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Healtheuniversity > English > Diabetes College > Eat Healthy > Fibre > What is the Glycemic Index (GI)?

What is the Glycemic Index (GI)?

The glycemic index (GI) is used to see how quickly the carbohydrates in these foods raise your blood sugar after eating them compared to a standard food (glucose or white bread).

Eat foods that have lower GI to help you:

  • manage your blood sugar better
  • lower LDL (bad) cholesterol and triglycerides (a type of fat in your blood)
  • lower your risk of getting heart disease
  • feel full longer, after eating

The glycemic index (GI) ranks carbohydrate foods using a scale from 0 to 100. This scale is used to see how quickly the carbohydrates in these foods raise your blood sugar after eating them compared to a standard food (glucose or white bread).

  • Foods with a high GI digest and absorb quickly into your body and can cause a rise in your blood sugar after eating. Limit the amount of food you eat that has a high GI number.
  • Foods with a low GI digest and absorb more slowly. These foods take a longer time to raise your blood sugar and cause a lower rise.

Often, foods with more fibre have a low GI. Eat foods with a low to medium GI instead of foods with a high GI.

The glycemic index does not rank foods based on nutrient content. This means that some foods may have a low GI, but may not be high in nutrition. It is best to eat foods with a low GI and that are high in nutrients.

How Can Low GI Foods Help Me Manage My Diabetes?

Research shows that eating foods that have lower GI can help you:

  • manage your blood sugar better
  • lower LDL (bad) cholesterol and triglycerides (a type of fat in your blood)
  • lower your risk of getting heart disease
  • feel full longer, after eating

What Other Factors Affect the GI of Foods?

There are 4 main factors that impact the GI of foods.

1. Food preparation

The more processed food is, the higher the GI. 

Processed foods have a high GI because much of the nutrients and fibre have been removed or broken. This makes the nutrients and fibre digest quickly and absorb in your body.

Processed foods with a high GI include:

  • instant noodles
  • instant rice
  • instant mashed potatoes
  • white bread
  • soda crackers
  • French fries
  • baking potatoes

These foods are high in GI and are not high in nutrients. Eat whole, fresh foods instead of processed foods. 

  • Choose steel cut oats instead of instant oatmeal.
  • Choose long-grain rice, such as basmati or brown rice, instead of instant short-grain or sticky rice.
  • Choose sweet potatoes or yams instead of instant mashed potatoes.
  • Choose to eat legumes (such as kidney beans, lentils, split peas and chickpeas) more often.
  • Choose fresh or frozen fruit instead of fruit juice. Juice is the processed form of fruit and will quickly raise your blood sugar.

2. Cooking time

The longer you cook food raises the GI. Overcooking food also raises the GI.

  • For example, cook pasta al dente. Al dente refers to pasta cooked only to the point that it is still firm when eaten.

Soft or overcooked pasta will have a higher glycemic index. This means that you should avoid overcooking foods.

3. Fat and protein

Adding fat and protein helps to lower the GI.

  • For example, Russet potatoes have a high GI. Adding some olive oil, non-hydrogenated margarine or plain Greek yogurt to a baked potato can lower the GI.

If you eat foods that are high in GI, add fat and protein to them.

4. Portions

The amount you eat can affect your blood sugar even if the food has a low GI.

  • For example, eating a large portion of a low GI food such as pasta can still result in a high blood sugar reading.

Keep your portions small.

Safety Tip

Check your blood sugar 2 hours after you start eating a meal. This can help you understand how the GI of foods affects your blood sugar.

Last Reviewed: 10/16/2016