The Effect of a Low-Carbohydrate, Ketogenic Diet Versus a Low-Glycemic Index Diet on Glycemic Control in Type 2 Diabetes Mellitus

Eric C Westman; William S Yancy Jr; John C Mavropoulos; Megan Marquart; Jennifer R McDuffie


Nutr Metab 

In This Article

Abstract and Background


Objective: Dietary carbohydrate is the major determinant of postprandial glucose levels, and several clinical studies have shown that low-carbohydrate diets improve glycemic control. In this study, we tested the hypothesis that a diet lower in carbohydrate would lead to greater improvement in glycemic control over a 24-week period in patients with obesity and type 2 diabetes mellitus.
Research Design and Methods: Eighty-four community volunteers with obesity and type 2 diabetes were randomized to either a low-carbohydrate, ketogenic diet (< 20 g of carbohydrate daily; LCKD) or a low-glycemic, reduced-calorie diet (500 kcal/day deficit from weight maintenance diet; LGID). Both groups received group meetings, nutritional supplementation, and an exercise recommendation. The main outcome was glycemic control, measured by hemoglobin A1c.
Results: Forty-nine (58.3%) participants completed the study. Both interventions led to improvements in hemoglobin A1c, fasting glucose, fasting insulin, and weight loss. The LCKD group had greater improvements in hemoglobin A1c (-1.5% vs. -0.5%, p = 0.03), body weight (-11.1 kg vs. -6.9 kg, p = 0.008), and high density lipoprotein cholesterol (+5.6 mg/dL vs. 0 mg/dL, p < 0.001) compared to the LGID group. Diabetes medications were reduced or eliminated in 95.2% of LCKD vs. 62% of LGID participants (p < 0.01).
Conclusion: Dietary modification led to improvements in glycemic control and medication reduction/elimination in motivated volunteers with type 2 diabetes. The diet lower in carbohydrate led to greater improvements in glycemic control, and more frequent medication reduction/elimination than the low glycemic index diet. Lifestyle modification using low carbohydrate interventions is effective for improving and reversing type 2 diabetes.


The dietary macronutrient that raises postprandial serum glucose and insulin most potently is carbohydrate.[1] This observation led to the use of diets low in carbohydrate for the treatment of diabetes before insulin or other medication therapies were available.[2] In like fashion, individuals who are insulin-deficient are instructed to estimate the amount of carbohydrate in the meal and then to administer the insulin dosage based upon the amount of dietary carbohydrate. This strong relationship between dietary carbohydrate and postprandial serum glucose led to the development of medications that block carbohydrate absorption for the treatment of type 2 diabetes.[3]

Clinical studies that have lowered the percentage of dietary carbohydrate and/or the glycemic index of the carbohydrate have consistently shown improvements in glycemic control among individuals with type 2 diabetes.[4,5,6,7,8] In randomized studies, low-carbohydrate diets have been found effective for the treatment of obesity for durations up to 24 months.[9] While glycemic control was not a primary outcome, some of these studies additionally demonstrated improvement in glycemic parameters when carbohydrate intake was lowered. In the Nurse's Health Study cohort study, low-glycemic load diets were found to be associated with lower cardiac risk over a 20 year period.[10] One mechanism to explain these findings is that when patients are instructed to limit carbohydrate intake to low levels without mention of caloric intake, there is an overall reduction in caloric intake.[11]

In several recent studies, in the outpatient setting and metabolic ward, low-carbohydrate ketogenic diets led to improvements in glycemic control among patients with diabetes.[12,13,14,15,16] While it may be intuitive that a low-carbohydrate ketogenic diet with fewer than 20 grams of carbohydrate intake per day would lead to better glycemic control than a "low-glycemic diet", we are not aware that this idea has been actually tested. In the present study, our hypothesis was that a diet lower in carbohydrate would lead to greater improvement in glycemic control in patients with obesity and type 2 diabetes mellitus over 24 weeks in the outpatient setting.


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