With diabetes, a controlled diet is one of the most important factors to maintain normal glucose (blood sugar). The glycemic index (GI) was developed as a research tool to examine how blood glucose is affected by foods that contain carbohydrates. 

The glycemic index ranks food with a value based on how quickly that food is converted to sugar in the blood and how fast the glucose returns to normal.

Foods with a high GI score are digested and absorbed by the body more quickly, causing a rapid rise in blood glucose. Some research has found diets with a high glycemic load to be a risk factor for type 2 diabetes. Foods with a low GI score are converted to sugar more slowly and do not cause a rapid spike in blood glucose. 

GI scores should not be confused with how nutritious a particular food is. The score is ranked solely for the rate at which it raises glucose levels.

In general, refined starches and sugars have a high GI, legumes and whole grains have a moderate GI, and many fruits and vegetables have a low GI. As with fats, scientists categorized foods as “good” and “bad” carbohydrates. In theory, people with diabetes should choose more of the low-glycemic foods at meals to keep glucose levels stable. Using the glycemic index for meal planning, however, is complicated, and it may not adequately control glucose.

Certain factors may change the final GI score of a food depending on how it is prepared and its reaction with other foods. In addition, the GI of a specific food may vary from individual to individual, and many foods do not have a GI, which can make it difficult to plan a meal using the glycemic index as a guide. It is important to note the GI of a food eaten alone may change when added to a meal.

Although some scientists believe that a low-glycemic diet may help control glucose and fat (lipids) in people with diabetes, the results are inconclusive. There is not enough evidence of long-term benefits to recommend use of the glycemic index for diabetic care. The glycemic index can be used in meal planning but should not be the only consideration when making food choices. According to the American Diabetes Association, for people with diabetes, foods may have a different GI than stated, from day to day, based on the individual’s glucose reading and insulin resistance.

The use of low-GI diets remains controversial in the treatment of diabetes. If a person with diabetes is interested in using the glycemic index for dietetic reasons, this should be done with the assistance of a physician or registered dietitian.