Low-fat diets are no more effective and are sometimes less effective than other dietary interventions for long-term weight loss, according to a meta-analysis published in The Lancet Diabetes & Endocrinology.

Many randomized controlled trials have tried to show whether low-fat diets were effective for long-term weight loss, but the results have been mixed. In their study, the researchers wanted to summarize the evidence from these prior studies to determine if low-fat diets result in greater weight loss than usual diets, low-carbohydrate diets, and other higher-fat dietary interventions.

The investigators analyzed 53 studies that included a total of 68,128 adult participants. These studies included both weight-loss trials, non–weight-loss trials, and weight-maintenance trials. Diet intensity was also taken into account.

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In weight-loss trials, the researchers found that low-fat diets did not show a difference in average weight loss, compared with higher-fat diets. Compared with low-carbohydrate diets, low-fat diets actually performed worse for weight loss by an average of 1.15 kg/2.5 lbs. Low-fat diets only resulted in greater weight loss when compared with no dietary interventions at all.

In some weight-loss trials, low-fat diets actually performed worse than higher-fat diets, specifically if the two groups had a >5% difference of calories obtained from fat or when serum triglycerides differed by more than 0.06 mmol/L.

In non–weight-loss and weight-maintenance trials, low-fat and higher-fat diets had a similar effect on weight loss. There were no comparisons with low-carbohydrate diets for these trials. Again, low-fat diets only resulted in greater weight loss when compared to usual diets.

“The science does not support low-fat diets as the optimal long-term weight loss strategy. To effectively address the obesity epidemic, we will need more research to identify better approaches for long-term weight loss and weight maintenance, including the need to look beyond differences in macronutrient composition—the proportion of calories that come from fat, carbohydrate, and protein,” said Deirdre Tobias, ScD, from Brigham and Women’s Hospital and Harvard Medical School in Boston. “Long-term adherence is critical for the success of any dietary intervention, and one should also take into account other long-term health effects of his or her dietary choices.”


  1. Tobias DK, Chen M, Manson JE, et al. Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systemic review and meta-analysis. Lancet Diabetes Endocrinol. 2015; doi:10.1016/S2213-8587(15)00367-8.