your meals to keep your blood sugar within a normal range. Foods with a higher GI value are more likely to spike your blood sugar than foods with a lower GI.
This article explains the glycemic index and how it works. It also provides glycemic index charts that show low GI, moderate GI, and high GI carbohydrates.
The GI is a rating system that ranks carbohydrates on a scale of 1 to 100 based on how much they raise blood sugar.
Processed foods such as candy, breads, cake, and cookies have a high GI, while whole foods such as unrefined grains, non-starchy vegetables, and fruits tend to have a lower GI.
Carbohydrates with a low GI value are digested, absorbed, and metabolized more slowly than their high-GI counterparts. They typically cause a lower and slower rise in blood glucose and, subsequently, insulin levels as well.
The GI values can be broken down into three ranges. Remember that a low GI is a food that won't raise your blood sugar as much as a food with a medium or high GI.
For example, rice milk (a processed food without any fiber) has a high GI of 86, while brown rice (plenty of fiber) has a medium GI of 66.
The index values are created by a rigorous testing process. Ten or more people each eat 50 grams of the same digestible carbohydrate (the test food), then researchers measure each individual's glucose response two hours after consumption, plot the points on a graph, and measure the area under the curve (AUC) of their glucose response.
At a separate date, the same 10 people consume 50 grams of pure glucose (the reference food), and researchers again measure each person's glucose response AUC two hours after consumption.
The GI value of the test food is then calculated by dividing the glucose AUC for the test food by that of the reference food for each person. The final GI value is an average of those 10 numbers.
Ultimately, the GI value is the average person's blood sugar response to a specific carbohydrate. Note that individual responses may vary based on other factors.
Critics of the GI system state that the index doesn't take into account how much food is being eaten or its other nutritional qualities (or lack thereof), such as protein, fat, vitamins, minerals, and antioxidants. As the GI looks strictly at the carb count, basing a diet around these numbers means you would be ignoring a lot of other helpful information to determine the true health value of a food.
To counteract the quantity issue, researchers developed the glycemic load (GL) measurement, which accounts for the quantity of the food being eaten. The glycemic load looks at both the quality and the quantity of the carb.
Glycemic load is calculated by multiplying the GI value by the number of carbohydrates (in grams), then dividing that number by 100.
For example, an apple has a GI of 40 and contains 15 grams of carbs. (40 x 15)/100 = 6, so the glycemic load of an apple is 6.
Like GI values, GL values can also be broken down into three ranges:
Since it's carbohydrates that raise blood sugar, understanding GI can help you figure out which foods are best for glucose management.
Among the benefits of following the GI list when planning your meals:
The glycemic index may not work for everyone and it falls short in a few ways. These include:
The American Diabetes Association states that carbohydrate amounts (grams of carbohydrates) and available insulin may be the most important factors influencing blood sugar response after eating and should be considered when developing an eating plan.
The most reliable way to assess how your body is affected by certain foods is to test your blood sugar two hours after a meal.
For most people, an ideal blood sugar result is less than 180mg/dL two hours after the start of a meal. If you are not sure of what your target blood sugar should be, discuss it with your physician.
Referencing the GI of foods can be useful, but it shouldn't be the only tool you use to help control blood sugars.
The glycemic index should be used as an adjunct to carb counting and lifestyle changes, such as eating an overall balanced diet, practicing good portion control, and exercising regularly.
The glycemic index (GI) measures how much a specific food's carbohydrate affects blood sugar; since foods like meat and butter don't contain carbohydrates, they are not included.
Some good food choices low on the glycemic index include most vegetables and fruits, nuts, minimally processed grains, and pasta (both regular and whole grain). A low GI is considered 55 or less.
Some foods with a high glycemic index include white bread, potatoes, and white rice. This is due to these foods containing a lot of starches, which are rapidly broken down by the body to cause a rise in blood glucose. For this reason, many processed foods or soft drinks are also high on the GI sclae.
Glycemic Index Foundation. About the glycemic index.
Glycemic Index Foundation. What is low GI?
The University of Sydney. About the glycemic index.
Willett W, Liu S. Carbohydrate quality and health: distilling simple truths from complexity. Am J Clin Nutr. 2019;110(4):803-804. doi:10.1093/ajcn/nqz215
Glycemic Index Foundation. Glycemic Load.
Centers for Disease Control and Prevention. Diabetes meal planning.
American Diabetes Association. Carb counting and diabetes.
American Diabetes Association. 6. Glycemic targets: Standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1): S83–S96. doi:10.2337/dc22-S006
Harvard Health Publishing. A good guide to good carbs: The glycemic index.
National Health Service (NHS). What is the glycaemic index (GI)?
American Diabetes Association. 5. Facilitating behavior change and well-being to improve health outcomes: standards of medical care in diabetes—2021. Dia Care. 2021;44(Supplement 1):S53-S72. doi:10.2337/dc21-S005
Shukla A, Iliescu R, Thomas C, Aronne L. Food order has a significant impact on postprandial glucose and insulin levels. Diabetes Care. 2015; 38(7):e98-e99. doi:10.2337/dc15-0429
Debra Manzella, MS, RN, is a corporate clinical educator at Catholic Health System in New York with extensive experience in diabetes care.
Thank you, {{form.email}}, for signing up.
There was an error. Please try again.