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Let's be honest: quitting smoking usually does make you fatter
There's no use in sugar-coating the truth: Nicotine is an appetite suppressant, and smoking prevents weight gain. Not wanting to gain weight is a common reason why body-obsessed teenage girls say they smoke--and as far as we know, they're "right:" teens who smoke gain slightly less weight than teens who don't.
It's also long been believed that quitting smoking causes weight gain in most people--for example, ex-smokers weigh more, on average, than smokers or never-smokers--but no one had ever really quantified how much. Now, thanks to Henri-Jean Aubin, Amanda Farley, Paul Aveyard et al, we have a pretty good idea: on average, people who quit smoking will gain 10 pounds at one year. However, results may vary: one in six people who quit smoking lost weight at one year, and one in eight gained more than 22 pounds. The authors published their meta-analysis in the July 10, 2012 BMJ.
What They Did
The investigators performed a meta-analysis on 62 studies on smoking cessation that reported weight gain. All patients were motivated to quit, in that they had presented for treatment in smoking cessation clinics or for that purpose with their physician. Studies were reported as being of high-quality overall.
What They Found
In all groups (smokers quitting with or without pharmacologic assistance), patients gained weight at an average of 2.2 pounds (1 kg) per month for the first three months (~6 pounds, 3 kg). Weight gain then slowed slightly, to reach an average of ~10 pounds (4-5 kg) at one year. As would be expected, there was a wide variability of weight change:
16-21% of patients (one in five or six) lost weight throughout the study.
About one-third (35-38%) gained less than 10 pounds (5 kg).
About one-third (29-34%) gained more than 10 pounds (5 kg) but less than 22 pounds (10 kg).
13-14% of patients (about one in seven) gained more than 22 pounds (10 kg) at 12 months.
People using pharmacologic smoking cessation therapies like Zyban (bupropion), Chantix (varenicline) or nicotine replacement therapy had an equal amount of weight gain--smoking cessation treatment did not reduce the weight gained in the first year after quitting smoking.
What It Means
The previous best study, which is 20 years old and flawed, suggested 6 pounds was the "average" weight gain after quitting smoking. That number has made it into lots of pamphlets and counseling sessions, but this better and more recent study suggests it's wrong.
The nice thing about not having firm evidence surrounding a clinical issue is, you can put a positive "spin" on the situation while being ethical, i.e., not lying. For example, if a patient asked "Will I gain weight if I quit smoking?" it was perfectly acceptable (in my opinion) to say "No, not necessarily!" But the truth is, I had no idea.
Now, I would say that counsel would be dishonest. It's still possible to offer the optimistic "Some people lose weight after quitting smoking" -- but as I write that, it sounds kind of lame and disingenuous.
It's unfortunate that weight gain appears so inseparable from smoking cessation. This is especially true with regard to women who smoke, because they may be especially discouraged from quitting by the weight gain predicted by this study. In surveys at the U. of Michigan, more than half of women under age 25 who smoked were unwilling to try to quit if it meant they would gain any weight at all. Even among women over 40, almost 40% said they would not quit if it meant they would gain even a pound or two. Among all women, 75% said they would rather keep smoking than gain more than 5 pounds after quitting. Men were more accepting of a hypothesized 10-pound weight gain after quitting. (These were not motivated quitters, who might be more open to the possibility of weight gain after smoking cessation.)
It should go without saying that even a 20-pound weight gain is less harmful to health than continued smoking. But it's not you I have to convince!
Aubin H-J et al. Weight gain in smokers after quitting cigarettes: meta-analysis. BMJ 2012; 345: e4439 (July 10, 2012.)