Glycemic index and blood glucose
Struggling with controlling your blood glucose? Learn how to use the glycemic index.
According to Harvard Medical School, “[t]he glycemic index (GI) is a value assigned to foods based on how quickly and how high those foods cause increases in blood glucose levels.” Foods that contain a high GI cause blood sugar levels to increase quickly while foods with a low GI slowly release sugar into the blood creating a slower absorption of food and a feeling of fullness longer. Glycemic index attempts to demonstrate how foods with the same amount of carbohydrates behave differently in the body and that all carbohydrates do not react equally.
GI is determined by having a healthy person eat one food and calculating how fast the sugar enters the blood two hours after ingesting. It compares the response that your body has, after eating the food, to a similar weight of glucose. Foods are then assigned a number value, which is put into a range of low or high ranking. According to the Cleveland Clinic, foods ranked less than 50 are considered to have low GI, whereas foods measuring 51 through 100 have a high GI.
There are some considerations to keep in mind that may make using GI to control or prevent diabetes unreliable:
- The Academy of Nutrition and Dietetics mentions that GI of a food is based on eating that food with an empty stomach, without any other type of food. Very rarely do people eat like that.
- The GI of a food is based on 50 grams of carbohydrates for one serving and measuring the effect on the blood sugar. For example, a person would need to eat four cups of beets to one cup of rice to gain the same blood sugar level increase.
- Not every food has been calculated for GI. Existing data on foods studied is used to make a good estimate on other foods.
- Foods with a low GI are not always packed with nutrients.
- GI depends on how food is prepared. For example, instant oatmeal has a higher GI than steel-cut rolled oats.
Another measure called the glycemic load (GL) reflects the usual amounts of carbohydrate portions. This is calculated based on the GI and the portion size of the food eaten. As with the GI, the GL also has a scale of low or high. GL values less than 10 are considered low and greater than 20 are considered high. Glycemic load indicates the overall impact of the carbohydrate on the body based on the portion size eaten.
Aiming for both the type and the amount of carbohydrates consumed is a key to optimal blood glucose control, keeping in mind that not all carbohydrates are created equal. Research shows that using the GI and meal planning can improve diabetes control slightly, but can be complicated. Michigan State University Extension outlines the following factors affect the GI in foods:
- The more processed the food, the higher the GI.
- The riper a fruit is, the higher the GI.
- When carbohydrate foods are eaten as part of a meal, the average of the GI values is factored together. Therefore, you should pair a high-GI food with a low-GI food.
- Cooking time affects GI; longer cooking times may break down the starch more and allow it to pass through the body faster.
- Food acidity also affects GI. The more acidic a food, the lower the GI.
- Plant cell walls slow the digestive process, slowing carbohydrate breakdown.
- Adding protein or fat to a high GI food decreases the GI of that food.
- The higher the food is in soluble fiber, the lower the GI.
There is increasing evidence that choosing foods with low GI and GL shows a positive effect on blood glucose. It is very important to see your physician and/or diabetes educator to receive proper counseling to reach an optimal blood glucose level that works for you in the short term and long term. For more information on controlling your diabetes, visit MSU Extension's Diabetes website.