Famous Diets Underwhelm for CVD, Weight Control at 1 Year

Marlene Busko

November 12, 2014

BOSTON, MA — A review of 12 randomized controlled trials of four popular weight-loss diets—Atkins, Weight-Watchers, South Beach, and Zone—did not pick a "winner" in terms of sustained weight loss or improvements in cardiovascular risk factors at 1 year[1].

In fact, in head-to-head trials, at 1 year, patients had lost 1.6 to 5 kg on Atkins, Weight Watchers, and Zone diets, which was similar to the 2.2-kg loss in a control group. The diets did not have any markedly different effects on blood pressure, glycemic control, or lipid levels.

"Despite their popularity, the Atkins, South Beach, Weight Watchers, and Zone diets seem to achieve only modest sustained weight loss," Dr Mark J Eisenberg (McGill University, Montreal, Quebec) and colleagues write.

"While North Americans spend millions of dollars in the weight-loss industry, available data are conflicting and insufficient to identify one popular diet as being more beneficial than the others."

They suggest that "interventions that include dietary, behavioral, and exercise components, as well as legislative measures and industry regulations, may be better suited to the multifaceted obesity epidemic."

These guidelines already exist, Dr Robert Eckel (University of Colorado, Denver), who was not involved with this research, pointed out to heartwire . "Cardiologists and other interested healthcare providers should turn to the '2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults'[2] for information and assistance if or when needed."

The study was published online November 11, 2014 in Circulation: Cardiovascular Quality and Outcomes.

Which Diet Is Best?

The efficacy of popular commercial diets on long-term weight loss and improvements in cardiovascular risk factors is unclear, the authors write.

They aimed to examine this, with a particular focus on sustained weight loss at >12 months.

They selected four representative, popular, commercial diets: three low-carbohydrate diets (Atkins, South Beach, and Zone) and the Weight Watchers calorie-restricted diet and behavior-modification plan. They excluded the Ornish diet because it is classified by US Medicare as intended for intensive cardiac rehabilitation.

The researchers identified 12 randomized controlled trials of these four diets, which were conducted between 2003 and 2011 and enrolled 2559 patients who were followed for at least 12 months. In three trials, patients were followed for 24 months.

Five trials of the Atkins diet, four trials of Weight Watchers, and one trial of the South Beach diet compared the interventions with usual care. Two trials compared different diets (Atkins vs Weight Watchers vs Zone; and Atkins vs Zone vs control).

Patients had a median age of 45 and a median body-mass index (BMI) of 92.5 kg, and most studies were conducted in young, white, obese women.

The primary end point of the review was sustained weight loss at 12 months or longer. Secondary end points included changes in cardiovascular risk factors.

At 12 months, in the 10 trials comparing each diet vs usual care, only Weight Watchers was consistently more effective than usual care (a weight loss of 3.5 to 6 kg vs 0.8 to 5.4 kg).

However, the 24-month data from three trials suggested that the modest weight lost with Atkins or Weight Watchers was partially regained over time.

South Beach was assessed in only one long-term trial, which found no difference in weight loss vs usual care, and no data were reported on its effects on cardiovascular risk factors.

"Dearth of Data," Unsupported Claims of Diet Superiority

In an accompanying editorial[3], Dr David L Katz (Yale School of Public Health, New Haven, CT) writes that the three book-based diets in this review "are more alike than different," and "the choice of diets is rather odd, if the objective here was to examine the full expanse of competing dietary claims."

To examine weight-loss and heart-health benefits, a review should encompass "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 to lower blood pressure or prevent diabetes mellitus," he writes.

"I agree, three low-carb vs one caloric-restricted diet (Weight Watchers) seems 'odd,' but that's where the data are for [popular commercial diets] one to two years after the intervention," Eckel said. "I suspect the choices were those with sufficiently long follow-up to conclude on relative efficacy."

The review shows that "no one diet wins," Katz concludes. "But we and our patients all might, if we devoted ourselves to using what we know about the basic theme of optimal eating, allowing for variations on that theme, while tuning out the prevailing cultural static: a plethora of claims, conjoined to a dearth of data."

The study was supported by a grant from the Canadian Institutes of Health Research. The authors have reported they have no relevant financial relationships. Katz discloses that he routinely speaks about the topic of his editorial and often receives compensation for such speaking engagements.

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