As if quitting smoking weren't hard enough. According to the latest research, when smokers kick the habit, they often gain as much as 20 pounds — not 5 pounds to 15 pounds, as is commonly thought.

"The findings highlight the need to provide effective dietary and physical activity counseling along with smoking cessation programs," say study authors Daniel Eisenberg of the University of Michigan and Brian Quinn of the University of California, Berkeley.

Eisenberg and Quinn reanalyzed data from the 1998 Lung Health Study, in which 5,887 American smokers were randomly assigned to a smoking cessation program and then followed for five years. The 1998 study had estimated that quitters gained nearly 12 pounds. Using a more precise statistical method, Eisenberg and Quinn found that average weight gain actually topped 21 pounds.

The larger-than-expected weight gain among ex-smokers is not just a cosmetic issue, said Robert Klesges of the University of Tennessee Health Science Center in Memphis and St. Jude Children's Research Hospital. "We're talking about a population of U.S. adults that is already overweight and obese. Incorporating weight control strategies is important to prevent future medical problems."

Klesges called for more studies on methods to reduce weight gain following smoking cessation, especially those that combine behavioral and pharmacological approaches. Some new drugs on the horizon may help with both smoking cessation and weight loss, he said.