Understanding the Glycemic Index

Ever wonder why some foods impact your blood sugar levels differently than others? You’re not alone!  Understanding how different foods have an impact on your blood sugar numbers doesn’t have to be rocket science. All it calls for is a little in-depth investigation.

Do you ever wonder why strawberries may not significantly impact your blood sugar numbers, while potatoes do? The answer can be found in the glycemic index. The glycemic index (GI) measures specifically how foods containing carbohydrates impact blood sugar numbers after eating (1). In other words, fruits, starchy vegetables, dairy products, beans, and legumes (all of which are carbohydrates) have unique GIs that impact how quickly or slowly blood sugar levels spike.

The GI rates the carbohydrates in foods on a scale of 1 to 100. The lower the GI number, the slower it raises blood sugar levels. Conversely, the higher the GI number, the faster it raises blood sugar levels. Remember those strawberries and potatoes from earlier? On the GI chart the strawberry has a value of 40, while the potato has a value of 85. We can see from this example exactly why potatoes may spike someone’s blood sugar numbers; potatoes have a higher GI rating than strawberries do. But potatoes and strawberries are not the only foods we eat that contain carbohydrates. To help you better understand how the foods you’re consuming impact your blood sugar numbers, let’s look a little further.

The GI can be broken up into three distinct categories: low, intermediate (also known as moderate) and high (2). Low GI foods have values of 55 or less; moderate GI foods have values in between 55-70; and high GI foods have values of 70 or higher. Carbohydrate-containing foods that have a low GI include strawberries, peanuts, skim milk, carrots, and kidney beans. A few common household foods that have a moderate GI include sweet potatoes, pineapple, and couscous. And foods that have a high GI include bananas, potatoes, honey, white bread, and refined grains.

There are many factors that can impact the glycemic index value. Some of these factors include dietary fiber, fat, protein, and how these work together with carbohydrates. For example, fiber, specifically fiber that is found in non-starchy vegetables, like lettuce, spinach, cucumbers and onions; fat that is found in cooking oils and butter; and protein that is found in fish, eggs and lean meats are considered to be carbohydrate-free foods and are not found on the GI. In other words, these foods by themselves cannot cause blood sugar spikes. Research suggests that fiber, fat, and protein may actually help in blood sugar management (2).

Remember that potato (glycemic index value of 85) we talked about earlier? Would you believe me if I told you that you could lower the GI of this food? It’s true! If you were to eat that same potato with a side salad (which contains fiber) and a serving of buttery lemon-pepper salmon (fat and protein), then the overall GI of that meal can be lowered. In other words, when a high GI food is combined with a fat, fiber and/or protein, the post-meal blood sugar levels will be lower than when that same GI food is eaten without the addition of that fat, fiber, or protein.

While all of this is true, not all carbs are created equally. The kind of carbohydrate that you choose to put into your meal makes a big difference. Know this: your body needs carbohydrates on a daily basis. So whenever you’re choosing a carbohydrate, the best practice is to pick one that is considered to be a whole grain (which has more fiber). Then you should pair it with a healthy fat and a lean protein. This is how you can successfully turn a food that has a high GI into a food that has a moderate or even a low GI food. Making these changes to create and eat complete, well-rounded meals can be a big help in better managing blood sugar levels!



(1) https://academic.oup.com/ajcn/article/110/4/891/5543221

(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4994556/

Published: December 31, 2020

Kim Rose is a Florida based registered dietitian nutritionist who specializes in health and wellness concerns for persons with diabetes. Her inclusive approach and philosophy revolve around “making nutrition easy and attainable”. Kim does this by addressing common and complex food and wellness topics for the general public and health professionals alike on her YouTube channel and contributing to multiple media outlets including Healthline, Huffpost, and Health Magazine just to name a few. Kim has close to a decade of professional experience and dedicates her time working at the hospital and counseling clients in her private practice. In her spare time Kim likes to run, podcast, and enjoy a large bowl of kettle corn.