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A Meta-analysis of Randomized Controlled Trials

Alain J. Nordmann, MD, MSc; Abigail Nordmann, BS; Matthias Briel, MD; Ulrich Keller, MD; William S. Yancy, Jr, MD, MSH; Bonnie J. Brehm, PhD; Heiner C. Bucher, MD, MPH

Arch Intern Med. 2006;166:285-293.

Background  Low-carbohydrate diets have become increasingly popular for weight loss. However, evidence from individual trials about benefits and risks of these diets to achieve weight loss and modify cardiovascular risk factors is preliminary.

Methods  We used the Cochrane Collaboration search strategy to identify trials comparing the effects of low-carbohydrate diets without restriction of energy intake vs low-fat diets in individuals with a body mass index (calculated as weight in kilograms divided by the square of height in meters) of at least 25. Included trials had to report changes in body weight in intention-to-treat analysis and to have a follow-up of at least 6 months. Two reviewers independently assessed trial eligibility and quality of randomized controlled trials.

Results  Five trials including a total of 447 individuals fulfilled our inclusion criteria. After 6 months, individuals assigned to low-carbohydrate diets had lost more weight than individuals randomized to low-fat diets (weighted mean difference, –3.3 kg; 95% confidence interval [CI], –5.3 to –1.4 kg). This difference was no longer obvious after 12 months (weighted mean difference, –1.0 kg; 95% CI, –3.5 to 1.5 kg). There were no differences in blood pressure. Triglyceride and high-density lipoprotein cholesterol values changed more favorably in individuals assigned to low-carbohydrate diets (after 6 months, for triglycerides, weighted mean difference, –22.1 mg/dL [–0.25 mmol/L]; 95% CI, –38.1 to –5.3 mg/dL [–0.43 to –0.06 mmol/L]; and for high-density lipoprotein cholesterol, weighted mean difference, 4.6 mg/dL [0.12 mmol/L]; 95% CI, 1.5-8.1 mg/dL [0.04-0.21 mmol/L]), but total cholesterol and low-density lipoprotein cholesterol values changed more favorably in individuals assigned to low-fat diets (weighted mean difference in low-density lipoprotein cholesterol after 6 months, 5.4 mg/dL [0.14 mmol/L]; 95% CI, 1.2-10.1 mg/dL [0.03-0.26 mmol/L]).

Conclusions  Low-carbohydrate, non–energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered.

Author Affiliations: Basel Institute for Clinical Epidemiology (Drs Nordmann, Briel, and Bucher and Ms Nordmann) and Division of Endocrinology and Metabolism (Dr Keller), University Hospital Basel, Basel, Switzerland; Department of Medicine, Department of Veterans Affairs and Duke University Medical Centers, Durham, NC (Dr Yancy); and College of Nursing, University of Cincinnati, Cincinnati, Ohio (Dr Brehm).

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