Introduction to the Glycemic Index

Making food choices based on Glycemic Index scores can help in the treatment of diabetes and high cholesterol levels.
Introduction to the Glycemic Index

Glycemic Index (GI) is a system that ranks carbohydrate-containing foods by their short-term effect on blood sugar. Making food choices by their GI has proven beneficial in the treatment of diabetes and high cholesterol levels.1

GI measures how much the blood sugar rises in the two- or three-hour period after eating a specific food when compared to the increase in blood sugar after eating a benchmark food (usually white bread or glucose). Foods whose carbohydrates are digested and taken up by the body quickly have a high GI score. Conversely, foods containing carbohydrates that are broken down and absorbed slowly are considered to be low GI foods.

Lists of foods with their corresponding GI values have been published.2

Foods that score higher than 70 are considered to be high GI foods. Examples of high GI foods include:
  • Rice
  • Bread
  • Potato
  • Watermelon
  • Jelly beans
Foods with scores below 55 are regarded as low GI foods. Examples include:
  • Lentil soup
  • Pasta
  • Broccoli
  • Milk
  • Grapefruit
Any foods with GI values that fall between 55 and 70 are considered intermediate. Examples include:
  • Cheese pizza
  • Sweet potato

Limitations of the GI
There are several limitations to using the GI as a method of making food choices. Preparation method and the characteristics of the carbohydrate in the food can result in different GI scores.3 For example, a ripe banana has a higher GI value than a less-ripe banana because of its higher sugar content.

Another limitation is that the GI score is determined based on a standard amount of carbohydrate (50 grams) and that amount may or may not resemble how much of the food is eaten. For example, watermelon is a high GI food but you would need to eat almost 4½ cups of it to take in the 50 grams of carbohydrate on which its GI score is based. Moreover, because every carbohydrate-containing food has a unique GI score, estimating the impact on blood sugar in a meal that contains several foods is a problem.

Glycemic Load
To address some of the limitations of the GI system, many studies use another separate, but related, term. Glycemic Load (GL) refines the concept of GI to quantify the impact that a carbohydrate-containing meal or a single food eaten in a "normal" portion has on blood sugar.4 The GL is calculated as the GI (%) multiplied by the grams of carbohydrate in the serving of food eaten. The GL for a meal would be the sum total of the GL of each food that is part of the meal.

This content is reviewed regularly. Last updated November 6, 2011.

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Other Science Library Topics:

1Opperman AM, Venter CS, Oosthuizen W, Thompson RL, Vorster HH. Meta-analysis of the health effects of using the glycaemic index in meal-planning. Br J Nutr. 2004 Sep;92(3):367-81.

2Foster-Powell K, Miller JB. International tables of glycemic index. Am J Clin Nutr. 1995 Oct;62(4):871S-890S.

3Trout DL, Behall KM, Osilesi O. Prediction of glycemic index for starchy foods. Am J Clin Nutr. 1993 Dec;58(6):873-8.

4Ebbeling CB, Ludwig DS. Treating obesity in youth: should dietary glycemic load be a consideration? Adv Pediatr. 2001;48:179-212.