Weight loss differences between these popular diets are minimal and likely of little importance to those wanting to lose weight, the researchers say. However, diets with behavioural support and exercise enhance the weight loss.
"We wanted to be the first to compare, in an evidence-based fashion, all existing randomized trials of branded diets to determine their effectiveness with regard to weight loss,” says Bradley Johnston, the study’s lead author. He is an assistant professor of clinical epidemiology of the Michael G. DeGroote School of Medicine at McMaster University, and clinical epidemiologist and scientist at The Hospital for Sick Children (SickKids).
Published today by the Journal of the American Medical Association (JAMA), the study involved a meta-analysis of 48 randomized clinical trials of branded diets, including more than 7,200 overweight and obese adults with a median age of 46 years. The research team assessed weight loss at six and 12 months.
The study was needed, adds Geoff Ball, associate professor and an obesity expert in the Faculty of Medicine & Dentistry at the University of Alberta who was involved in the study. “Given the popularity of these diets around the world, there has been a real lack of research to examine their relative benefits. But overall, the differences between the different diets regarding their impact on weight loss were relatively small.”
Johnston notes that the findings are particular to people who followed branded diets over the short-term, and who adhered to the diet. Future research may focus on long-term effectiveness, as well as on outcomes related to overall health.
At six month follow-up, people on low-carbohydrate diets lost 19 more pounds than those who were not on a diet, while those on low-fat diets lost 17 more pounds than those on no diet. After 12 months about two to three pounds of that difference was gone, and there was no difference between low-carbohydrate and low-fat diets.
Behavioural support in a diet made a difference at six months, enhancing weight loss by about seven pounds, while exercise was significant at 12 months, improving weight loss by about four and half pounds.
Branded diets included in the studies examined were Atkins, Weight Watchers, Zone, Jenny Craig, LEARN, Nutrisystem, Ornish, Volumetrics, Rosemary Conley, Slimming World and South Beach.
Source : Newswise