The effectiveness of a low-fat diet on weight-loss has been debated for decades, and hundreds of randomized clinical trials aimed at evaluating this issue have been conducted with mixed results. Researchers from Brigham and Women’s Hospital (BWH) and the Harvard T.H. Chan School of Public Health (HSPH) conducted a comprehensive review of the data generated from randomized clinical trials that explored the efficacy of a low-fat diet and found that low-fat interventions were no more successful than higher-fat interventions in achieving and maintaining weight loss for periods longer than one year.

These results were published in The Lancet Diabetes & Endocrinology on Oct. 30.

“Despite the pervasive dogma that one needs to cut fat from their diet in order to lose weight, the existing scientific evidence does not support low-fat diets over other dietary interventions for long-term weight loss,” said Deirdre Tobias, ScD, a researcher in the Division of Preventive Medicine at BWH. “In fact, we did not find evidence that is particularly supportive of any specific proportion of calories from fat for meaningful long-term weight loss. We need to look beyond the ratios of calories from fat, carbs, and protein to a discussion of healthy eating patterns, whole foods, and portion sizes. Finding new ways to improve diet adherence for the long-term and preventing weight gain in the first place are important strategies for maintaining a healthy weight.”

In this meta analysis of randomized clinical trials comparing the long term effect (longer than one year) of low-fat and higher-fat dietary interventions, researchers analyzed data from 53 studies with a total of 68,128 participants that were designed to measure the difference in weight change between two groups that had a dietary intervention (low-fat or other diet). Trials that included dietary supplements or meal replacement drinks were excluded from the analysis.

On average, trial participants across all intervention groups only managed to lose and keep off six pounds at one year or longer. Compared with low-fat diets, participants in low-carbohydrate weight loss interventions were about two and a half pounds lighter after follow-up of at least one year. Researchers also report that low-fat diets led to a greater weight loss only when compared to ‘usual diet’ in which participants did not change their eating habits.

“Current evidence indicates that clinically meaningful weight loss can be achieved with a variety of dietary approaches,” said Frank Hu, senior author of the paper and Professor of Nutrition and Epidemiology at Harvard T.H. Chan School of Public Health. “The key is to improve long-term compliance and cardiometabolic health. Therefore, weight loss diets should be tailored to cultural and food preferences and health conditions of the individual and should also consider long-term health consequences of the diets.”