Effect of a Low-Glycemic Index or a High-Cereal Fiber Diet on Type 2 Diabetes A Randomized Trial

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 participantswith 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.