The glycemic index of foods varies according to the rate at which they release simple sugars like glucose into the bloodstream after a meal.
||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)
||56 - 69
||whole wheat products, basmati rice, sweet potato, table sugar
||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)
It is calculated as the incremental area under the two-hour blood glucose response curve (AUC) that is achieved after fasting for 12 hours and then eating a fixed amount of carbohydrate (usually 50 g). This area value is divided by the AUC of the standard defining food, which is pure glucose, and multiplied by 100. The average glycemic indexa value for a particular food is based on the values obtained for 10 humans. Both the standard and test food have to contain equal amounts of available carbohydrate.
Some of the examples of low and high glycemic index foods include:
- Foods with a low glycemic index include wholegrain bread, pulses and legumes, wheat pasta, nuts and oatmeal crackers.
- Foods with medium glycemic index include basmati rice, baked potatoes, mango, pineapple, digestives, and beans in tomato sauce.
- Foods with a high glycemic index include fresh mashed potatoes, watermelon, white rice, tapioca, corn flakes, rice krispies, weetabix, donuts, scones, rice cakes, white bread, baguette, pumpkin and parsnips.
The glycemic index of a food also depends on several other factors including:
- The entrapment of the starch molecules within the food
- The type of starch, whether amylase or amylopectin
- The fat and protein content of the food
- The presence of organic acids and their salts in the diet. For example, if vinegar is added to a meal, it lowers the glycemic index.
- The presence of fat or soluble dietary fibers can also slow the gastric emptying rate and therefore lower the glycemic index of the meal.
Reviewed by Sally Robertson, BSc