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A Randomized Trial

David J. A. Jenkins, MD; Cyril W. C. Kendall, PhD; Gail McKeown-Eyssen, PhD; Robert G. Josse, MB, BS; Jay Silverberg, MD; Gillian L. Booth, MD; Edward Vidgen, BSc; Andrea R. Josse, MSc; Tri H. Nguyen, MSc; Sorcha Corrigan, BSc; Monica S. Banach, BSc; Sophie Ares, MA, RD, CDE; Sandy Mitchell, BASc, RD; Azadeh Emam, MSc; Livia S. A. Augustin, MSc; Tina L. Parker, BASc, RD; Lawrence A. Leiter, MD

JAMA. 2008;300(23):2742-2753.

Context  Clinical trials using antihyperglycemic medications to improve glycemic control have not demonstrated the anticipated cardiovascular benefits. Low–glycemic index diets may improve both glycemic control and cardiovascular risk factors for patients with type 2 diabetes but debate over their effectiveness continues due to trial limitations.

Objective  To test the effects of low–glycemic index diets on glycemic control and cardiovascular risk factors in patients with type 2 diabetes.

Design, Setting, and Participants  A randomized, parallel study design at a Canadian university hospital research center of 210 participants with type 2 diabetes treated with antihyperglycemic medications who were recruited by newspaper advertisement and randomly assigned to receive 1 of 2 diet treatments each for 6 months between September 16, 2004, and May 22, 2007.

Intervention  High–cereal fiber or low–glycemic index dietary advice.

Main Outcome Measures  Absolute change in glycated hemoglobin A_1c (HbA_1c), with fasting blood glucose and cardiovascular disease risk factors as secondary measures.

Results  In the intention-to-treat analysis, HbA_1c decreased by –0.18% absolute HbA_1c units (95% confidence interval [CI], –0.29% to –0.07%) in the high–cereal fiber diet compared with –0.50% absolute HbA_1c units (95% CI, –0.61% to –0.39%) in the low–glycemic index diet (P < .001). There was also an increase of high-density lipoprotein cholesterol in the low–glycemic index diet by 1.7 mg/dL (95% CI, 0.8-2.6 mg/dL) compared with a decrease of high-density lipoprotein cholesterol by –0.2 mg/dL (95% CI, –0.9 to 0.5 mg/dL) in the high–cereal fiber diet (P = .005). The reduction in dietary glycemic index related positively to the reduction in HbA_1c concentration (r = 0.35, P < .001) and negatively to the increase in high-density lipoprotein cholesterol (r = –0.19, P = .009).

Conclusion  In patients with type 2 diabetes, 6-month treatment with a low–glycemic index diet resulted in moderately lower HbA_1c levels compared with a high–cereal fiber diet.

Trial Registration  clinicaltrials.gov identifier: NCT00438698

Author Affiliations: Clinical Nutrition and Risk Factor Modification Center (Drs Jenkins, Kendall, R. Josse, and Leiter, and Messrs Vidgen and Nguyen, and Mss Corrigan, Banach, Ares, Mitchell, Emam, Augustin, and Parker) and Division of Endocrinology and Metabolism (Drs Jenkins, R. Josse, and Leiter), St Michael's Hospital, Toronto, Ontario; Dalla Lana School of Public Health (Dr McKeown-Eyssen), Department of Nutritional Sciences (Drs Jenkins, Kendall, McKeown-Eyssen, R. Josse, and Leiter, and Messrs Vidgen and Nguyen, and Mss A. Josse, Banach, Emam, and Augustin), and Department of Medicine (Drs Jenkins, R. Josse, Silverberg, Booth, and Leiter), University of Toronto, Toronto, Ontario; Sunnybrook and Women's College Health Sciences Center, Toronto, Ontario (Dr Silverberg); and College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan (Dr Kendall), Canada.

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