Does the Glycemic Index Work for Fat Loss?

The glycemic index is a measure of how fast or how slow, food increases your blood sugar. The higher the number, the faster your blood sugar increases in response to a given food; the lower the number, the slower your blood sugar increases. 

Here is a list of some common foods and their glycemic index (1): 

  • White bread: 75 
  • Barley: 28 
  • Apple: 36 
  • Ice Cream: 51 
  • Fructose: 15 
  • Glucose: 103 

Does the glycemic index work for fat loss?

The short answer here is it can, but it probably isn’t due solely to the glycemic index. Also, choosing a diet based on the glycemic index is not likely the best criterion when selecting a diet for weight loss. Let’s dive into the science and dissect this a bit.  

There have been studies that have shown that low glycemic index diets do result in fat loss (2). However, when they are compared head-to-head with other diets, they are not inherently more effective for weight loss (3, 4, 5, 6). 

So why would a diet that uses a low glycemic index work in the first place? That is a great question. Typically, low glycemic index diets follow strict caloric restriction parameters, which lead to weight loss. Alternatively, if they are prescribed ad libitum, low glycemic index diets tend to lead to lower calorie intake as they tend to be higher in vegetables, fruits, and sometimes protein, which causes spontaneous caloric restriction (7). 

The glycemic index is likely an obsolete tool.

The glycemic index was a useful tool for predicting a person’s glucose response to a specific food for almost 30 years. It was the backbone for many people with glucose issues (e.g., type 1 diabetes). However, recent evidence has suggested that it may be obsolete, and we may need to start thinking about the glycemic index much differently.  

A recent study took 800 individual people and measured the blood glucose levels in response to food and mapped each person’s unique response to a variety of foods (8). What they found was quite interesting. Instead of seeing very similar answers, they found very different responses to foods among people. For example, let’s say Alice and Bob both consume a banana, and a day later, they both consume a cookie. Alice might see a significant glycemic response to the banana while Bob has virtually no reaction to the banana; in fact, his blood glucose levels might drop. The next day we see that Alice has no glycemic response to the cookie, but Bob does. This is what occurred in this study. 

That fact leads us to a few key questions. Why do people respond differently, and does that mean anything for weight loss?

Let’s tackle the first question. Based on the research, Alice and Bob have very different responses to the same food due to their baseline insulin resistance, BMI, age, and, most importantly, their microbiome!

The second question is, does this information mean anything for weight loss? From what we can tell, the individualized glycemic response to carbohydrates is not likely to be a critical factor for weight loss. However, it may be necessary for managing some metabolic disorders, such as diabetes or metabolic syndrome.

How do I utilize the glycemic index in my coaching?

Recent scientific advances have shown us that the glycemic index is a relatively crude tool. However, that doesn’t mean it is entirely useless and that you can’t use it in your coaching.

The glycemic index is not going to be a significant focal point for weight loss for almost all of your clients. It will not serve as the foundation upon which you base your coaching. It can, however, help your clients with food selection.

For example, if you have a client who has glucose issues, educating them on foods that may cause more significant glycemic responses might help them manage their glucose better.

If you are working with an athlete who needs to use easily digestible, fast-acting carbohydrates, educating them on the glycemic index, providing a list of foods, and then allowing them to test some of the options can be very beneficial.

The Wrap Up

The glycemic index is an estimate of how fast your blood sugar increases in response to certain foods. Recent research has shown there is more of a difference between people’s glycemic index than previously thought, and the index is more of a starting point than it is dogma. Eating a low-glycemic diet can help with weight loss, but it is not any more helpful than other diets that assist with caloric restriction. Understanding the limitations of the glycemic index and how it might be used can help you decide whether or not to use it when coaching clients.

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The Author

Brad Dieter

Brad Dieter

Brad is a trained Exercise Physiologist, Molecular Biologist, and Biostatistician. He received his B.A. from Washington State University and a Masters of Science in Biomechanics at the University of Idaho, and completed his PhD at the University of Idaho. He completed his post-doctoral fellowship in translational science at Providence Medical Research Center, Providence Sacred Heart Medical Center and Children’s Hospital where he studied how metabolism and inflammation regulate molecular mechanisms disease and was involved in discovering novel therapeutics for diabetic complications. Currently, Dr. Dieter is the Chief Scientific Advisor at Outplay Inc and Harness Biotechnologies and is active in health technology and biotechnology. In addition, he is passionate about scientific outreach and educating the public through his role on Scientific Advisory Boards and regular writing on health, nutrition, and supplementation.


  1. Katelyn
    January 12, 2020 at 7:27 am — Reply

    This is all very interesting! I’d love to see the sources. I’m not seeing them. Can you please help me find them?
    Thanks in advance!!

    • National Academy of Sports Medicine
      January 13, 2020 at 10:44 am — Reply

      Hi Katelyn – thanks for reading this article! You can see the sources by clicking on the numbers in parentheses throughout the article. Please let us know if you have any other questions!

  2. Katrin Perchat
    January 13, 2020 at 8:51 am — Reply

    As Inunderstood through my studies of “introduction in the human microbiome” the microbiota of the intestines plays a key role in how food can be used or not. Taking this information, I suggest that a diverse and natural nutrition base is key for good functioning of our entire body. If someone gets a higher glycemic index with ingestion of a banana, it might be that the bugs for breaking the banana properly down and using its different nutrients are not amongst the microbiota. That is my guess.

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