Clips on SugarNumber 9, 2002                 Glucose  Video Video

For Up-to-Date Information
on the various types of Sugars in Healthy Eating
...........................................................

This article was reviewed for accuracy by Thomas M.S. Wolever, MD, PhD, Professor, Department of Nutritional Sciences, Faculty of Medicine, University of Toronto and Clinical Nutrition and Risk Factor Modification Centre and the Division of Endocrinology and Metabolism, St. Michael’s Hospital, Toronto, Ontario.

Understanding the Glycemic Index

Printer-Friendly Version
PDF format

Carbohydrates in foods, including starches and sugars, are digested and converted into the sugar, glucose, by the body. Glucose enters the blood stream and circulates to all cells in the body providing energy for daily activities. The amount that a food is able to increase a person�s blood glucose (also called blood sugar) is called the glycemic response. The glycemic index (GI) was developed to rank foods based on their glycemic response. This is important because a lower GI diet may be helpful for people with diabetes and beneficial in preventing certain diseases.

Over 20 years ago, researchers at the University of Toronto studied more than 50 carbohydrate-rich foods and their effects on blood glucose. The GI was developed as a tool to measure how much a person�s blood glucose increases 2 to 3 hours after eating a carbohydrate-rich food compared to a reference food, which is either pure glucose or white bread. To date, there are over 750 published GI values of various foods.

A major determinant of the GI of a food is the rate of carbohydrate digestion, absorption and metabolism. A food that is easily broken down during digestion and quickly absorbed has a high GI value. The blood glucose response is fast and high. A food that is digested and absorbed slowly has a low GI value. Foods can be classified as having a low (< 55), intermediate (55 � 70), or high GI (> 70) with glucose as the reference standard. Some foods, such as legumes and milk products, tend to have low GI values while other foods vary from low to high within their food group.

Examples of GI values of foods within food groups*
  LOW INTERMEDIATE HIGH
Milk & Milk Products Skim Milk       32
Yogurt           33		  -  -
Fruits Apple            39 Banana            60 Watermelon   72
Root
Vegetables		 Sweet
Potato           54		 Baked Potato    60 Mashed
Potato           85
Legumes Red Beans     26
Chickpeas      33
Kidney Beans 39		  -  -
Grains Barley           25 Brown Rice       66 Instant Rice    87
Cereals All Bran™      51 Frosted
Flakes™          55		 Corn Flakes    81
Sweeteners Fructose       14 Sucrose
[table sugar]     60
Honey             67		 Glucose        100
*Compared to the reference standard of glucose (GI = 100).

 

 

Glycemic Index and Health

Research has shown that eating low GI foods may be beneficial for people with diabetes. The slow digestion and gradual rise and fall in blood glucose after a low GI meal helps control blood glucose. The use of low GI foods helps to prevent extreme blood glucose changes and the slow absorption of carbohydrates means the pancreas doesn't have to work as hard to make insulin.

The concept of GI helps to dispel myths related to sugars and diabetes. It was previously believed that sugars were harmful for people with diabetes because it was thought that they caused a rapid and greater increase in blood glucose than starchy foods, such as potatoes and breads. However, it was found that some sugars actually have a lower GI than many starchy foods. Sugars and sugary foods in moderate servings have no greater effect on blood glucose than many starchy foods and can be safely included as part of a diabetic meal plan. Many health organizations, including the Canadian Diabetes Association and the World Health Organization, support the use of GI for people with diabetes.

Scientists have also found that a low GI diet may help lower the risk of developing diabetes and heart disease in healthy individuals. The use of low GI has also been suggested for weight control. In contrast, a higher GI diet may be helpful for athletes to improve performance.

Factors affecting Glycemic Index

The blood glucose response to the intake of carbohydrates is not straightforward; GI values of a food can be influenced by many factors. Some food processing methods and nutrients can increase or decrease the GI value of a food.

Factors that
lower GI
Mechanism
Examples
Cooking or
processing starch		 When a food is highly processed or cooked, the structure of the starch changes and the granules become swollen (gelatinized). Less gelatinized starch is digested slower resulting in a lower GI. ‘Al dente’ pasta has a lower GI than
overcooked pasta
Sugar Sugar helps prevent the swelling (gelatinization) of starch granules Frosted Flakes™ has a lower GI than Corn Flakes
Fiber Soluble fibre slows down interaction between the starch and enzymes High fibre foods such as rolled oats, beans, lentils, apples, have low GIs
Protein and fat Slows down the rate of stomach emptying and carbohydrate digestion Foods that contain fat and protein, such as milk and legumes have
low GI
Acids in foods Slows down the rate of digestion and absorption Addition of Vinegar, lemon juice and
acidic fruits lower GI

 

What Should I Do?

