Four of the most popular current weight loss diets produce at best only modest long-term benefits, a new study published in Circulation: Cardiovascular Quality and Outcomes shows. The study also found few significant differences across the four diets, offering little hope that any one diet can produce a serious dent in the obesity epidemic.
Mark Eisenberg and colleagues systematically searched the literature for studies evaluating the effects of the Atkins, South Beach, Zone, and Weight Watchers diets. They identified 12 randomized, controlled studies with follow-up of at least 1 year. Ten studies compared one of the diets with usual care. In these trials, Weight Watchers was the only diet to consistently outperform usual care in achieving weight loss, but this difference was modest at best, yielding a 1-year weight loss range of 3.5 to 6 kg with Weight Watchers compared with 0.8 to 5.4 kg with usual care. In the two head-to-head trials, Atkins and Zone resulted in a similar but modest weight loss. Longer-term data out to 2 years — available only for the Weight Watchers and Atkins diets– showed that some of the original weight loss was regained over time. Only one small trial studied the South Beach diet.
Some of the studies also looked at the effect of the diets on cardiovascular risk factors like cholesterol and blood pressure. Consistent with the weight loss findings, there were no large differences across the diets, and the impact of the diets on these risk factors was modest at best.
The authors note that the effects of these diets in real life may be even worse than in the “ideal conditions” of randomized, controlled trials. Observational studies suggest that the effect may be even smaller in real life and that the weight loss seen in the trials “overestimates that achieved by patients seen as part of everyday clinical practice.”
The findings also appear to be consistent with a previous study that looked at earlier popular diets, including Jenny Craig, LA Weight Loss, and again, Weight Watchers. The authors of the earlier study concluded that “with the exception of 1 trial of Weight Watchers, the evidence to support the use of major commercial and self-help weight loss programs is suboptimal.”
“Despite their popularity and important contributions to the multi-million dollar weight loss industry, we still do not know if these diets are effective to help people lose weight and decrease their risk factors for heart disease,” said Eisenberg, in a press release. “With such a small number of trials looking at each diet and their somewhat conflicting results, there is only modest evidence that using these diets is beneficial in the long-term.”
In an accompanying editorial, David Katz writes that one limitation of the study is the narrow range of diets examined by the authors, since three of them represent variations on the low-carbohydrate theme. Missing from the analysis is “the full expanse of competing dietary claims,” including ”low fat as well as low carbohydrate diets; vegan and vegetarian diets; low glycemic diets; Paleo diets; Mediterranean diets and diets incubated at the National Institutes of Health.”
But Katz argues passionately that the focus on individual diets or specific macronutrients is misguided and unhelpful. He proposes a simple formula — “wholesome foods in sensible combinations”– and states that traditional diets, despite superficial differences, “are more alike than different.” Blue Zone populations — a term for the world’s healthiest and longest-lived people — “range from vegans in California, to the quintessentially Mediterranean dieters of Crete, to the traditional Asian dieters of Okinawa,” writes Katz. “The diets all emphasize foods direct from nature, a variety of plants, and none of the hyper-processed, willfully unsatiating junk that makes up so much of the typical American diet. They are all nutrient rich, high in fiber, and low glycemic. But they are not uniformly low or high in any given macronutrient. The emphasis is consistently on wholesome foods in sensible, time-honored combinations — and the macronutrients fall within broad ranges.”