Effect of Legumes as Part of a Low Glycemic Index Diet on Glycemic Control and Cardiovascular Risk Factors in Type 2 Diabetes Mellitus: A Randomized Controlled Trial

Study Questions:

Legumes, including beans, chickpeas, and lentils, are among the lowest glycemic index (GI) foods, and have been recommended in national diabetes mellitus (DM) guidelines. Yet, to our knowledge, they have never been used specifically to lower the GI of the diet. What is the effect of low-GI foods on patients with type 2 DM?

Methods:

A total of 121 participants with type 2 DM were randomized to either a low-GI legume diet that encouraged participants to increase legume intake by at least 1 cup per day, or to increase insoluble fiber by consumption of whole wheat products (cereal, bread, brown rice), for 3 months. The primary outcome was change in glycated hemoglobin (HbA1c) values with calculated coronary heart disease (CHD) risk score as a secondary outcome.

Results:

Mean age was approximately 60 years, 50% were men, and mean body mass index was approximately 30 kg/m2. All were on hypoglycemic medication: at least 93% on metformin and 33% on combination with sulfonylureas. Approximately 70% were on cholesterol-lowering drugs. The low-GI legume diet reduced HbA1c values by −0.5% (95% confidence interval [CI], −0.6% to −0.4%), and the high wheat fiber diet reduced HbA1c values by −0.3% (95% CI, −0.4% to −0.2%). The relative reduction in HbA1c values after the low-GI legume diet was greater than after the high wheat fiber diet by −0.2% (95% CI, −0.3% to −0.1%; p < 0.001). The respective CHD risk reduction on the low-GI legume diet was −0.8% (95% CI, −1.4% to −0.3%; p = 0.003), largely owing to a greater relative reduction in systolic blood pressure on the low-GI legume diet compared with the high wheat fiber diet (−4.5 mm Hg; 95% CI, −7.0 to −2.1 mm Hg; p < 0.001). Other advantages of legumes include a decrease in resting heart rate and triglycerides without change in high-density lipoprotein cholesterol.

Conclusions:

Incorporation of legumes as part of a low-GI diet improved glycemic control and reduced calculated CHD risk score in patients with type 2 DM.

Perspective:

Both legumes and whole wheat carbohydrates are excellent substitutes for foods with a high GI (starches such as refined flour, white rice and potatoes, corn). Use of wheat fiber as a positive control may have minimized the treatment difference. I would guess the average diabetic adult would not be willing to consume a cup of legumes per day, but all should be advised to eat a low-GI index diet with both legumes and whole wheat carbohydrates.

Clinical Topics: Dyslipidemia, Prevention, Lipid Metabolism, Nonstatins, Diet

Keywords: Coronary Disease, Glycemic Index, Zea mays, Risk Factors, Flour, Cholesterol, Bread, Vegetables, Dietary Fiber, Triticum, Fabaceae, Starch, Cicer, Vascular Diseases, Oryza sativa, Lipoproteins, Solanum tuberosum, Lens Plant, Body Mass Index, Blood Glucose, Cereals, Hypoglycemic Agents, Food, Diet, Diabetes Mellitus


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