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

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Abstract

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 A1c (HbA1c), with fasting blood glucose and cardiovascular disease risk factors as secondary measures.

Results

In the intention-to-treat analysis, HbA1c decreased by −0.18% absolute HbA1c units (95% confidence interval [CI], −0.29% to −0.07%) in the high–cereal fiber diet compared with −0.50% absolute HbA1c 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 HbA1c 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 HbA1c levels compared with a high–cereal fiber diet.

Trial Registration

clinicaltrials.gov identifier: NCT00438698

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