The new meta-analysis was sponsored by the American Diabetes Association and the National Institutes of Health.
Ten days after a study sponsored by the creators of the Atkins Diet touted the benefits of low carbohydrate eating comes a second meta-analysis with similar findings—but an accompanying editorial that draws a very different conclusion.
The new analysis, which appeared Friday in Lancet Diabetes & Endocrinology, involved more studies and patients and used different parameters—notably, it required time frames of a year or more for the data to be included. But it reached essentially the same conclusion as a smaller analysis that appeared October 21, 2015, in PLoS ONE: diets low in carbohydrates will produce more weight loss than those low in fat.
The key difference between the 2 analyses is how they were interpreted. On the day the PLoS ONE article appeared, lead author Jonathan Sackner-Bernstein took part in a panel discussion with advocates for low carbohydrate eating at New York’s Four Seasons Hotel, and an accompanying press release called for low carbohydrate diets to be given equal weight billing in the Dietary Guidelines for Americans, which will be updated later this year. However, one of the panelists that day called efforts to update the guidelines a “fool’s errand.”
In February, the Dietary Guidelines Advisory Committee (DGAC) issued a report that called for Americans to eat less red and processed meat and to follow daily limits on sugar and saturated fat. DGAC lifted a longtime recommendation against cholesterol and said lean meat was part of a healthy diet.
The Lancet article—whose authors include Frank B. Hu, a 2015 DGAC member—says that “nutrition guidelines should cease recommending low-fat diets for weight loss in view of the clear absence of long-term efficacy when compared with other similar intensity dietary interventions.”
But is this an endorsement of the low-carb lifestyle? An accompanying editorial says no.
“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,” writes Kevin D. Hall, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases, in the editorial. (NIDDK is part of the National Institutes of Health, which funded this new meta-analysis with the American Diabetes Association.)
Hall goes on to say that, “Although statistically significant, such a miniscule 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,” noting that it averaged 3.75 kg.
The meta-analysis culled data from 53 studies involving 68,128 patients. According to the study, low-fat interventions did not lead to differences in weight change compared with other higher fat weight loss interventions, and led to greater weight decrease only when evaluated against how people usually ate.
Why don’t diets work? Hall writes that adherence likely lapsed long before the 1-year mark. “Outpatient weight loss studies ubiquitously achieve a maximum weight loss after about 6-8 months, followed by weight regain,” he wrote.
What’s needed, Hall suggests, is more research into the factors to that help people stick with a healthy diet for the long term.
Tobias DK, Chen M, Manson JE, Ludwig DS, Willett W, Hu FB. Effect of low-fat diet interventions versus other diet interventions long-term weight change in adults: a systematic review and meta-analysis [published online October 30, 2015]. Lancet Diab Endocrinol. 2015; doi:10.1016/S2213-8587(15)00367-8.
Hall KD. Prescribing low-fat diets: useless for long-term weight loss? [published online October 30, 2015]. Lancet Diab Endocrinol. 2015; doi:10.1016/S2213-9597(15)00413-1.