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?


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.


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.


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.


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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