The U.S. Preventive Services Task Force said the guidelines echo its 2003 recommendations on screening for obesity, but take into account more recent evidence that adults can lose weight and keep it off with the right help.

"The good news is that even what you might consider to be modest rather than radical weight loss has tremendous health benefits," including lowering diabetes risk and blood pressure, said Susan Curry, a member of the task force and dean of the University of Iowa College of Public Health in Iowa City.

"Losing 5 percent of your body weight has tremendous health benefits, and intensive behavioral counseling programs help you do that and sustain it," Curry told Reuters Health. "Your primary care provider can, we hope, help you to find evidence-based programs."

The need to address weight gain nationally has grown as America tallies the health and economic costs of its obesity epidemic. More than two-thirds of the country's adults can be classified as overweight or obese.

Effective weight-loss programs, Curry said, include both nutrition and exercise support. They should help people address any barriers they have to making - and maintaining - changes in their lifestyle.

Obesity is defined as having a body mass index (a ratio of weight in relation to height) of 30 or above. That's equal to a five-foot, six-inch (168-cm) person weighing 186 pounds (84.4 kg) or a six-foot (183-cm) person at 221 pounds (100 kg).

In evidence considered by the task force, intensive behavioral programs with at least 12 sessions typically helped people lose between nine and 15 pounds (4 and 6.8 kg), or about 6 percent of their original weight.

Those types of programs may also have an effect on diabetes risk, blood pressure and stomach fat, according to the new guidelines, published Monday in the Annals of Internal Medicine bit.ly/MnBiCA. But there are still questions about any long-term impacts those interventions have on heart disease and death, for example.

DO DRUGS WORK?

The U.S. Food and Drug Administration has approved orlistat - marketed as Xenical and alli - for weight loss, but Curry and her colleagues said there wasn't enough information about how well people fare when they go off the drug to make any recommendations related to its use.

Robert Klesges, a preventive medicine researcher from the University of Tennessee Health Science Center in Memphis, said once people stop taking orlistat, they tend to gain back any weight they lost.

With behavioral interventions including lifestyle changes, "relapse" tends to be smaller, he told Reuters Health.

Klesges, who wasn't involved in the new study, recommended people trying to lose extra weight incorporate meal replacements into their diet and weigh themselves regularly.

"Exercise is very important, (but) it's much more important for weight-loss maintenance than weight loss," he said. Some of the benefits of exercise, he said, come from the fact that it's pretty difficult to eat a candy bar while running on a track, and people often don't have much of an appetite for snacking right after they work out.

The task force didn't review bariatric surgery as a potential intervention for obese people in the new guidelines.

According to data from the American Society for Metabolic and Bariatric Surgery, about 220,000 people had those procedures in 2009.

(Reporting By Michele Gershberg; Editing by Eric Walsh)

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