Research shows that a low GI diet can be beneficial for all people, but remember, GI is only one component of a healthy diet. The basis of a low GI diet echoes the recommendations of Canada�s Food Guide to Healthy Eating � increase consumption of fruits, vegetables, whole-grains, breads and cereals, and legumes. These food groups are lower in fat, high in fibre, and rich in vitamins, minerals, and antioxidants. However, it is important to consume a variety of foods since some high GI foods contain essential nutrients and provide energy. For example, although mashed potato has a high GI, it is a nutritious food packed with vitamin C and potassium.
TIPS
  • Don�t choose foods based solely on their GI values � consider the overall nutrient value of the food.
  • Aim to achieve 1/3 to 1/2 of carbohydrate intake with lower GI foods.
  • Include at least one low GI food at a meal.
  • Include some protein and fat at each meal.
  • Combining a high GI food with a low GI food will give you an intermediate GI meal.

Want more information?

Visit the following Web sites:
www.diabetes.ca
www.glycemicindex.com
Speak to your health professional
or contact a Registered Dietitian.

...........................................................

This fact sheet, developed with the collaboration of Registered Dietitians,
is published by the Canadian Sugar Institute. If you have any questions
about sugars and their relation to nutrition and health, feel free to contact, either by email, fax or by mail:

CSI Nutrition Information Service    Canadian Sugar Institute
   c/o Nutrition Information Service
   10 Bay Street, Suite 620
   Toronto, Ontario M5J 2R8
   Fax: (416) 368-6426
  top of page  top of page
.......................................

CANADIAN SUGAR INSTITUTE
10 Bay Street, Suite 620 Toronto, Ontario M5J 2R8
Fax: (416) 368-6426   E-mail: info@sugar.ca
website: http://www.sugar.ca

 
Reliable health information - quality assured by the Victorian government. 
11 June, 2005
Contact usAbout usSubscribeLinks
Home > Topics > Common conditions > Diabetes > Management > Carbohydrates and the .... Need help? 
TopicsArrow
LibraryArrow
Healthy eatingArrow
Ask the expertsArrow
Service directoryArrow
NewsArrow
EventsArrow
Health toolsArrow
Health translationsArrow
gradient background image
 

Carbohydrates and the glycaemic index

  
  Food provides fuel for our body in the form of fat, protein, carbohydrates and alcohol but carbohydrates are the body's preferred fuel source. Carbohydrate-containing foods include bread, breakfast cereals, rice, pasta, legumes, corn, potato, fruit, milk, yoghurt, sugar, biscuits, cakes and lollies.

Digesting and absorbing carbohydrates
The digestive system breaks down carbohydrate-containing foods into simple sugars, mainly glucose. For example, both baked beans and soft drink will be broken down to simple sugars in your digestive system. This simple sugar is then carried to each cell via the bloodstream. The pancreas secretes a hormone called insulin, which helps the glucose to migrate from the blood into the cells. Once inside a cell, the glucose is 'burned' along with oxygen to produce energy.

The body converts any excess glucose from food into another form called glycogen. This is stored inside muscle tissue and the liver, ready to supplement blood sugar levels should they drop between meals or during physical activity.

The glycaemic index
Carbohydrate-containing foods are rated on a scale called the glycaemic index (GI). This scale ranks carbohydrate-containing foods based on their immediate effect on blood sugar levels. The GI compares carbohydrate-containing foods gram-for-gram of carbohydrate.

Carbohydrate-containing foods are compared with glucose, which is given a GI score of 100. Carbohydrates that break down quickly during digestion have the highest glycaemic indexes (GI more than 70). These high GI carbohydrates give a 'quick hit'. The blood glucose response is fast and high.

Carbohydrates that break down slowly release glucose gradually into the bloodstream. They have low glycaemic indexes (GI less than 55). The blood glucose response is slower and flatter.

Choosing between high and low GI foods
Which carbohydrate foods are best to eat? That depends on the situation. For example, the rate at which porridge and cornflakes are broken down to sugar is different. People with type 2 diabetes, or impaired glucose tolerance, cannot produce insulin rapidly enough to match the quick breakdown of cornflakes to simple sugars. This means their blood glucose levels may rise above the normal level. Porridge is digested to simple sugars much more slowly so the body has a chance to respond with production of insulin and so the rise in blood glucose levels is less. Porridge is a better choice of breakfast cereal than cornflakes for people with type 2 diabetes. It will also provide more sustained energy for other people as well.

How much you eat is also important
The amount of the carbohydrate-containing food eaten will also affect the blood glucose levels. For example, even though pasta has a low GI it is not advisable for people with diabetes or impaired glucose tolerance to have a large serve. This is because the total amount of carbohydrate, and therefore the kilojoules, will be too high.

GI and exercise
Eating low GI foods two hours before endurance events, such as long distance running, may improve exercise capacity. It is thought that the meal will have left your stomach before you start the event but remains in your small intestine releasing energy for a few hours afterwards. On the other hand, high GI foods are recommended during the first 24 hours of recovery after an event to rapidly replenish muscle fuel stores (glycogen).

