Low-fat diets do not lead to greater weight loss in the long term compared to higher-fat diets (eg, low-carbohydrate or Mediterranean diets) of similar intensity, according to a large meta-analysis involving more than 68000 adults, published in The Lancet Diabetes & Endocrinology journal.
"There is no good evidence for recommending low-fat diets," says lead author Dr Deirdre Tobias from Brigham and Women's Hospital and Harvard Medical School, Boston, USA. "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." 
Tobias and colleagues 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 68128 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/2.5 lbs). 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.
According to Dr Tobias, "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. 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."
NOTES TO EDITORS:
This study was funded by National Institutes of Health and American Diabetes Association.
 Quotes direct from author and cannot be found in text of Article.
The Lancet Diabetes & Endocrinology