What are the glycemic index and glycemic load?The glycemic index (GI) is a measure of the effects of carbohydrates on blood sugar levels. The concept was created by Dr. Jenkins and colleague in 1980-1981 at the University of Toronto. I will show the calculation so that you can understand the concept although you may not be interested in the math. The GI of a food is the area under the two hour blood glucose response curve (AUC) following the ingestion of a fixed portion of carbohydrate (50 grams). The AUC of the test food is divided by that of the standard (glucose=100, or sometimes white bread=140) and multiplies by 100. The average GI level is calculated from data collected in 10 human subjects. There are some foods containing carbohydrates which break down quickly, increasing blood glucose rapidly. They have a high GI. On the other hand, there are some foods having carbohydrates which break down slowly, increasing blood glucose gradually. They have a low GI and significant benefits for health. Glucose is defined as a glycemic index value of 100.
Glycemic index of foods Low GI (55 or less): Most fruits and vegetables (except potatoes, watermelon, carrots, grainy breads, pasta, legumes/pulses, milk, yogurt, 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, straight glucose (100). The South Beach Diet, Transitions by Market America, and NutriSystem NourishDiet. Several recent scientific evidences showed that a low GI diet significantly reduces a risk for developing type 2 diabetes and coronary heart disease. Although the research is not about human, rats fed the high GI diet were 71% fatter than the low GI group. However, for a example, although carrots have a high GI, you are unlikely to eat 50 grams of carbohydrates from them because they contain very little carbohydrates per serving. So Harvard researchers created the new concept called "glycemic load (GL)" that takes into account the amount of carbohydrates in a serving of a food. GL is calculated as the quantity (grams) of the carbohydrate content of the food, multiplied by its GI, and divided by 100. For example, the GI of a 100 grams slice serving of watermelon which has a GI of 72 and 5 grams of carbohydrates is 5*72/100=3.6. Low GL is 10 or less; Medium GL is 11-19; High GL is 20 or greater. You should check both GI and GL to determine which foods you should eat. The University of Sydney has a website where you can search 1,600 entries (www.glycemicindex.com). I will show you some examples here when 100 grams of the food is served. French baguette (white and plain): The GI is 95; The carbohydrate content is 50 grams; The GL is 48. Banana: The GI is 52; The carbohydrate content is 20 grams; The GL is 10. Carrots: The GI is 47; The carbohydrate content is 7.5 grams; The GL is 3.5. Corn tortilla: The GI is 52; The carbohydrate content is 48 grams; The GL is 25. Potato: The GI is 50; The carbohydrate content is 19 grams; The GL is 9.3. Rice (boiled white): The GI is 64; The carbohydrate content is 24 grams; The GL is 15.4 Watermelon: The GI is 72; The carbohydrate content is 5 grams; The GL is 3.6. |
