Glycemic index, also called glycaemic index (GI), is a ranking system for carbohydrates based on their effect on blood glucose levels in the first two hours after eating. It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of post-meal (medically called: postprandial) glycemia. The concept of glycemic index was developed by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto.
Glycemic index has been described in these words: "The glycemic index (GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. Low GI diets have been shown to improve both glucose and lipid levels in people with diabetes (type 1 and type 2). They have benefits for weight control because they help control appetite and delay hunger. Low GI diets also reduce insulin levels and insulin resistance."
Glycemic index of foodsEdit
GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:
|Low GI||55 or less||most fruit and vegetables (but not potato), oats, buckwheat, whole barley, All-bran, Basmati rice|
|Medium GI||56 - 69||sucrose, Mars bar, croissant|
|High GI||70 or more||corn flakes, baked potato, Jasmine rice, white bread|
A low GI food will release glucose more slowly and steadily. A high GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after endurance exercise or for a person with diabetes experiencing hypoglycemia.
Glycemic index may is used to determine the suitability of diet in person with conditions of obesity, diabetes and heart disease. Recent studies from Harvard School of Public Health  "indicate that the risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the GI of the overall diet. In 1999, the World Health Organisation (WHO) and Food and Agriculture Organisation (FAO) recommended that people in industrialised countries base their diets on low-GI foods in order to prevent the most common diseases of affluence, such as coronary heart disease, diabetes and obesity."
Some of the benefits of eating foods with low GI carbohydrates:
- It contributes to weight control and weight loss
- It increases the body's sensitivity to insulin
- It improves diabetes control
- It reduces the risk of heart disease
- It reduces blood cholesterol levels
- It reduce hunger and keep you fuller for longer
- It prolongs physical endurance
- It helps in re-fuelin carbohydrate stores after exercise
The glycemic index has been criticised for the following reasons:
- The GI does not take into consideration other factors besides glycemic response, such as insulin response.
- The GI of a food varies depending on the kind of food, its ripeness, the length of time it was stored, how it was cooked, its variety, etc., and how it was processed or manufactured.
- The GI of a food varies from person to person and even in a single individual from day to day, depending on blood glucose levels, insulin resistance, and other factors.
- The GI of a mixed meal can be difficult to predict.
- The GI value is based on a portion that contains 50 grams of carbohydrate only.
This criticism can be addressed by taking the Glycemic load (that is, ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size) into account. This combined approach is, however, somewhat more complicated, and therefore harder to use in giving dietary advice.
The comparison of foods that behave differently by a common consideration of the area under their blood glucose curves has no scientific basis and is fundamentally incorrect. Liquid foods or easilly dissolved foods where all carbohydrate is immediately available for conversion to glucose cannot be compared to solids where only the surface of the food is immediately available and a further portion released later . The curve for solids will be extended in time due to the delayed release of carbohydates and thus always give a larger area than liquids. A recent study considering this issue based on the consolidated test results of over 600 foods concluded that the GI significantly underestimated the glycemic effect of liquids and readilly dissolved substanced and that real GI of sugar and its close cousin fruit juice should be around 100 and 80 respectively. The implications of this are simply mind blowing. Full details are available at http://sites.google.com/site/bangkatanfiles