Decreases in dietary glycemic index are related to weight loss among individuals following therapeutic diets for type 2 diabetes

Abstract

This study assessed the effect of changes in glycemic index (GI) and load (GL) on weight loss and glycated hemoglobin (HbA1c) among individuals with type 2 diabetes beginning a vegan diet or diet following the 2003 American Diabetes Association (ADA) recommendations. The study was a 22-wk, randomized trial of 99 participants with type 2 diabetes who were counseled to follow 1 of 2 diet treatments. GI and GL changes were assessed based on 3-d dietary records. The relationships between GI/GL and changes in weight and HbA1C were calculated. In an intention-to-treat analysis (n = 99), the vegan group reduced GI to a greater extent than the ADA group (P < 0.05), but GL was reduced further in the ADA than the vegan group (P < 0.001). GI predicted changes in weight (P = 0.001), adjusting for changes in fiber, carbohydrate, fat, alcohol, energy intake, steps per day, group, and demographics, such that for every point decrease in GI, participants lost ~0.2 kg (0.44 lb). GI was not a predictor for changes in HbA1C after controlling for weight loss (P = 0.33). Weight loss was a predictor of changes in HbA1C (P = 0.047). GL was not related to weight loss or changes in HbA1C. A low-GI diet appears to be one of the determinants of success of a vegan or ADA diet in reducing body weight among people with type 2 diabetes. The reduction of body weight, in turn, was predictive of decreasing HbA1C.

Trial registration: ClinicalTrials.gov NCT00276939.

Conflict of interest statement

Author disclosures: G. M. Turner-McGrievy, J. Cohen, L. Gloede, and A. A. Green, no conflicts of interest. D. J. A. Jenkins reported serving on the Scientific Advisory Board of Unilever, the Sanitarium Company, and the California Strawberry Commission; receiving honoraria for scientific advice from the Almond Board of California, Barilla, and Unilever Canada; being on the speaker's panel for the Almond Board of California; and receiving research grants from Loblaws, Unilever, Barilla, and the Almond Board of California. His wife is a director of Glycemic Index Laboratories, Toronto, Ontario, Canada. N. D. Barnard is president of the Physicians Committee for Responsible Medicine and The Cancer Project, organizations that promote the use of low-fat, plant-based diets, and writes books and gives lectures about therapeutic diets, including vegan diets. He is the author of Dr. Neal Barnard’s Program for Reversing Diabetes, and receives royalties from its sales.