The Glycemic Index: How Carbohydrates Affect You

By Perrin Braun, August 1, 2022

glycemic indexAs explained in our previous blog post, sugar is a carbohydrate used by your body for fuel. In this article, we’ll discuss the glycemic index, a method of distinguishing between different types of carbohydrates by measuring their effect on blood sugar, or glucose.


Blood DNA Fitness tracking ebookWhat is the glycemic index?     

To review, the blood sugar (also known as glucose) that is delivered throughout our bodies derives in part from the carbohydrates that we consume. The Glycemic Index (GI) measures how quickly carbohydrates in a food cause blood sugar levels to rise after eating and how quickly the carbohydrates convert to glucose in your body. The GI system compares all foods to pure glucose (or white bread), which causes a rapid spike in blood glucose levels and has a Glycemic Index value of 100. High-glycemic foods digest and absorb into the bloodstream quickly, which causes large, rapid changes in blood sugar levels.  Low-glycemic foods digest and absorb more slowly, which produces gradual rises in blood sugar and insulin levels.  To find out your blood sugar levels, sign up for one of the InsideTracker plans. You’ll learn your fasting glucose measurement and receive recommendations for lifestyle, exercise and diet changes that will help you improve your glucose levels.


What is the role of sugar in the body?

After we eat foods that are high in carbohydrates, our digestive system breaks them down and turns them into glucose, which enters the bloodstream. From there, the glucose enters individuals cells throughout the body and provides them with the energy that they need to function. Any glucose not immediately needed by the cells is stored in your liver and muscles for future use. Two important hormones help regulate the level of sugar in your blood: insulin and glucagon. When your blood sugar level is high, insulin moves the sugar from your blood into your cells. In contrast, glucagon works to release the sugar that is stored in your liver when your blood sugar levels are low. This process helps to ensure that your body maintains a steady, natural balance in your blood sugar.

Click here to learn how InsideTracker can recommend carbohydrates that fit your unique taste preferences and physical needs!

Here’s where the glycemic index comes in: it ranks foods and beverages containing carbohydrates based on how they affect your blood sugar levels. The scale ranges from 1-100, but only foods that contain carbohydrates appear on the scale since they have the most significant effect on blood sugar levels. Here’s the breakdown: 


High glycemic foods  Scores between 70-100 White rice, white bread, watermelon, skinless backed white potatoes
Medium glycemic index Scores between 56-69 Sweet potatoes, raisins, bananas, raw pineapple, sweet corn
Low glycemic index Scores between 0-55 Raw carrots, peanuts, raw apples, grapefruit, peas, skim milk, lentils, most vegetables, and kidney beans


The GI Diet 

Some people claim that following a diet based on low GI foods can help you lose weight and help keep blood sugar levels more stable. Advocates of this plan say that your body quickly digests high GI foods, leading to rapid fluctuations in blood sugar. Conversely, foods that are low on the GI scale are digested more slowly, and thus raise blood sugar in a more controlled and regulated way. Because these foods stay in your digestive tract longer, you are likely to feel full for longer. However, studies suggest that low-GI diets may be helpful for some people, but should be part of an overall strategy of eating healthy foods, maintaining optimal weight, and getting enough exercise.

If you are an athlete, understanding GI can help you improve your performance and recover more quickly following exercise. After strenuous workouts or events, healthy higher glycemic foods can help to quickly refuel the body’s glycogen stores and to provide the energy necessary for muscle repair. Some studies suggest that athletes should eat moderate- to high-glycemic foods during endurance events to maximize all of their carbohydrates for optimal performance. 


How do I find the GI score for a food?

There are many online lists of the Glycemic Index scores of various foods. But many foods have not been evaluated. Here are some tips that can help you estimate a food’s GI:

Color: Foods that are white tend to have a higher GI. Not only does this include processed foods made from white flour and white sugar, but foods like white potatoes also have a high GI. But be aware that many darker foods also have high GI scores.

Fiber: Foods that are high in fiber generally take longer to digest, and therefore cause your blood glucose levels to rise more slowly than low-fiber foods. High-fiber foods include whole grains, legumes, nuts, seeds, and fruits that are eaten with their skin intact.

Protein: High-protein foods are typically low on the GI scale. Foods like legumes are rich in both fiber and protein, and are a healthy choice for any diet. Other low-GI protein foods include nuts, seeds, fish, and lean meats.

High Fiber Foods

What doesn’t the GI scale tell you?

Because the GI scale ranks foods based on how they affect blood sugar levels, it doesn’t take into account their actual nutritional value. Some low-GI foods may be less healthy than high GI foods because they may contain more calories or saturated fat.  For instance, potato chips and ice cream have lower GI scores than baked potatoes, even though baked potatoes are generally a healthier choice. If you just pay attention to GI values, you might eat too many calories.  Some low-GI foods such as peanuts are high in calories and should be consumed in small amounts. 

Additionally, the rate at which your body processes carbs can vary based on how much you eat, the ripeness of the food, what time of day it is consumed, how it is processed, and other foods that you may eat it with. The effective GI value can also change based on how you prepare the food and what else you eat with that particular food. Applesauce has a higher GI and a greater effect on your blood sugar than a raw apple. Your body digests proteins and fats more slowly than carbohydrates. Eating proteins and fats at the same time as carbohydrates slows digestion and reduces the effect of the carbohydrate on blood sugar. If you spread a tablespoon of peanut butter on your toast, you can add protein to your breakfast and lower the effective GI of your meal. 

While the glycemic index tells you how rapidly a carbohydrate is converted into glucose, the glycemic load (GL) takes into account the amount of carbohydrate in a typical serving size. Watermelon, for example, has a high glycemic index, but a serving of watermelon is mostly water with a small amount of carbohydrates. The GL of watermelon is therefore relatively low.

Instead of eating a strict low-glycemic diet, the best strategy is to eat a variety of foods, including vegetables, fruits, healthy fats, and lean protein. Choose healthy carbohydrates, such as whole grains, legumes, vegetables, and fruits. And, if you are an athlete, consider adding higher glycemic foods to fuel your performance during events Remember that InsideTracker shows you which nutrients your body needs and can recommend the healthy foods that provide them!


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