Overweight people who opt for a commercial diet plan may be more likely to stick with the program if they’re part of a group.

That’s the news from Helen Truby, RD, and her colleagues at England’s University of Surrey as reported in the journal BMJ.

Truby’s team studied nearly 300 people with overweight or obese BMI (body mass index) scores. The BBC -- a British TV network -- created a weight loss TV reality show featuring 15 of the study’s participants.

The study was designed to answer three key questions: Would commercial diets help people lose weight? How much weight would they lose? And how long would those pounds stay off?

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6-Month Effort

Participants were judged overweight or obese based on their BMI, a measure that relates weight to height. A BMI of 25 to 29.9 is considered overweight; one of 30 or more is considered obese. Participants in Truby’s study had BMIs of 27 to 40.

Participants were assigned to spend six months on one of four popular weight loss plans:

--Weight Watchers

--Atkins diet

--Slim-Fast meal replacement plan

--Rosemary Conley’s “Eat Yourself Slim Diet and Fitness Plan” (a British low-fat diet and exercise program)

For comparison, one other group was asked to eat and exercise as usual.

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Weight Changes

After six months, all groups -- except the one used for comparison -- had lost weight and fat.

How much did they lose? The average over six months was about 13 pounds. More than 9 pounds of that was fat, the study showed.

Each of the diet groups lost similar amounts of weight and fat. Those on the Atkins diet did show greater weight loss in the first two months, but the other groups caught up after that.

Researchers suspected the media attention might have motivated the participants featured on the BBC’s TV show, so they skipped those participants and rechecked the results. The findings didn’t change.

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Long-Term Results

But the extra pounds often come back after weight loss. Truby’s team sought to gather the weight and dieting behavior of participants a year after the study’s start.

About half of the original group (158) took the researchers up on that offer. Of those, “only 58 … were still keeping to their allocated diets,” write Truby and colleagues.

People in the Weight Watchers and Rosemary Conley programs -- which both involved group meetings -- were more likely to have stuck with their programs for a year.

One year later, nine participants reported sticking with the Atkins diet; nine kept using Slim-Fast; 20 were steadfast in the Weight Watchers group, and another 20 in the Rosemary Conley plan.

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Calls for a Sequel

Even after six months, the dropout rate was “sobering,” notes David Arterburn, MD, MPH, in a journal editorial. Arterburn works in Seattle at the Group Health Center for Health Studies. He was not involved in Truby’s study.

The low one-year follow-up rate makes it impossible to draw inferences about the long-term effectiveness of the diet plans,” Arterburn adds.

Of course, weight loss doesn’t require a commercial program. Check with your doctor for pointers on getting started.

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By Miranda Hitti, reviewed By Ann Edmundson, MD

SOURCES: Truby, H. BMJ, June 3, 2006; vol 332: pp 1309-1311. Arterburn, D. BMJ, June 3, 2006; vol 332: pp 1284-1285. News release, BMJ.