According to a new meta-analysis conducted by researchers at McMaster University in Hamilton, Canada, and published in JAMA, branded diets – such as Atkins or Weight Watchers – tend to have similar levels of effectiveness if they are adhered to.
“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 lead author Bradley Johnston, assistant professor of clinical epidemiology of the Michael G. DeGroote School of Medicine at McMaster University.
Johnston’s team performed a meta-analysis of 48 randomized clinical trials that investigated weight loss at 6 and 12 months using branded diets. Overall, the studies look at more than 7,200 overweight and obese people, who had a median age of 46.
The diets examined across the studies were Atkins, Weight Watchers, Zone, Jenny Craig, LEARN, Nutrisystem, Ornish, Volumetrics, Rosemary Conley, Slimming World and South Beach.
The researchers found that at 6 months, study participants on low-carbohydrate diets lost 19 lb more than control participants who were not on any diet. Participants on low-fat diets, meanwhile, lost 17 lb more than those on no diet.
After 12 months, however, the meta-analysis found that there was no difference between the low-carbohydrate and low-fat diets in terms of weight lost.
Also, the analysis showed that the impact different aspects of dieting had on weight loss depended on the stage of the diet. For instance, at 6 months, behavioral support was shown to enhance weight loss by about 7 lb. At 12 months, however, the impact of exercise was significant – improving weight loss by about 4.5 lb.
Researcher Geoff Ball, associate professor and obesity expert in the Faculty of Medicine & Dentistry at the University of Alberta, says of the results:
“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.”
The authors emphasize that the findings are particular to people who stuck to the branded diets over the short term. Further research is needed to examine the long-term effects of these diets and to assess what other outcomes may be related to them.
In January, Medical News Today reported on a study investigating high-protein diets, such as the Dukan diet. The researchers found that when rats were placed on an equivalent diet, they showed symptoms of significant kidney damage.
In May, a new low-carbohydrate vegan diet – dubbed the “Eco-Atkins” – was found to be effective not only in losing weight, but also at reducing the risk of heart disease. A study published in BMJ Open observed that participants who followed the diet had 10% lower cholesterol and had lost an average of 4 lb extra, compared with participants who followed a high-carbohydrate, low-fat diet.
The Weight Watchers diet, meanwhile, has previously been found – by a study published in The Lancet – to be about twice as effective for losing weight as standard weight loss care.
In that study, people following the Weight Watchers diet stayed on the diet in larger numbers, lost more fat mass and weight and had greater reductions in waist measurements than participants on the standard care program.