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The Glycemic Index Days Are Gone!

Nina Ghamrawi, MS, RD, CDE
June 20, 2023
June 20, 2023

The glycemic index (GI) is a system that ranks how carbohydrate-containing foods affect blood glucose levels on a scale of one to 100. This system, now over 40 years old, has become controversial, and new evidence has proved it to be false. The index ignores many factors that determine how quickly carbohydrates are digested and absorbed. Here’s why we should retire it.

The Problems with Glycemic Index:

In fact, based on more recent research, carbohydrates can affect glucose differently depending on several factors about the food and meal:

  • How foods are grown, manufactured, cooked and stored
  • food serving size
  • the combination of foods eaten as part of a meal, like carbs with protein, or carbs with fat

The GI also has strange and complicated scores for many foods. Based on the lab, variety, cooking method, serving temperature, and other factors, the GI can be surprising.  For example:  

  • A candy bar has a better score than a slice of whole-grain bread
  • Rice, like many foods, has 126 different entries for various brands, regional varieties, and cooking methods. The GI scores range from 37 to 116.
  • The score differs depending on the lab that tests it. When seven different labs tested the same type of rice, GI scores ranged from 55 to 87
  • The GI tests carbohydrates by themselves, which are rarely actually eaten alone. Usually carbohydrates are paired with fat, protein and fiber, which change glucose absorption. Put cream cheese on the bagel, and the glycemic index drops

Glycemic Load: New Name, Same Problem

Attempts have been made to improve the index to better reflect real life. A calculation called “glycemic Load (GL) was added to reflect portion sizes. But its confusing. High-Index foods may have a low GL. For example, watermelon has a GI of 72, but the GL of a standard portion is only 4. It still suffers from the same issues as the index, but GL is just more complicated.

It’s Not One Size Fits All

The GI also doesn’t account for huge genetic, hormonal, and digestive differences in blood-glucose responses from different people. Due to dietary habits, physical activity, body composition and gut microbiome, even if you and 10 other people eat the same food, there can be a drastic difference in glucose response.  One study found significant glucose variability, even between identical twins.

In fact, age, stress, health status, baseline insulin levels, alcohol consumption and sleep also affect glucose response. Even the same person can have different responses to the same food eaten on consecutive days or at different times of the day.

So What Can We Do To Replace Glycemic Index?

There is no standardized, consistent and easy way to determine how a food is going to affect a person’s glucose. Everyone is unique. Therefore, solutions to glucose spikes and dietary guidance should always be individualized, and based upon a person’s unique response to a carb-containing food. Therefore, testing is ALWAYS most important to understand how your body reacts to food uniquely. If you don’t know, or you are eating a meal that is:

  • prepared a different way
  • Consumed after exercise
  • contains more  or less fat or protein
  • eaten with more snacks, or more alcohol in or before the meal
  • cooled down after cooking
  • hasn’t been eaten or tested against your glucose in a while

Then ALWAYS test before and 2 hours after the meal to see how your body may react differently.