Any smoker who's tried to kick the habit has probably experienced it: Extra pounds pile on within the first few weeks after quitting. It's still unclear exactly how smoking affects body weight, but new research finds that the culprit is not leptin, a protein implicated in weight control.
Leptin levels are not significantly related to a person's smoking status, according to the study by Kenneth A. Perkins, Ph.D., and Carolyn Fonte, R.N., of the University of Pittsburgh School of Medicine. The researchers compared leptin levels between groups of male and female smokers, nonsmokers and ex-smokers, as well as a smaller set of the smoking group that quit for at least three weeks.
The study results are published in the December issue of the journal of Nicotine & Tobacco Research.
Leptin helps manage body weight by reducing food uptake and increasing energy expenditure. Some researchers have suggested that smoking may abnormally boost leptin levels, and could be part of the reason why smokers tend to have lower body weights and experience weight gain when they give up cigarettes.
Despite numerous studies of leptin and smoking, evidence for a link has been mixed, possibly because previous research looked at the phenomenon in narrowly defined age or ethnic groups, according to Perkins and Fonte.
"To our knowledge, this is the first study to compare leptin levels in long-time, nicotine-free ex-smokers with those of smokers or nonsmokers," say the authors.
Perkins and Fonte measured leptin in 77 young and middle-aged men and women with a range of smoking and nonsmoking histories. They also tracked the participants' body mass index and alcohol and caffeine intake, since each of these factors is associated with leptin levels in the body.
After accounting for the influence of body mass, the researchers found no significant difference between nonsmokers, ex-smokers and current smokers. The effects of caffeine and alcohol weren't significant except in the case of alcohol for women, where more alcohol consumption lowered leptin levels.
As expected, both women and men who stopped smoking for three weeks gained an average of four pounds. Instead of seeing a drop in leptin levels among these newly abstinent smokers, however, the researchers observed a significant rise in leptin levels among the women in the group. Leptin levels did not change in the men.
"This is the opposite of what would be expected if leptin were responsible for this cessation-induced weight gain," Perkins notes.
Despite finding no link between smoking and leptin levels, the researchers suggest that smoking may influence other unknown factors, including hormones, which regulate eating and energy expenditure and affect body weight as a result.
This study was supported by grants from the National Institute on Drug Abuse.
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