Research at the Lady Davis InstituteSpring 2015

Long-term benefit of popular diets
still up in the air

In the short term, popular commercial diets can probably help in losing weight—but keeping it off is another matter. According to research led by Dr. Mark Eisenberg, a JGH cardiologist and an epidemiologist in the Lady Davis Institute at the JGH, it’s still unclear whether the weight stays off after the first year, and whether these diets have a positive impact on heart health.

With nearly 70 per cent of American adults overweight or obese—and, therefore, at higher risk for health problems such as heart disease, stroke, high blood pressure and diabetes—the effectiveness of diets has become a prominent public-health concern.

“Despite their popularity and important contributions to the multi-million-dollar weight loss industry, there is only modest evidence that using these diets is beneficial in the long term,” says Dr. Eisenberg.

After analyzing clinical trials on four popular diet plans—Atkins, South Beach, Weight Watchers, and Zone—that promote weight loss and improved cardiovascular health, researchers arrived at the following conclusions:

  • In trials that compared Weight Watchers to usual care (which includes low-fat diets, behavioural weight-loss intervention, nutritional counseling, and self-help materials), Weight Watchers dieters lost an average of 7.7 to 13.2 pounds after one year, compared to 1.8 to 11.9 pounds with usual care. However, after two years, the lost weight was partially regained.
  • Results from trials on the Atkins diet were inconsistent. In the only trial comparing the South Beach diet to usual care, no difference in weight loss occurred in a year. However, the participants in this study were severely obese and had undergone gastric bypass surgery.
  • Trials involving head-to-head comparisons of Atkins, Weight Watchers, Zone and usual care suggest that all four result in a modest weight loss at one year, as did those in the control group who received the usual care.
  • In studies involving head-to-head comparisons, there were no marked differences between Atkins, Weight Watchers and Zone at improving cholesterol, blood pressure, blood sugar levels or other cardiovascular risk factors.

“A broader lifestyle intervention, which involves doctors and other healthcare professionals, may be more effective,” Dr. Eisenberg adds. “This tells doctors that popular diets on their own may not be the solution to help their patients lose weight.”

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