Glycaemic index and diabetes

Glycaemic index and diabetes

Diabetes Centre

Glycaemic index and diabetes

The Glycaemic Index or GI is an important tool in the dietary treatment of diabetes. It is not a fashion diet or fad that will be replaced by another soon − it has been scientifically tried and tested and is endorsed by the World Health Organisation.

In fact, the World Health Organisation (WHO), the highest nutrition authority in die world, states that all people, and not only those with diabetes, should eat a high carbohydrate diet based on low Glycaemic Index (GI) foods. The GI is determined by actual tests and does not rest on assumptions of what an effect a product has on blood glucose.

Development of the index

In the past, it was thought that complex carbohydrates or starches, such as potatoes, rice and bread were slowly digested and absorbed and therefore only caused a slight rise in blood glucose levels. Simple sugars were assumed to have the opposite effect (absorbed and digested quickly, causing a rapid rise in blood glucose). However, this idea was challenged and researchers started testing how various carbohydrates affect the blood glucose levels. Eventually the GI was proposed by Dr David Jenkins of the University of Toronto, Canada, in 1981.

What is the GI?

The GI can be described as a numerical measure (from 0 to 100) of the effects of carbohydrates in food on blood sugar levels. The number for glucose, which is absorbed quickest, is set at 100 and all other carbohydrates are measured and rated relative to this number. Each type of food, independent of the amount of food consumed, has its own measure.

What does it mean in practice? If you eat two or three Super C sweets or some pure glucose, the glucose will be absorbed immediately and raise your blood sugar levels significantly within 10 minutes. The glucose from an apple, with a GI of 36, will take much longer to enter your bloodstream so that your blood sugar levels will not be raised too high or too suddenly. Therefore, eating low GI foods will help to keep your blood glucose levels even. High GI foods, on the other hand, may play havoc with you blood sugar levels.

Advantages of consuming low GI foods

  • It promotes a more moderate rise in blood glucose level which is sustained over a longer period of time, keeping the body’s metabolic processes and energy levels balanced
  • It assists with weight loss and maintenance of healthy weight. You will feel fuller for longer periods of time after eating
  • It is gentler on the pancreas as less insulin is needed
  • It helps to lower and control ‘bad’ cholesterol levels
  • It lowers the risk of type 2 diabetes (those who have followed a diet of low GI foods for several years have a significantly lower risk of getting type 2 diabetes) and for those already suffering from diabetes, it can help control the condition
  • It improves physical endurance, as blood glucose levels are kept at a moderate level (instead of dipping drastically due to sudden insulin production) for a more sustained period of time. (When exercising, intermediate and high GI foods can be used during and after training to ensure that both the liver and muscle glycogen is replenished without the blood sugar being affected.)
  • Low-GI foods help to maintain and increase the body’s sensitivity to insulin while high-GI foods lower it in the long run
  • It lowers the risk of heart disease (those who have followed a diet of low GI foods for several years have a significantly lower risk of getting coronary heart disease
  • There is also a decreased risk of cancer, according to a study in Australia.

Factors that affect the GI of a food

 Although low GI is a wonderful tool in the management of diabetes, it is limited by several factors, such as the following:

  • The glycemic response is different from one person to another, and even in the same person from day to day, depending on blood glucose levels, insulin resistance, and other factors.
  • Many foods found to have a low GI are in fact high in soluble fibre (oats and legumes). Insoluble fibre in wheat does not usually have a lowering effect on the GI, unless the grain is intact.
  • Both fat and protein slow the rate of digestion. Mixed meals containing small amounts of protein and fat will lower the GI of the meal. A peanut butter sandwich is more slowly absorbed than bread on its own because the protein and fat in the peanut butter slow down the digestion of the whole sandwich.
  • When cooked starch cools down, and a resistant starch develops that has a lower GI index than the hot equivalents. Cold mealie pap and cold sweetened custard both have lower GIs than their hot equivalents.
  • Cooking and processing methods alter the structure of food. For example, stewed apples and cooked oats porridge have a higher GI than raw fresh apple and raw oats. Milling and grinding grains to make fine flour makes the food particles easier to digest, so all fine flours and their products have high GIs, even whole wheat bread and nutty wheat.
  • Blood glucose levels rise slower if you eat more slowly. The new motto in meal planning should be low GI, low fat and high in fibre and low in salt.