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Title: LETTER TO THE EDITOR IN REBUTTAL TO "INFLUENCE OF GLYCEMIC INEX/LOAD ON GLYCEMIC RESPONSE, APPETITE, AND FOOD INTAKE IN HEALTHY HUMANS"

Author
item LUDWIG, DAVID - CHILDRENS HOSPITAL BOSTON
item Roberts, Susan

Submitted to: Diabetes Care
Publication Type: Other
Publication Acceptance Date: 9/22/2005
Publication Date: 2/1/2006
Citation: Ludwig, D.S., Roberts, S.B. 2006. Letter to the editor in rebuttal to "Influence of Glycemic Inex/Load on Glycemic Response, Appetite, and Food Intake in Healthy Humans". Diabetes Care. 28: 2123-2129.

Interpretive Summary:

Technical Abstract: In their recent article, Alfenas and Mattes(1) conclude that the glycemic index values (GI) of individual foods do not predict glycemic response (GR) to mixed meals, nor influence measures of hunger. Because the observed GR did not differ between diets, the lack of effect on appetite is not surprising. Thus, the potentially important aspect of the study pertains to the prediction of GI in mixed meals. The authors approach was to validate published GI values in a pretest, selecting 48 of 79 foods with "consistent GRs." However, their methods do not conform to standard procedures(2-4). Only 3 subjects were used for each food, instead of the recommended number of 10(3). Blood glucose was measured by glucometer, a device that is not sufficiently accurate in the normal range for research purposes(4). With such small subject number, confidence interval around the mean would likely overlap for most foods on both diets. From a statistical perspective, the selection of foods with an underpowered pretest using inaccurate methods would produce regression to the mean. It is important to emphasize that published values for specific foods cannot be used for a study such as this without careful validation because: published values may not have been determined correctly; the composition or manufacturing procedures of individual products may change over time; and shelf life and preparatory methods may also affect GI. Such concerns are not unique to studies of GI. One can't assume, for example, that a published value for vitamin C content of Valencia orange will apply to every piece of fruit, at all times of year, from any location. Major categories of food differ in GI with reasonable consistency: most fruits, legumes, minimally processed grain products and pasta prepared from hard wheat have low to moderate GI; whereas highly processed grains products and pasta previously prepared and canned have a high GI. Most of the foods used by Alfenas and Mattes for the low GI diet included highly processed grain products (quick pizza, quiche, pita, bagel, etc.). There are many studies demonstrating that the GI of individual foods predicts response to mixed meals when appropriate methodology is utilized(5-7). With regard to the authors' description of our study, two of the test meals did have identical macronutrient composition and solid food components, and the measured GR corresponded closely with prediction (8). Clearly, research into the relationship between GI and GR merits study. To advance the dialogue, adequately-powered studies employing accepted methodology will be needed. A more fundamental question is whether diets comprised of low GI foods improve important clinical endpoints related to obesity, diabetes, heart disease and cancer. (1)Alfenas RCG, Mattes RD. Influence of glycemic inex/load on glycemic response, appetite, and food intake in healthy humans. Diabetes Care 2005, 28: 2123-2129. (2)Wolever TM, Vorster HH, Bjorck I, et al. Determination of the glycaemic index of foods: interlaboratory study. Eur J Clin Nutr 2003, 57:475-82. (3)Brouns F, Bjorck I, Frayn KN et al. Glycaemic index methodology. Nutr Res Rev 2005, 18:145-171. (4)Velangi A, Fernandes G, Wolever TM. Evaluation of a glucose meter for determining the glycemic response of foods. Clin Chim Acta 2005, 356:191-8. (5)Wolever TM, Bolognesi C. Prediction of glucose and insulin responses of normal subjects after consuming mixed meals varying in energy, protein, fat, carbohydrate and glycemic index. J Nutr 1996, 126:2807-12. (6)Chew I, Brand JC, Thorburn AW, Truswell AS. Application of glycemic index to mixed meals. Am J Clin Nutr 1988, 47:53-56. (7)Bornet FR, Costagliola D, Rizkalla SW et al. insulinemic and glycemic indexes of six starch-rich foods taken alone and in mixed meal by type 2 diabetics. Am J Clin Nutr 1987, 45:588-595. (8)Ludwig DS, Majzoub JA, Al-Zahrani A, Dallal G, Bl