High GI foods are influenced by low GI foods
Generally, eating low GI foods slows down the absorption of glucose from any high GI foods eaten at the same time. This is important, as most foods are eaten as part of a meal and this affects the GI value of foods. For example, eating cornflakes (a higher GI food) with milk (a lower GI food) will reduce the effect on blood sugar levels.

If a person with diabetes experiences a 'hypo', where the blood glucose levels fall below the normal range of 3.5-8mmol/L, then they need to eat foods with a high GI to restore the blood sugar levels to normal quickly. For example, eating five jellybeans will help to raise blood glucose levels quickly. This is silly there is no glucose in jelly beans. Quicker than what? The digestive system does not digest on demand it works at the same rate whatever you eat. Furthermore the digestion is automatic you cannot control it with the brain.

GI scale examples
Some examples of the GI rating of various carbohydrates include:
  • Low GI (less than 55) - soy products, beans, fruit, milk, grainy bread
  • Medium GI (55 to 70) - sugar, orange juice, oats
  • High GI (greater than 70) - potatoes, wholemeal and white bread, rice.

Factors that affect the GI of a food
Factors such as the size, texture, viscosity and ripeness of a food affect its GI. For instance, an unripe banana may have a GI of 30 while a ripe banana has a GI of 52. Both ripe and unripe bananas have a low GI.

Fat, protein, soluble fibre, fructose (a carbohydrate found in fruit) and lactose (the carbohydrate in milk) also generally lower a food's glycaemic response. Fat and acid foods (like vinegar, lemon juice or acidic fruit) slow the rate at which the stomach empties and so slow the rate of digestion, resulting in a lower GI. Other factors present in food, such as phytates in wholegrain breads and cereals, may also delay a food's absorption and thus lower the GI.

Cooking and processing can also affect the GI - food that is broken down into fine or smaller particles will be more easily absorbed and thus have a higher GI.

GI symbol on packaged foods
A food packaging symbol, G - Glycaemic index tested, for comparing the effect of different foods on blood sugar was launched in Australia in July 2002. The GI symbol indicates the GI rating of packaged food products in supermarkets. It ranks food products based on the speed at which they break down from carbohydrate to sugar in the bloodstream.

The GI symbol will only appear on food products that meet certain nutrient criteria for that food category. High and intermediate GI soft drinks, cordials, syrups, confectionery and sugars are excluded. Jams, honey and other carbohydrate-containing spreads are not necessarily excluded.

Using the GI as a guide to healthy eating
The GI can be used as a guide to healthy eating, as long as you are aware of the limitations. For example, the GI of some fruits, vegetables and cereals can be higher than foods that are considered to be treats, such as biscuits and cakes. This does not mean we should replace fruit, vegetables and cereals with treats, because the former are rich in nutrients and antioxidants and the latter are not.

It is not always possible or necessary to choose all low GI foods. There is room in a healthy diet for moderate to high GI foods and many of these foods can provide important sources of nutrients. If you mix a low GI food with a high GI food, you will get an intermediate GI for that meal.

Tips for healthy eating
Some practical suggestions include:

  • Use a breakfast cereal based on oats, barley and bran.
  • Use grainy breads or breads with soy.
  • Enjoy all types of fruit and vegetables.
  • Eat plenty of salad vegetables with vinaigrette dressing.
  • Eat a variety of carbohydrate-containing foods. If the main sources of carbohydrates in your diet are bread and potatoes then try lentils, legumes, pasta, basmati rice and pita breads.

Expert medical supervision
If you have a medical condition, such as diabetes, it is important to seek the advice of your doctor or specialist before making any changes to your diet.

Where to get help

  • Your doctor
  • Dietitian.

Things to remember

  • The glycaemic index (GI) rates carbohydrates according to how quickly they raise the glucose level of the blood.
  • The glycaemic load (GL) rates carbohydrates according to the glycaemic index and the amount of carbohydrate in the food.
  • A low GI rating of a food does not mean you can eat a larger serve of that food - the total amount of carbohydrate consumed is still important.
  • Choose a diet containing plenty of fruits, vegetables and legumes but with smaller helpings of potatoes and less highly refined grain products and concentrated sugar.
 Content partner 
More information 
Print a fact sheet 
Send me a copy 
Email this article 

 
  Related articles:
Carbohydrates explained.
Diabetes and healthy eating.
Diabetes explained.
Sporting performance and food.

This page has been produced in consultation with, and approved by:

Deakin University - Faculty of Health and Behavioural Sciences
(Logo links to further information)

Article publication date: 14/08/2000
Last reviewed: November 2004

Quality assurance
This article, like all articles on the Better Health Channel, has passed through a rigorous and exhaustive approval process. It is also regularly updated. For more information see our quality assurance page.

  
  Site map | Link to us | Copyright | Disclaimer | Privacy | Access tips | Accreditation