Clinical Question

Is a low-fat or a low-carbohydrate diet more effective in causing weight loss and improving cardiovascular disease risk?

Bottom Line

More than 40 years ago, Dr. Robert Atkins wrote his first book advocating for a low-carbohydrate diet to cause and sustain weight loss. This study (of mostly women) found that a low-carbohydrate diet—though not as severe a diet as the Atkins approach—caused an average 3.5 kg (7.7 lb) greater weight loss than a low-fat diet. Both diet approaches were undertaken without any caloric restriction; in other words, these were low-carbohydrate and low-fat, not low-calorie, diets. (Level of Evidence = 1b–)

Synopsis

The 148 participants were volunteers from the general public: 88% were women and 50% were black. They were randomized, concealed allocation uncertain, to a diet of fewer than 40 g of carbohydrates per day (the Atkins diet suggests fewer than 20 g per day) or a diet aimed to keep fat to less than 30% of daily energy intake, which is in line with the diet recommended by the National Cholesterol Education Program in the United States. Neither diet included a specific calorie goal.

Participants in both groups received significant counseling consisting of individual weekly sessions with a dietitian for the first four weeks followed by small-group counseling sessions every other week for the next five months. At 12 months, the low-carbohydrate diet group lost an average of 3.5 kg more than the low-fat diet group (−5.3 vs. −1.8 kg [−11.7 vs. −4.0 lb]). They also had greater reductions in fat mass and higher gains in lean mass. Although total cholesterol levels did not markedly change in either group, high-density lipoprotein levels increased significantly more in the low-carbohydrate group, and triglyceride levels decreased significantly more in that group, as well. Blood pressure, glucose levels, and insulin levels were not different between the groups.

Study design: Randomized controlled trial (nonblinded)

Funding source: Government

Allocation: Uncertain

Setting: Outpatient (any)

Reference: BazzanoLAHuTReynoldsKet alEffects of lowcarbohydrate and low-fat diets: a randomized trial. Ann Intern Med.2014; 161( 5): 309– 318.