Reason why a low-fat diet will not help you lose weight

Low-fat diets do not lead to greater weight loss in the long term compared to low-carbohydrate or Mediterranean diets of similar intensity, according to a major new study.

"There is no good evidence for recommending low-fat diets," said lead author Deirdre Tobias from Brigham and Women's Hospital and Harvard Medical School in US. 

Behind current dietary advice to cut out the fat, which contains more than twice the calories per gram of carbohydrates and protein, the thinking is that simply reducing fat intake will naturally lead to weight loss. But our robust evidence clearly suggests otherwise," said Tobias.

Researchers did a systematic review and meta-analysis of all randomised trials comparing the effectiveness of low-fat diets to other diets, including no diet, at improving long-term weight loss (at least 1 year) in non-pregnant adults up to the end of July 2014. They took into account the intensity of the diets which ranged from just pamphlets or instructions at the beginning of the programme to intensive multi-component programmes including counselling sessions, meetings with dieticians, food diaries, and cooking lessons.

Analysis of 53 studies involving 68,128 adults showed no difference in the average weight loss between reduced-fat diets and higher-fat diets. Indeed, reduced-fat diets only led to greater weight loss when compared with no diet at all, and resulted in less weight loss compared with low-carbohydrate interventions, although differences in weight change were small (weighted mean difference 1.15 kg). Similarly, when just considering trials without a weight loss goal (eg, those assessing lipids or cancer endpoints), participants following a reduced-fat diet lost similar amounts of weight on average compared to those on other diets. "The science does not support low-fat diets as the optimal long-term weight loss strategy," said Tobias. "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 Tobias.

"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 their dietary choices," Tobias added.

The study was published in The Lancet Diabetes and Endocrinology journal.