Smokers who successfully quit for a year can expect, on average, to gain more than 10 pounds over that time, researchers reported.
The figure, from a meta-analysis of smoking cessation studies, is sharply higher than the oft-quoted 6.4-pound gain that quitters can expect, according to Henri-Jean Aubin, MD, PhD, of Hôpital Paul Brousse in Villejuif, France, and colleagues.
But variation among smokers is very wide, with about 16% losing weight after a year of abstinence and about 13% gaining more than 22 pounds, Aubin and colleagues reported online in BMJ.
While previous studies have underestimated the amount of expected weight gain after quitting smoking, Aubin and colleagues argued that "doctors might usefully give patients a range of expected weight gain."
And they suggested that further research is needed to help pick out smokers at greatest risk for weight gain and to clarify ways to keep the pounds off.
It also will be important for doctors to emphasize that fear of gaining weight is not a good reason to keep smoking, argued Esteve Fernández, MD, PhD, of the Universitat de Barcelona in Barcelona, Spain, and Simon Chapman, PhD, of the University of Sydney in Sydney, Australia.
In an accompanying editorial, they noted that obesity is associated with an increased risk of all-cause mortality, but studies suggest that "modest weight gain does not increase the risk of death."
"Smoking does," they concluded.
The researchers included 62 studies in their analysis, including those that compared various pharmacological methods of smoking cessation with placebo, or looked at ways of preventing weight gain after quitting.
The primary analysis was of those who quit without treatment – in essence, successful quitters in control groups of most studies. But the researchers also looked at weight gained among those who successfully used a drug to help them quit.
In the main analysis, they found, the untreated quitters gained, on average:
- 1.12 kg (2.46 lbs.) after 1 month
- 2.26 kg (4.97 lbs.) after 2 months
- 2.85 kg (6.27 lbs.) after 3 months
- 4.23 kg (9.3 lbs.) after 6 months
- 4.67 kg (10.27 lbs.) after 12 months
Weight gains among those who quit using pharmacological means were not notably different, the researchers reported.
Using those averages and weighted standard deviations, the researchers found that 16% of the untreated quitters lost weight, 37% gained less than 5 kg (11 lbs.), 34% gained between 5 and 10 kg (11 and 22 lbs.), and 13% gained more than 10 kg.
Aubin and colleagues cautioned that the data were derived from people who went to clinics to be treated for tobacco dependence, so that the findings may not apply directly to those able to quit on their own.
In addition, people who put on large amounts of weight early and resumed smoking because of that would not be included in the dataset, which might affect the findings, they noted.