This buzzword has been around for a while now and is still gaining popularity - with good reason.

The glycaemic index, or GI, is an important tool for anyone who wants to control his or her blood-sugar levels. The list includes slimmers, diabetics, people with hypoglycaemia, and sportsmen and -women.

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What is the glycaemic index?
When we eat carbohydrate-rich foods, the carbohydrates are digested in the stomach and intestines and absorbed into the bloodstream in the form of glucose. The glucose in the blood stimulates the pancreas to excrete a hormone, called insulin, into the blood.

Insulin helps the body cells to take up glucose from the blood. Body cells use glucose as a source of energy. So, eating is followed by an increase in the levels of glucose and insulin in the blood. These increases in blood-glucose and insulin levels in the blood can be illustrated by drawing so-called blood-glucose and insulin graphs.

Several years ago, researchers discovered that carbohydrate foods don't all have the same effect on blood-glucose and insulin levels. For example, it was found that if a healthy person eats 50g of carbohydrate in the form of white bread, the increase in blood-glucose and insulin levels is greater than when the person eats 50g of carbohydrate in the form of spaghetti. To explain this difference, scientists coined the term "glycaemic index", or GI.

Definition of the glycaemic index
The GI of a food is defined as the size of the area under the blood-glucose graph after eating a portion of the food that will supply 50g of carbohydrate, divided by the size of the area under the blood-glucose graph caused by eating 50g of glucose.

This rather difficult concept becomes easier to understand if we try and imagine two graphs. After eating 50g of glucose, the graph, which illustrates the increase in the blood-glucose level is about 50 percent larger than the graph that shows the increase caused by eating 50g of carbohydrate from spaghetti. In other words, we can say that the GI of glucose is 100 and the GI of spaghetti is 50.

Researchers have classified many foods according to their GI. Carbohydrate-rich foods can now be classified into three broad categories, namely high-GI, intermediate-GI and low-GI foods.

Why is the glycaemic index important?
The GI is very useful in compiling diets for people who experience problems with glucose and insulin metabolism, such as diabetics, people who are overweight, and those who have high blood pressure, hypoglycaemia and/or high blood-fat levels.

By eating foods with a low GI, which will release glucose slowly and steadily into the blood and which will not overly stimulate insulin secretion, diabetes, insulin resistance, obesity and heart disease can either be prevented or controlled.

Use of the GI for sportsmen and women
On the other hand, GI values are being used to design diets for sportsmen and -women who require steady blood-glucose levels to sustain physical activity for long periods. Sports nutritionists increasingly rely on the use of the GI to develop diets that will prevent fatigue and increase endurance of athletes.

- (Dr I.V. van Heerden, DietDoc, updated October 2008)

Any questions? Ask DietDoc

 

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