What is the GLYCEMIC INDEX? Why is it important to diabetics?

The Glycaemic Index (GI) is a ranking of foods based on their overall effect on blood glucose levels. Slowly absorbed foods have a low GI rating, whilst foods that are more quickly absorbed will have a higher rating. This is important because choosing slowly absorbed carbohydrates can help even out blood glucose levels when you have diabetes.

Foods are given a GI number according to their effect on blood glucose levels. Glucose or white bread is used as the standard reference (GI 100), and other foods are measured against this. The effect on blood glucose levels of a portion of the test food containing 50g of carbohydrate is compared with the effect of the reference food (white bread or glucose) over a three hour period. It was previously thought that if you ate the same amount of carbohydrate, then whatever that carbohydrate was, it would have the same effect on your blood glucose levels. It is now known that different carbohydrate-containing foods have different effects on blood glucose levels. For instance, 30g of bread does not have the same effect as 30g of fruit or pasta.

Yes I think that the GI index is useful and you will have heard of the GI diet? Because meals including low GI foods allow you to absorb carbohydrate more slowly, they help to maintain even blood glucose levels between meals and can therefore help you avoid ‘hypos’. The effect of a low GI meal can run into the following meal, which helps keep blood glucose more even during the whole day.

Slow acting carbohydrates will also reduce the peaks in blood glucose that often follow a meal, and this may have a role in helping to prevent or reduce the risk of getting Type 2 diabetes in those at risk. There are also benefits for weight loss. Low GI foods can help you to control your appetite by making you feel fuller for longer, with the result that you eat less. Research has shown that people who have an overall low GI diet have a lower incidence of heart disease.

Lower GI diets have also been associated with improved levels of ‘good’ cholesterol. One or two small changes can make all the difference.

Determining the GI of a meal is not so easy as reading a number off a chart. The addition of fat and protein slows down the absorption of carbohydrate. Chocolate has a medium GI because of its fat content therefore, and crisps and chips will actually have a lower GI than potatoes cooked without fat. Milk and other dairy products have a low GI because of their high protein content, and the fact they contain fat. The consequence of this is that if people were to confine themselves to low GI foods, their diet would be unbalanced and high in fat, which could lead to weight gain and increase their risk of heart disease. For this reason it is important not to focus exclusively on GI and to think as well about the overall balance of the diet.

Cooking method (frying, boiling and baking), processing, the ripeness of a fruit and the variety of a vegetable will also all affect a food’s GI rating.