Does quitting smoking really make you gain weight?

If your New Year's resolution is to quit smoking, conventional wisdom says you'll probably put on five or 10 pounds.

If you're also pondering a New Year's resolution to lose weight, it might be tough to give up cigarettes if you fear you'll pack on some pounds because of it.

University of Michigan researcher Dan Eisenberg is beginning a study to look at the real cause and effect between quitting smoking and gaining weight.

Eisenberg, assistant professor of health management and policy at the U-M School of Public Health, isn't ruling out a connection between weight and smoking. Smoking works as an appetite suppressant, and there is significant literature showing a relationship between quitting smoking and gaining weight.

"There hasn't been a really valid estimate of what the connection is," Eisenberg said. "I am trying to find out scientifically what the relationship is."

Part of the challenge in understanding the relationship is that smokers can either choose to continue smoking or to quit, creating what's called a selection bias—people sort themselves into one group or the other, and that could create some of the effect.

Eisenberg said it is possible that those who quit are more health conscious or more disciplined, and perhaps because of that, they control their eating better. The true effect of quitting smoking, physiologically, might be something more like a gain of 20 pounds—but the quitters reign it in.

On the flip side, because there is a general belief that quitting smoking causes weight gain, perhaps people who are not worried about gaining weight are more likely to quit smoking. That might mean quitting smoking should only cause a gain of five pounds, but since the quitters aren't all that worried, they pack on 10 or more instead.

Eisenberg hopes to untangle some of the question by inviting smokers to participate in a study in which some will randomly be assigned to a smoking cessation program and others will not.

Because the study will help choose who gets help quitting, some selection bias should be overcome, Eisenberg said. But even with help, not everyone will quit, so he will look at differences in the probability of quitting.

Eisenberg received a grant of about $18,000 from the University of Michigan Tobacco Research Network to help fund his pilot research study.

Eisenberg expects to have some early results from the study by summer 2005.