What is the Glycemic Index?

examples of low vs high GI foods

Many of us have heard the terms “low GI food” or “high GI food” but what exactly is GI and why is it important?  The Glycemic Index (GI) is a measure of how carbohydrate foods affect blood glucose levels.

What is the Glycemic Index and why is it important?

Carbohydrate foods are digested by the body to make glucose, which is the “sugar” carried by the blood.  Eating carbohydrate foods causes blood glucose level to rise but some carbohydrates are digested quickly, whereas others are more slowly. The Glycemic Index (GI) is a scale that ranks carbohydrate-rich foods by how much they raise blood glucose (sugar) levels compared to a standard food. The difference between a high GI food and a low GI food can be important for your health.  Research suggests we can use the GI to make healthy food choices.

So how does GI work?

Carbohydrates (in grains, fruit, milk and sugars) are digested by the body and cause blood glucose to rise. The GI of a carbohydrate food was determined by having volunteers eat a certain amount of the carbohydrate containing food in question then having their blood glucose tested over several hours. The effect of this food on blood glucose is compared to the effect when eating a “standard” carbohydrate, which is known (in this case either  or a specific amount of pure glucose or white bread). Foods were then divided into three categories (low, medium and high) depending upon how they compared to the “standard” pure glucose or white bread.

Low and medium GI foods raise blood glucose more slowly and high GI foods raise blood glucose quickly.

Health benefits of lower GI foods

The GI has been studied for three decades and has revealed some very interesting facts about food. For example, many processed foods have a high GI and research seems to indicate that high GI foods may contribute to health problems. On the other hand, lower GI foods may prevent or help manage disease. Although not all scientists agree, many feel that lower GI foods may;

  • help manage diabetes by raising blood glucose more slowly after eating
  • help with weight control by keeping you full longer
  • lower blood cholesterol levels and reduce the risk of heart disease
  • reduce the risk of Type 2 diabetes.

 What is the GI of some common foods?

The GI applies to carbohydrate foods as these are the foods that digested into glucose.  Carbohydrate containing foods are not just breads and pasta and rice and other grains, but include fruit and milk products, as well. Most vegetables, protein foods (meat, fish, poultry, cheese) and fats are low in carbohydrate and have a low GI or no GI value.

Low GI

Medium GI

High GI

sweet potatoes and yams new potatoes Russet potatoes
converted (parboiled) rice brown rice, basmati rice white rice
breads made from heavy mixed grains, pumpernickel or stone-ground flours rye bread, whole wheat bread white bread
oat bran or All Bran™ cereal puffed wheat corn flakes, Rice Krispies™
slow cooking or steel cut oats quick oats instant oats


popcorn, rye crisp crackers pretzels, soda crackers

 (Chart adapted with permission from The Glycemic Index, Canadian Diabetes Association, 2006)

Tips for lowering the GI of your meals

  • You can lower the GI of a meal by replacing high GI foods with low and medium choices.
  • Balance your meals by adding protein and healthy fats to your carbohydrates. This will add nutrition and reduce the GI of your meal.
  • Use meatless protein such as legumes (lentils, chick peas, kidney beans and navy beans) for a low GI, high fibre, low fat choice.
  • Pastas are generally low or medium GI, but they can be high GI if overcooked or instant (such as ‘bowl noodles’). Eating pastas cooked “al dente” (or ‘to the tooth’ firmness) will result in it being lower GI.  For extra nutrition, try whole grain types
  • Choose low and medium GI foods more often

The GI and diabetes

People with Diabetes may find they can improve their blood glucose control by using lower GI foods more often. If you have Diabetes, try checking your blood glucose 2 hours after low and high GI meals (try to keep the portions of carbohydrate similar) to see if there is any difference.

Do note, however, that pure glucose is the best treatment for low blood glucose (hypoglycemia)  because it raises your blood glucose very fast! If you take medication to lower your blood glucose, always keep glucose tablets nearby.


The GI is another tool to enable us to make healthy choices. Whole grains, legumes, milk and dairy products, fruit and vegetables are all sources of carbohydrates, and therefore affect our blood sugar levels, however they also provide fiber, vitamins, minerals and great taste. So choose low GI foods more often and enjoy!


Foster-Powell K, Holt SHA, Brand-Miller JC. International table of glycemic index and glycemic load values Am J Clin Nutr. 2002;76:5-56

The Glycemic Index, Canadian Diabetes Association, 2006

 Barbara J. Allan - DC profile pic 105 x 124 pxThis article was written Barbara J. Allan, MHA, CDE, RD — Nutrition to You’s Diabetes Expert.  Click the buttons below to share it with a friend. To learn about Barbara and the services she provides, please click here http://www.nutritiontoyou.com/about-us/