There is no free lunch with diet pills, new research concludes: They work much better accompanied by the hard work of dieting and exercise.

The study backed by the National Institutes of Health is the biggest and best yet to demonstrate why obese people should adopt healthful habits, even if they take weight-loss drugs, researchers said.

"If you pit this medication against your favorite all-you-can-eat buffet, the . . . buffet is going to win nine out of 10 times. So it's important you try to modify eating habits," advised University of Pennsylvania psychologist Thomas Wadden, who led the study published Thursday in the New England Journal of Medicine.

Experts have recommended that obese patients also change eating and exercise habits since doctors first began prescribing long-term weight-loss medications in the late 1990s.

In the one-year study, the most successful patients took the drug Meridia along with 30 sessions of group counseling that promoted a 1,500-calorie daily diet and half-hour walks on most days. It was especially effective when patients recorded how much they ate daily.

Obese people who took pills alone typically lost 11 pounds in the study. When they added the full program promoting lifestyle changes, they lost 27 pounds.

A third group took the drug with brief doctor's counseling, and a fourth underwent only group counseling. After a year, they were about equal with the group that only took the drug.