What is the Glycemic Index?
~ July 2003 No.168 ~
For most people watching their fat intake is the most important part of their diet. But it may well be that the amount - and more importantly the type - of carbohydrate in the diet should be controlled.
Carbohydrates are nutrients that contain sugars. Some carbohydrates are simple. For example, sucrose (table sugar) contains the two sugars glucose and fructose. Other carbohydrates are more complex and may contain several different simple sugars or may contain large numbers of simple sugars bonded together.
Food carbohydrates are broken down in the intestinal tract by digestive enzymes and simple sugars, such as glucose, are then absorbed into the blood stream. The blood glucose stimulates the release of the hormone insulin which then starts the body's metabolism of the sugar.
The glycemic index of food is a ranking of foods based on their immediate effect on blood glucose (blood sugar) levels. A food's glycemic index refers to how much and how quickly that particular food raises blood sugar levels after consumption. Glycemic index is most useful when looking at foods high in carbohydrates (grains, breads, pasta, sweets), which are broken down directly into glucose and enter the bloodstream rapidly. Other nutrients such as proteins and fats have lower glycemic index values because they must be converted from amino acids and fatty acids (respectively) to glucose before they can increase blood glucose levels. In the laboratory, where glycemic index is measured, the after-meal blood glucose levels produced by a particular food are compared to a standard amount of pure glucose.
Many factors affect the glycemic index. Foods eaten alone have a different index than when eaten with other foods. For example, the glycemic index of rice differs greatly depending on the variety and the type of processing used. For fruits such as bananas, ripeness can have marked effects on glycemic index. The combination of different foods when consumed as well as a person's age, activity level and rate of digestion also can affect glycemic index.
|Wholemeal rye bread (30g):||68|
|Buckwheat pancake (77g):||102|
|White rice -boiled (150g):||45|
|Raw apple (120g):||40|
|Orange juice (264g):||46|
Glycemic index: overview of implications in health and disease
Am J Clin Nutr 2002,76:266S-273S