Understanding the glycemic index (GI)

The glycemic index (GI) is a scale out of 100 that ranks a carbohydrate-containing food or drink by how fast it raises blood sugar levels after a set amount is eaten. Diabetes Canada recommends people living with diabetes and prediabetes choose lower glycemic index foods and drinks more often to help control blood sugar.

While individual response to carbohydrate-containing foods may vary, typically foods with a high GI create a higher and faster rise in blood sugar than foods with a low GI. There are three categories:

• low GI (55 or less) 

• medium GI (56-69)

• high GI (70 or more)
   

On top of the type of carbohydrate you choose, the quantity or serving size also has a role to play in managing your blood sugar. Even low GI foods need to be eaten in a specific amount or serving size to avoid a high blood sugar response.

The GI of the food can change based on the serving size eaten, cooking method and by combining the food with other ingredients in a meal or snack. By pairing a high GI food with a combination of non-starchy vegetables, lean protein and healthy fats at each meal or snack, you can reduce the overall glycemic response.

While this is a tool to help people living with diabetes better understand blood sugar changes in response to foods eaten, every body is different. You may find that some high GI foods do not impact your blood sugar as much while some low GI foods do!

Aim to eat foods in the low GI category most often as they tend to have less of an effect on blood sugar. Aim to eat foods in the medium category sometimes, and foods in the high GI category the least often. Work with a registered dietitian to find ways to balance meals and snacks and fit all of your usual food choices into a healthy eating pattern that can help minimize impact on blood sugar.

Benefits of a low-glycemic index diet

• Decrease risk of type 2 diabetes.

• Help manage your blood sugar and prevent complications.

• Decrease risk of heart disease and stroke.

• Feel full faster and longer.

Meal planning ideas

Here are some meal planning ideas to lower the overall GI of a meal:

• Cook your pasta al dente (firm). Check your pasta package instructions for cooking time. Remove one minute from the suggested cooking time for al dente. Firm pasta requires more work for digestion, slower the rate the glucose hits your body.

• Make food and drinks such as fruit and unsweetened milk or alternatives part of your meal. These foods often have a low GI.

• Try lower GI grains, such as barley, quinoa, oats and bulgur.

• Swap half of your higher GI starch food serving with beans, lentils or chickpeas. For example, instead of having 1 cup of cooked short grain rice, have ½ cup of cooked rice mixed with ½ cup of black beans. This increases the fibre and protein which helps the starchy food (like rice) digest more slowly and have a lower effect on blood sugar. 

• Cook and cool potatoes, rice, pasta and other grains and enjoy them cold or reheated. This increases resistant starch which is not digested and so has a lower effect on blood sugar.

Using the glycemic index to choose food is just one aspect of healthy eating. Healthy eating also means choosing a variety of foods, having moderate portion sizes, and selecting whole foods more often than overly processed foods.

Also, while the glycemic index can indicate the likelihood of a food’s impact on your blood sugar, we don’t often eat individual foods but rather include them as a part of a healthy meal. Because of this, overall meal planning matters and the GI is just one tool to help individuals make healthy choices for their diabetes management.