A new meta-analysis finds that low-carb diets are more effective than low-fat diets in weight loss and reducing cardiovascular risk. The study finding suggests “that a low-carb diet should be the first line approach for weight management,” said the first author of the study, Jonathan Sackner-Bernstein. But the difference between the two dietary approaches was not large, and the effect of both diets was modest.
The study, which was published on Tuesday in PLoS ONE, was funded by Atkins Nutritionals. A unique feature of the paper is that it contains both a classical frequentist and a Bayesian meta-analysis.
The investigators analyzed data from 1,797 obese or overweight participants in 17 randomized-controlled trials. Overall, weight was decreased by about 8 kg in the low-carb group and 6 kg in the low-fat group, resulting in a statistically significant difference between the groups of 2.04 kg. In seven trials there was a significant weight loss reduction in the low carb group, but there were no trials which found a significant benefit for the low-fat diets.
The low-fat group had a larger beneficial effect on LDL cholesterol, while the low-carb group had a better effect on HDL cholesterol, triglycerides, and systolic blood pressure:
- LDL: -1.8 mg/dl for low-carb versus -10.9 mg/dl for low fat
- HDL: 4.4 mg/dl versus -1 mg/dl
- TG: -41.1 mg/dl versus -11.3 mg/dl
- Systolic BP: -6.7 mm Hg versus -4.4 mm Hg
Both diets were associated with significant reductions in the 10-year cardiovascular risk score, but the reduction in risk was significantly greater in the low-carb group. A separate Bayesian analysis of both weight loss and cardiovascular risk found that the low-carb diet was far more likely than the low fat diet to produce the desired effects of weight loss and risk reduction.
The authors noted that weight loss may not be permanent and that it is difficult for many people to adhere to these or other diets.
At an Atkins-sponsored event in New York City to publicize the publication of the paper, Samuel Klein (Washington University) acknowledged that the differences between the groups were small, but said that the beneficial effects of even small changes should not be ignored.
Ronald Krauss (Children’s Hospital Oakland Research Institute) agreed that the results of the study were modest but said that “there is value to incremental benefits.” But, he conceded, “as a cardiologist I much prefer to treat lipids than obesity, because I know I can do something about lipids.”
One expert, who did not wish to be quoted, agreed that the small difference in weight loss was quite plausible. But, he warned, the analysis of cardiovascular risk “is a whole other story,” since the use of summary trial data to predict cardiovascular risk “is highly suspect and may not be valid” for the prediction of 10 year effects. He also questioned the role of Atkins in the study. In the paper the authors state that the company “had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.”