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Glycemic Index: The State of the Science, Part 1—The Measure and Its Variability

Jones, Julie Miller PhD, LN, CNS

doi: 10.1097/NT.0b013e31826c4fc4
Nutrition Crossfire: GI in the Spotlight

The carbohydrate (CHO) quality of food has recently been added to essential criteria used in selection of foods for the diet. The glycemic index (GI) and its cousin, glycemic load, are recommended by some as useful for this purpose. Others argue that these measures are too variable. Variability of the measures is caused by many food factors including the content and type of sugars, the proportion of the 2 starch moieties—amylose and amylopectin—and whether the starch is raw or gelatinized, the kind and degree of cooking and processing, the presence of other ingredients and macronutrients, and whether the food is eaten hot or cold or alone or with other foods. Characteristics of the person eating the food also affect the measure including foods eaten a day or more prior to the test, the degree of chewing, and the speed of ingestion and whether glucose and insulin secretion are normal. For some, the measure is not clearly understood. Some think it compares equal amounts of food or equal amounts of CHO and fail to grasp that it compares 50 g of available CHO from the test food compared with 50 g of glucose. This means that if a food is high in dietary fiber (unavailable CHO) or water, the amount of food tested can be a very large portion to get 50 g of available CHO. Furthermore, the fact that labeled values may not relate to what is actually eaten makes use of the GI difficult for consumer and patient education. Finally, diets that are low GI or glycemic load can be constructed in very healthy ways and less healthy ways, making it seem quite reasonable that conclusions about such diverse diets on various health outcomes are often extremely variable.

The basics about the glycemic index and its measurement

Julie Miller Jones, PhD, LN, CNS, is distinguished scholar and professor emerita of food and nutrition, Deptartment of Family, Consumer & Nutritional Sciences St. Catherine University, St. Paul, Minnesota. She is a food science and nutrition professional with extensive academic experience as a faculty member, author of several books, speaker at many conferences nationally and internationally, scientific advisor to many groups (including the Carbohydrate Committee of the International Life Sciences Institute), and a leader in scientific food and nutrition organizations.

This study was supported by Wheat Foods Council.

The author has no conflicts of interest to disclose.

Correspondence: Julie Miller Jones, PhD, LN, CNS, St. Catherine University, 4030 Valentine Ct, Arden Hills, MN 55112 (

© 2012 Lippincott Williams & Wilkins, Inc.