New Study Calls Popular Diets into Question

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Dieters lost weight in the short term but regained pounds within 24 months. (Photo by Marcelo Santos/Stone/Getty Images)

"The best kept weight loss secret."

"Even after just a few days, your clothes will fit better!"

Fad diets promise the world, but a new study has demonstrated that they rarely deliver in the long run. 

Researchers at McGill University in Canada conducted clinical trials on four popular diets: Weight Watchers, the Zone, the South Beach Diet and Atkins. They discovered that dieters on these programs lost weight in the short term but regained pounds within 24 months. The study was published in Circulation: Cardiovascular Quality and Outcomes.

“Despite their popularity and their substantial contribution to the billion-dollar weight loss industry, the efficacy of these diets in promoting sustained weight loss and improving cardiovascular risk factors remains unclear,” the researchers wrote. “Our results suggest that all 4 diets are modestly efficacious for short-term weight loss, but that these benefits are not sustained long-term.”

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The results hinted that these diets might be more of a fad or gimmick than a powerful weight loss tool. Weight loss was “modest” for Atkins, Weight Watchers and Zone dieters over 12 months, the researchers said, and Atkins and Weight Watchers participants partially regained that weight lost over time.

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“Available data are conflicting and insufficient to identify one popular diet as being more beneficial than the others,” the researchers noted.

Dieters on Weight Watchers, a plan that uses a personalized point system for food, lost between 7.7 to 13.2 pounds after 12 months. Dieters in the control group who followed a traditional weight loss regimen lost an average of 1.8 to 11.9 pounds in the same time period. When the South Beach Diet – a three-step program that emphasizes good carbs, good fats, healthy sources of protein, and plenty of fiber – was tested against the control group, researchers concluded that there was little difference in weight loss over 12 months between dieters.

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"When I see a patient of mine fail at a mainstream diet, it’s because they put so much emphasis on the quantity of the calories that over time, the quality of the calories doesn’t matter anymore." (Photo by Allison Dinner/Stockfood)

Head-to-head comparisons of Atkins, Weight Watchers and the Zone with the control group yielded similar results: Atkins dieters lost an average of 4.6 to 10.3 pounds; Weight Watchers participants lost an average of 6.6 pounds; Zone dieters lost an average of 3.5 to 7 pounds and the control group lost about 4.85 pounds.

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The Atkins diet severely restricts carbohydrate intake while encouraging unlimited protein and fat consumption; the Zone diet stresses low-fat proteins, low-glycemic carbs and small amounts of good fat (avocado, olive oil, etc.)

Dr. Arthur Agatston, creator of the South Beach Diet, defended his program to Yahoo Health. “The principles of the South Beach Diet have been incorporated into almost all government and health association guidelines for healthy eating,” he said. “Randomized long-term clinical trials of diets are always suspect because participants and dietitians cannot be blinded to diet principles or to what they are eating. The entire meta-analysis is ill-conceived and should not be taken seriously by those interested in a healthy weight loss program.”

The study outcome may be disheartening to overweight and obese individuals who start these diets with intentions of significant weight loss. More than one-third of U.S. adults (78.6 million) are obese according to the Centers for Disease Control and Prevention. Approximately 17 percent (or 12.7 million) of U.S. children and adolescents aged 2 to 19 years are obese. Obesity has been linked to heart disease, stroke, diabetes, and certain types of cancer and is one of the leading causes of preventable death.

Kristin Kirkpatrick, manager of wellness nutrition services at the Cleveland Clinic Wellness Institute, said the study’s conclusions did not surprise her.

“Often times, these plans rely on either restriction of something (such as a particular food) or a limiting of something (such as calories),” she explained. “What most ‘diets’ all lack is a basic presence of trying to change lifestyle as opposed to just changing weight and at the end of the day, when I see a patient of mine fail at a mainstream diet, it’s because they put so much emphasis on the quantity of the calories that over time, the quality of the calories doesn’t matter anymore.”

She added: “These programs can be a great starting point for the beginnings of weight loss success – but eventually, a total lifestyle change (not a diet) is essential for maintaining a healthy weight and most importantly, a healthy body.”

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