1. In this systematic review and meta-analysis of randomized controlled trials, low-fat diet was not found to be superior to higher-fat dietary interventions for long-term weight loss.
2. Low-carbohydrate diets, when compared to low-fat diets, led to significantly greater weight reduction.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Dietary interventions targeted at weight loss vary considerably in intensity, macronutrient restrictions, and efficacy. The presumed effectiveness of low-fat diets for weight reduction has been previously called into question. In this study by Tobias et al., investigators set out to analyze randomized controlled trials that compared low and high-fat dietary interventions. Some of these diets were aimed towards an endpoint of weight loss; however, studies with other endpoints (e.g. lipid reduction) were included as well. 53 trials, found using an extensive database search, were included in the meta-analysis. The investigators hypothesized that when other factors were controlled for, low-fat diets would not be more efficacious than high-fat diets for long-term reduction of bodyweight. The results demonstrated that when diets were of similar intensity, low-fat diets were no more efficacious than high-fat or low-carbohydrate diets for long-term weight loss. Low-carbohydrate diets led to significantly more weight loss than low-fat diets. The findings indicate that a reevaluation of currently prescribed low-fat diets may be warranted. The study was strengthened by the large number of participants included in the final analyses (more than 60,000). Results may be weakened by a high potential source of bias for 39 trials, in which the drop-out and loss-to-follow-up rates exceeded 5%.
The study was funded by National Institutes of Health and American Diabetes Association.
In-Depth [systematic review and meta-analysis]: This study is a systemic review and meta-analysis of randomized controlled trials. The study aimed to investigate the effectiveness of low-fat diets in producing long-term weight reduction, compared to diets of similar intensity. In total, 53 trials were included in the final analysis with 68128 participants.
The results demonstrated no significant difference between low-fat and higher-fat dietary interventions in producing long-term weight loss (19 comparisons; weight-mean difference [WMD] 0.36 kg, 95% CI [–0.66 to 1.37). The study noted significant between-study heterogeneity in the low-fat and high-fat randomized trials. Low-carbohydrate diets was found to be associated with more significant weight-loss than low-fat diets (WMD 1.15 kg [95% CI 0.52 to 1.79]), with minimal between-study heterogeneity.
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