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The Glycemic Index - What You Need To Know

You may have heard the term glycemic index (GI) thrown around and wondered what it’s all about. Sounds complicated, right? Well, not really. 

At the most basic level, the glycemic index is a measure of how quickly a food causes our blood sugar levels to rise.

The measure ranks all types of food on a scale from zero to 100. Foods with a high glycemic index are more quickly digested and absorbed, causing your blood sugar to rise rapidly. Foods with a low glycemic index are digested and absorbed more slowly, allowing blood sugars to steadily increase, flatten out and slowly come back down.

In general, high GI foods tend to be (though not always the case) high in processed sugars and refined carbs (think doughnuts, french fries, soda, juice, white bread, white rice). Foods lower on the GI scale are often foods rich in fiber, protein and fat (think green veggies, most fruits, beans, lentils, nuts, oils, whole wheat breads and rice).

In general, the number is based on how much a food item raises blood glucose levels compared with how much pure glucose raises blood glucose. GI values are divided into three categories:

  • Low GI: 1 to 55
  • Medium GI: 56 to 69
  • High GI: 70 and higher

Seems simple enough, right? But what about portion size???

The GI value does not take into consideration the quantity you would eat of a specific food. To address this problem, researchers have developed the idea of glycemic load (GL), a numerical value that indicates the change in blood glucose levels when you eat a typical serving of the food. The GL scale goes from 1 to 20.

  • Low GL: 1 to 10
  • Medium GL: 11 to 19
  • High GL: 20 or more

 I know, I just threw a lot of information at you. I hear you, you are wondering how you can use this information to achieve your nutrition goals, am I right?

While the GI was first developed as a strategy for guiding food choices for people with diabetes, there is some research that suggests it may be a useful tool to identify foods that we should be choosing on a daily basis. In general, low and moderate GI foods do tend to be “healthier” overall and should be included in a well-balanced diet, inclusive of minimally-to-no processed foods, whole-grains, fruits and vegetables.

Those who follow a plant-based diet are likely already consuming high amounts of low and medium GI foods that are energy-packed and nutrient-dense. Go you!

 

I’m not forgetting about our high-performance athletes here either. Blood sugar levels can influence metabolic processes before, during and after exercise performance. Because of this, there has been a lot of research on using the GI as a tool in sports nutrition.

In short, we are finding that low GI foods high in carbohydrates are optimal for pre-competition fueling. High GI, high carbohydrate meals are optimal for post-exercise refueling when recovery time is short, and low GI foods may be beneficial for athletes trying to maintain low levels of body fat.

GI value does not provide us with any specific nutritional information about a given food item (vitamin and mineral content, fat content, etc.) and the GI value can be affected by several factors including how the food is prepared and/or processed, and what other foods are eaten at the same time. While I would not necessarily recommend using the GI as a hard-and-fast diet plan, it certainly can be included in your nutrition tool-box when deciding which foods to choose to fuel your hustle. Until next time…

Sources:

Academy of Nutrition and Dietetics. (2019, October). What is Glycemic Index? https://www.eatright.org/food/nutrition/dietary-guidelines-and-myplate/what-is-glycemic-index

 

O'Reilly J, Wong SH, Chen Y (2010) Glycaemic index, glycemic load and exercise performance. Sports Med. 40 (1), 27-39.

Ashley Russo

Ashley is an active registered dietitian nutritionist, healthy eating expert and wellness enthusiast. She graduated from Syracuse University, where she received a MA in Nutrition Science. In 2018, Ashley was named one of the Academy of Nutrition and Dietetics’ Recognized Young Dietitians of the Year. She currently works as a clinical dietitian at Update Medical University, where she specializes in nutrition support. As a former competitive figure skater, Ashley understands the connection between input and output, as it pertains to nutrition and performance.

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