The people who quit smoking as part of the study gained an average 2.4 pounds over three months, even though they received support from nicotine patches or the oral medication varenicline (Chantix), which blocks the effect of nicotine on the brain, doctors from Kyoto Medical Center reported in the August issue of PLoS One.
But those smokers with a heavy nicotine addiction experienced three times more weight gain than smokers who were less addicted, the researchers found.
This finding is not unexpected, given that nicotine both suppresses food cravings and increases a person's metabolism, said Dr. Norman Edelman, chief medical officer for the American Lung Association.
"Smoking itself is a weight controller," Edelman said. "The more addicted you are, the more cigarettes you smoke, so you would expect weight gain to happen when you quit."
However, the Kyoto researchers found no significant difference in weight gain between patients who used nicotine patches and those who used varenicline, which does not replace nicotine but instead dulls its effects.
That appears to show there are more factors than nicotine withdrawal at play when ex-smokers gain weight, said Dr. Cheryl Healton, president and CEO of the American Legacy Foundation, an anti-tobacco nonprofit group.
"You would think the group taking nicotine would have lesser weight gain. Instead, it's an underlying personality phenomenon," Healton said. "Some are just more addictive in their personality type, so they satisfied their unmet need with food. They can no longer smoke, and so they eat just a little more a day, which is how you gain weight."
Healton said she sympathizes completely, having quit smoking herself 20 years ago.
"I gained a lot of weight. I didn't care if I ate 12 cupcakes a day, as long as I didn't smoke," she recalled. "I definitely ate food to replace the desire to smoke."
The results suggest that heavily addicted smokers undergoing smoking cessation therapy might need additional behavioral therapy to help prevent weight gain, said study co-author Dr. Koji Hasegawa, director of Kyoto Medical Center's division of translational research.
"Measurement of nicotine dependence is very important before smokers try to quit," Hasegawa said. "Doctors seeing smoking patients, or smokers by themselves, can anticipate whether their body weight will increase or not after they quit smoking. There are effective interventions to reduce the extent of weight gain."
The study focused on 186 people who sought help for smoking cessation at the Kyoto Medical Center's outpatient clinic.
Doctors supplied roughly half with nicotine patches, and the other half with varenicline. They then tracked the patients' weight gain, as well as factors such as depression, cholesterol levels and nicotine addiction that might influence the amount of weight gained while quitting smoking.
"Body weight gain after smoking cessation is a proven syndrome of nicotine withdrawal, as nicotine in the brain facilitates release of dopamine, which suppresses appetite," Hasegawa said.
Nicotine also causes a metabolism boost that helps keep weight off. "You have to eat less when you quit smoking to not gain weight," Healton said. "If you are smoking a pack a day and you stop, but you continue eating the same amount of calories every day, you will gain weight."
However, the person's weight gain tended to be more pronounced if they received a higher score on a standard test for nicotine dependence, implying a more severe addiction to nicotine. In fact, nicotine dependence proved the most significant factor related to weight gain.
Healton noted that the average couple of pounds gained by the study participants is less than the usual weight gain experienced by smokers who are quitting. Men tend to gain about 6 pounds and women tend to gain about 8 pounds.
"As weight gain goes, this isn't much," she said. "This shows if people are receiving nicotine therapy, they should continue to have appetite suppression."
Both Hasegawa and Healton said it might be more beneficial for smokers to not worry about gaining weight and instead focus on successfully quitting tobacco.
"It raises the problem of trying to address two behavioral problems at the same time, depriving yourself of smoking and of food," Healton said. "There's nothing that will improve your life expectancy more than quitting smoking, and we know that at some point in time, usually a year out, smokers who quit are able to lose the weight they've gained."
For more about smoking cessation, visit the U.S. Centers for Disease Control and Prevention.