The glycaemic index is a measure of the ability of a food to raise blood sugar levels after it is eaten. When a person’s blood sugar rises, insulin is produced to counteract it. High levels of blood sugar and insulin can lead to problems like weight gain, insulin resistance, hypoglycaemia, and heart disease. Choosing foods that have lower glycaemic indices can help minimise or avoid these problems.

• Access the glycaemic index database to find out the value for specific foods (www.glycaemicindex.com).

• A value less than 55 indicates a low-glycaemic-index food.

• Talk to a doctor or a trained healthcare professional such as a registered dietitian if you want to use the glycaemic index as part of your overall eating plan.

Best bets: Whole grain breads and pasta, beans, and most vegetables and vegetable juices

More about this diet

The glycaemic index compares the blood sugar response to a particular food with the body’s reaction to pure glucose, which is given the value of 100. For example, if a food raises blood sugar only half as much as pure glucose, that food is given a glycaemic index of 50. The portion size used to test the glycaemic index of various foods is the amount that contains 50 grams of carbohydrate. Some research has used white bread instead of glucose as the standard of comparison for determining the glycaemic index of foods. The glycaemic index of a food is governed by a few factors, such as the form of carbohydrate it contains, the amount and form of fibre it contains, how much processing and cooking it has been subjected to, and the presence of other substances such as protein and fat.

Glycaemic load is a related measurement calculated by multiplying the glycaemic index of a food by the amount of carbohydrate contained in a typical serving of that food, and then dividing the result by 100. Glycaemic load may be more reliable than glycaemic index as a predictor of how a food will affect the blood sugar level. That is because some foods with a high glycaemic index (such as carrots) contain such a small amount of carbohydrate in a normal serving that they would not be expected to raise the blood sugar level very much. Carrot juice, on the other hand, which contains a relatively large amount of carbohydrate, would produce a substantial increase in the blood sugar level.