Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial

Study Questions:

How do diets low in carbohydrates compare to a low-fat diet in terms of body weight and cardiovascular risk factors?

Methods:

Participants were enrolled in this randomized controlled trial between 2008 and 2011, which was conducted in one academic medical center. Men and women (ages 22-75 years) with a mean body mass index (BMI) between 30 and 45 kg/m2 and without known cardiovascular disease or diabetes at baseline were included in the study. Participants were randomized to either a low carbohydrate (<40 g/d) or low-fat (<30% of daily energy intake from total fat [<7% saturated fat]) diet. Both groups received dietary counseling at regular intervals throughout the trial. Data on weight, cardiovascular risk factors, and dietary composition were collected at 0, 3, 6, and 12 months.

Results:

A total of 148 participants (mean age, 46.8 years; 88% female; 51% black) were included. Sixty participants (82%) in the low-fat group and 59 (79%) in the low-carbohydrate group completed the intervention. At 12 months, participants on the low-carbohydrate diet had greater decreases in weight (mean difference in change, -3.5 kg [95% confidence interval {CI}, -5.6 to -1.4 kg]; p = 0.002), fat mass (mean difference in change, -1.5% [CI, -2.6% to -0.4%]; p = 0.011), ratio of total–high-density lipoprotein (HDL) cholesterol (mean difference in change, -0.44 [CI, -0.71 to -0.16]; p = 0.002), and triglyceride level (mean difference in change, -0.16 mmol/L [-14.1 mg/dl] [CI, -0.31 to -0.01 mmol/L {-27.4 to -0.8 mg/dl}]; p = 0.038) and greater increases in HDL cholesterol level (mean difference in change, 0.18 mmol/L [7.0 mg/dl] [CI, 0.08 to 0.28 mmol/L {3.0 to 11.0 mg/dl}]; p = 0.001) than those on the low-fat diet.

Conclusions:

The investigators concluded that the low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrates may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.

Perspective:

These data provide support for a low-carbohydrate diet. Larger trials will be needed to confirm these results. In addition, examining how fiber and type of carbohydrates impact on these findings is warranted.

Clinical Topics: Diabetes and Cardiometabolic Disease, Dyslipidemia, Prevention, Hypertriglyceridemia, Lipid Metabolism, Nonstatins, Diet

Keywords: Body Mass Index, Weight Loss, Cardiovascular Diseases, Energy Intake, Risk Factors, Cholesterol, HDL, Confidence Intervals, Diet, Fat-Restricted, Triglycerides, Diabetes Mellitus, Dietary Carbohydrates


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