Understanding the Glycemic Index

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What is the Glycemic Index?

The Glycemic Index (GI) is a scale from 0 to 100 that ranks a food or drink that contains carbohydrate by how much it raises your blood glucose (sugar) levels after it is consumed.  

Using the GI to help choose foods is one way to help manage blood glucose levels.  Diabetes Canada recommends people with type 1, type 2, or pre-diabetes choose lower GI foods and drinks more often to help control blood sugar.

Some foods that contain carbohydrate are digested quickly and therefore can raise your blood sugar level higher and faster, compared to other carbohydrate-containing foods that are digested slower and therefore do not raise your blood sugar as high or as fast.

The GI scale is developed by comparing each food to the reference standard food which is white bread or pure glucose which are given the highest possible score of 100.  They have been given this highest possible ranking on the GI scale because they raise blood sugar levels higher and faster than other foods.

Three GI categories have been developed:

  • Low GI (55 or less) 
  • Medium GI (56-69)
  • High GI (70 or more)

Diabetes Canada recommends eating foods in the low GI category most often, the medium category less often, and eat foods in the high GI category the least often. 

What are the benefits of eating low glycemic index foods?

There are many benefits of consuming a low GI dietary pattern, such as:

  • Low GI foods are digested slowly and therefore raise your blood glucose slowly which can help manage and control your blood glucose levels
  • Low GI foods tend to be higher in fibre which can help you feel full for longer and therefore can help with weight management
  • Research shows consuming mainly high GI foods can increase your risk of type 2 diabetes, while consuming more low GI foods can decrease your risk of type 2 diabetes and its complications
  • Research shows that high-fibre, low GI diets can reduce total and LDL (bad) cholesterol levels which is important to help decrease your risk of heart disease

What is the GI of some common foods?

Low GI (55 or less)Medium GI (56-69)High GI (70 or more)
Banana (green, unripe)Banana (ripe, yellow)Banana (brown, overripe)
PeachCranberries (dried) 
Sweet potatoPotato (red, white, cooled)Potato (instant mashed; red, white, hot)
Winter squashParsnip 
Breads, Cereals, Grains
Heavy mixed grain, spelt, sourdough bread, tortilla (whole grain)Pumpernickel, rye, whole wheat bread, pita, rotiWhite bread, naan
All bran type cereal Bran flake type cereal, Corn Flakes™, Puffed wheat, Rice Krispies™, Special K™  
 Cream of Wheat™ (regular)Cream of Wheat™ (instant)
Oats (steel cut)Oats (instant, large flake, and quick) 
Rice (parboiled, converted)Basmati, brown, short or long grain white, and wild riceJasmine, sticky, or instant white rice
Pasta (al dente, firm)  
PopcornStoned Wheat Thins™ crackersRice cakes, pretzels, soda crackers
Beans, Legumes
Baked beans  
Romano beans; lentils, soybeans/edamame, split peas  
Milk & Milk Alternatives
Milk (almond; cow – skim, 1%, 2%, whole; soy) Rice milk
Yogurt (skim, 1%, 2%, whole; Frozen)    

Looking to find the GI of other foods check here: The University of Sydney’s Glycemic Index Website

Some important points to highlight and understand:

  • Processing methods can impact the GI of foods.  In general, more processed foods tend to have a higher GI than less processed foods.  For example, instant oats which are more processed have a higher GI, compared to less processed steel cut oats which have a low GI.  Try to choose less processed foods more often.
  • How foods are prepared and cooking methods can impact the GI of foods.  For example, most pastas are usually low or medium GI, unless they are overcooked.  So, eat pasta cooked al dente (firmer).  Check your pasta package for cooking instructions.
  • The ripeness of a food impacts its GI.  For example, an overripe brown banana has a high GI, whereas a green banana has a low GI.
  • Combining foods will also change their GI.  Consuming low GI foods with high GI foods can help keep your blood sugar from rising quickly.
  • Each person can respond to the glycemic content of foods differently and the only way to know for sure how you respond is by checking your blood sugar before and after you eat that food.

Understanding the GI to help choose foods is just one aspect of healthy eating and one way to help manage blood glucose levels.

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