A low-fat diet was the least effective form of weight loss intervention and showed superior weight loss only when compared with a usual diet, according to a systematic review by Dr. Deirdre Tobias and her associates.
A total of 53 studies were included in the review and meta-analysis. Low-carbohydrate diets were more effective than low-fat diets, with a weighted mean difference of 1.15 kg. There was no significant difference between low-fat diets and other higher-fat weight loss interventions. A low-fat diet was more effective then remaining on a usual diet, with a weighted mean difference of 5.41 kg.
While on average, low-fat and higher-fat weight loss interventions were statistically similar, if low-fat and higher-fat groups differed in calories obtained from fat by more than 5% or in serum triglyceride levels of at least 0.06 mmol/L, higher-fat interventions became more effective, with weighted mean differences of 1.04 kg and 1.38 kg, respectively, the investigators found.
While low-carbohydrate diets were statistically more effective than were low-fat diets, Dr. Kevin Hall of the National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Md., wrote in a related comment, “Consider the magnitude of the benefit: Participants prescribed low-carbohydrate diets lost only about 1 kg of additional weight after 1 year compared with those advised to consume low-fat diets. Although statistically significant, such a minuscule difference in weight loss is clinically meaningless. Furthermore, irrespective of the diet prescription, the overall average weight loss in trials testing interventions designed to reduce bodyweight was unimpressive.”
Find the full study in the Lancet Diabetes and Endocrinology (doi: 10.1016/S2213-8587[15]00367-8).