GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:
| Classification | GI range | Examples |
|---|
| Low GI | 55 or less | most fruits and vegetables (except potatoes, watermelon), grainy breads, pasta, legumes/pulses, milk, yoghurt, products extremely low in carbohydrates (some cheeses, nuts, cooking oil) |
| Medium GI | 56 - 69 | whole wheat products, basmati rice, sweet potato, table sugar |
| High GI | 70 and above | corn flakes, rice krispies, baked potatoes, watermelon, croissants, white bread, extruded breakfast cereals, most white rices (e.g. jasmine), straight glucose (100) |
|
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 experiencing hypoglycemia.
The glycemic effect of foods depends on a number of factors such as the type of starch (amylose versus amylopectin), physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal — adding vinegar, for example, will lower the GI. The presence of fat or soluble dietary fiber can slow the gastric emptying rate, thus lowering the GI. Unrefined breads with higher amounts of fiber generally have a lower GI value than white breads. Many brown breads, however, are treated with enzymes to soften the crust, which makes the starch more accessible (high GI).
While adding butter or oil will lower the GI of a meal, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel.
The glycemic index can be applied only to foods with a reasonable carbohydrate content, as the test relies on subjects consuming enough of the test food to yield about 50 g of available carbohydrate. Many fruits and vegetables (but not potatoes) contain very little carbohydrate per serving, and the average person is not likely to eat 50 g of carbohydrate from these foods. Fruits and vegetables tend to have a low glycemic index and a low glycemic load. This also applies to carrots, which were originally and incorrectly reported as having a high GI. Alcoholic beverages have been reported to have low GI values, but it should be noted that beer has a moderate GI. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%. Moderate alcohol consumption more than 12 hours prior to a test does not affect the GI.
Many modern diets rely on the glycemic index, including the South Beach Diet, Transitions by Market America and NutriSystem Nourish Diet.
The GI Symbol Program is an independent worldwide GI certification program that helps consumers identify low GI foods and drinks. The symbol is only on foods or beverages that have had their GI values tested according to standard and meet the GI Foundation's certification criteria as a healthy choice within their food group, so they are also lower in kilojoules, fat and/or salt.
Further Reading
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