WHAT IS THE GLYCEMIC INDEX AND THE GLYCEMIC LOAD?

Professor Jennie Brand Miller and her colleagues say…

The glycemic index (GI) is a physiologically based measure of carbohydrate quality – a comparison of carbohydrates (gram for gram) based on their immediate effect on blood glucose levels.

• Carbohydrates that break down quickly during digestion have high GI values. Their blood glucose response is fast and high.
• Carbohydrates which break down slowly, releasing glucose gradually into the blood stream, have a low GI.

The GI is simply a measure of carbohydrate quality – the extent to which the carbohydrates in different foods will raise blood glucose levels. A knowledge and appreciation of the GI will help you choose the right amount of carbohydrate and the right sort of carbohydrate for your health and wellbeing. Once thought to be of relevance only to people with diabetes, the GI is now considered a useful way for everybody to optimize health.

Most people have some notion of how blood ‘sugars’ ( in truth, glucose) rise and fall throughout the day. However, much of the information currently in print about food and blood glucose is wrong. THE NEW GLUCOSE REVOLUTION tells you the true story about the connection between carbohydrate and blood glucose.

• The blood glucose response to a meal is primarily determined by its carbohydrate content.
• Both the quantity and the quality of carbohydrate in the food influence the rise in blood glucose.
• Meals containing the same amount of carbohydrate can produce either high or low effects on blood glucose, depending on the type (or quality) of carbohydrate. In other words, It’s GI.

ON THE GLYCEMIC LOAD

Professor Jennie Brand Miller and her colleagues say…

“When we eat a meal containing carbohydrate, the blood glucose rises and falls. The extent to which it rises and remains high is critically important to health and depends on two things: the amount of carbohydrate in the meal and the nature (GI) of that carbohydrate. Both are equally important determinants of changes in blood glucose levels. Unfortunately, the amount of carbohydrate still gets the lion’s share of the attention.

It’s easy to determine the amount of carbohydrate in a food by looking at the food label or consulting food composition tables. What you can’t yet determine from the food label or the food composition is the GI of the carbohydrate. ( The New Glucose Revolution, 3rd edition, by Professor Jennie Brand Miller et al contains the GI of nearly 600 individual foods. It’s the largest, most comprehensive and reliable list of GI values in the world).

Because both the amount and type of carbohydrate are needed to predict blood glucose responses to a meal, we need a way to combine and describe the two. Researchers at Harvard did this by coming up with the term ‘glycemic load’. Glycemic load is calculated simply by multiplying the GI of a food by the amount of carbohydrate per serving and dividing by 100.

For example, an apple has a GI of 40 and contains 15 grams of carbohydrate per serve. Its glycemic load is (40 x 15) ÷ 100 = 6. A potato has a GI of 90 and 20 grams of carbohydrate per serve. It has a glycemic load of (90 x 20) ÷ 100 = 18. This is not to say that the glycemic response will be exactly three times higher for a potato compared with an apple, but the total metabolic effect including overall insulin demand might be three times higher.

This text is reproduced by permission of Hodder and Stoughton Ltd from 'The New Glucose Revolution', 3rd edition, the latest publication from Professor Jennie Brand Miller et al, under a license arrangement with Food2Live.