The Glycemic Index: Should You Eat By the Numbers?

As a registered dietitian nutritionist (RDN), and a certified diabetes care and education specialist (CDCES), I get questions all the time from my clients about the glycemic index (GI)—especially from those working with me for weight loss, and/or to manage their diabetes.

The GI is a measurement of how fast a particular carbohydrate raises blood glucose—also called blood sugar. Some carbohydrates trigger a quick spike in blood sugar, while others work more slowly, keeping blood sugar more even. The GI addresses these differences by assigning a number to foods that reflects how quickly they increase blood sugar, as compared to pure glucose.

The GI goes from 0-to-100. Pure glucose has the highest GI and is given a value of 100. Foods with a high GI are thought to raise blood sugar quickly, while a lower GI food, which is absorbed more slowly, will raise your blood sugar more slowly.

Unfortunately, a person’s GI is more complicated than it might seem. Even foods with the same carbohydrate content can affect your blood sugar differently, depending upon the GI of the food. And, a food may have a different GI depending on how it’s prepared; so, you count the GI of a potato differently if you boil it than if you bake it. It is a lot to keep track of, which is why many nutrition professionals don’t use the GI at all when counseling patients or clients.

From our partner

Do you still have gout symptoms even though you're taking medication? You’re not alone. The Kadence study is a clinical research study for adults with uncontrolled gout. Learn More

A recent survey of more than 750 Today’s Dietitian readers, sponsored by Potatoes USA, found that 73% of nutrition professionals who responded don’t use the GI when counseling clients and patients, and among those who did report using it, 70% don’t use it often.

Moreover, researchers are concerned that people may think that foods with a low GI are healthier than foods with a high GI, and choose foods based only on the GI. In fact, 3 out of 5 nutrition professionals surveyed strongly agree that eliminating high GI foods from the diet and consuming only low-GI foods can cause people to exclude perfectly healthful foods from their diet. They also agree that the GI leads to misinformation about the healthfulness of fruits and vegetables. For example, potatoes, carrots, watermelon and ripe bananas have a GI categorized as “high,” and this GI might lead people to exclude them from their diets.

I counsel my clients about the general concept of fast and slow-acting carbohydrates, and help them to prioritize foods higher in fiber—as many low-GI foods are higher in fiber—rather than being concerned about the GI of a food itself.

The following tips are additional ways to manage blood sugar without focusing on the GI:

From our partner

People 16+ years old struggling with lupus: Find out if the PHOENYCS FLY Study may be for you. Study-related care provided at no cost.

• Look at the total nutrition of a food. Just because it is a high GI does not mean it doesn’t have other nutritional benefits, or just because it is a low GI does not mean that it is necessarily healthy
• Combine high GI foods with a protein or fat to lower the GI. For example, have a baked potato topped with low-fat chili
• Eat whole grains, because they tend to have a lower GI due to their fiber content.
• Instead of creamy dressings, consider those with vinegar: They will slow digestion as much as a high-fat dressing but without the added calories. Slowing digestion will lower the GI
• Eating cooked potatoes in foods such as potato salad lowers the GI. However, watch the mayonnaise or dressing you use to prepare the salad
• Portion size is just as important as GI because the more you eat, the higher your blood sugar will go regardless of the GI of the foods you’re consuming
• Check your blood sugars two hours after a meal to find out how your body deals with a food, or a meal.

Constance Brown-Riggs is a registered dietitian nutritionist, a certified diabetes care and education specialist, national speaker and author of the Diabetes Guide to Enjoying Foods of the World and the African American Guide to Living Well with Diabetes. She is also a paid partner of Potatoes USA. Follow her on social media @eatingsoulfully.