Study Finds Little Difference in Effectiveness Between Branded Diets

03 Sep 2014 --- In an analysis of data from nearly 50 trials including about 7,300 individuals, significant weight loss was observed with any low-carbohydrate or low-fat diet, with weight loss differences between diet programs small, findings that support the practice of recommending any diet that a patient will adhere to in order to lose weight, according to a study in the September 3 issue of JAMA.

Named or branded (trade-marked) weight loss programs provide structured dietary and lifestyle recommendations via popular books and in-person or online behavioral support and represent a multibillion dollar industry. Debate regarding the relative merit of the diets is accompanied by advertising claiming which macronutrient composition is superior, such as a low-carbohydrate or low-fat diet. Establishing which of the major named diets is most effective is important because overweight patients often want to know which diet results in the most effective weight loss, according to background information in the article.

Bradley C. Johnston, Ph.D., of the Hospital for Sick Children Research Institute, Toronto, and McMaster University, Hamilton, Ontario, and colleagues conducted a meta-analysis to assess the relative effectiveness of different popular diets in improving weight loss. The researchers conducted a search of the medical literature to identify studies in which overweight or obese adults (body mass index 25 or greater) were randomized to a popular self-administered named diet and reported weight or body mass index data at 3-month follow-up or longer.

The meta-analysis included 59 articles that reported 48 randomized clinical trials (7,286 individuals; median age, 46 years; median weight, 207.5 lbs.). In the diet-class analysis adjusted for exercise and behavioral support, all treatments were superior to no diet at 6-month follow-up. Compared with no diet, low-carbohydrate diets had a median difference in weight loss of 19.2 lbs. and low-fat diets had similar estimated effects (17.6 lbs.).

At 12-month follow-up, the estimated average weight losses of all diet classes compared with no diet were approximately 2.2 to 4.4 lbs. less than after 6-month follow-up. The diet classes of low fat (16 lbs.) and low carbohydrate (16 lbs.) continued to have the largest estimated treatment effects.

Weight loss differences between individual diets were minimal. For example, the Atkins diet resulted in a 3.8 lbs. greater weight loss than the Zone diet at 6-month follow-up. "Although statistical differences existed among several of the diets, the differences were small and unlikely to be important to those seeking weight loss," the authors write.

"Our findings should be reassuring to clinicians and the public that there is no need for a one-size-fitsall approach to dieting because many different diets appear to offer considerable weight loss benefits. This is important because many patients have difficulties adhering to strict diets that may be particularly associated with cravings or be culturally challenging (such as low-carbohydrate diets). Our findings suggest that patients may choose, among those associated with the largest weight loss, the diet that gives them the least challenges with adherence. Although our study did not examine switching between diets, such a strategy may offer patients greater choices as they attempt to adhere to diet and lifestyle changes."

Linda Van Horn, Ph.D., R.D., of the Northwestern University Feinberg School of Medicine, Chicago, comments on the findings of this study in an accompanying editorial.

"Overall, the findings from the study by Johnston et al, along with other recent data, underscore the importance of effective diet and lifestyle interventions that promote behavioral changes to support adherence to a calorie-restricted, nutrient-dense diet that ultimately accomplishes weight loss. Choosing the best diet suited to an individual's food preferences may help foster adherence, but beyond weight loss, diet quality including micronutrient composition may further benefit longevity."