|Researchers are gaining a clearer
understanding of why some smokers may be at particular risk for weight gain after they
Smoking increases the body's use of
energy, and the effect is greater when smokers are physically active than when at rest.
That means that smokers who are trying to quit not only need to keep tabs on what they
eat, but they also may need to increase their activity levels significantly to burn
calories previously taken care of by smoking.
"The majority of the weight gained after smoking
cessation is accounted for by increased food consumption, but approximately 30 percent is
left unaccounted for," said Peter P. Rowell, PhD, one of the authors of the study.
"Individuals who tend to smoke while moving around during the day, rather than while
watching TV in the evening, experience greater smoking-related energy expenditure and may
be at greater risk for post-cessation weight gain."
The researchers measured the energy consumption of 10 male
smokers as they rested or pedaled a stationary bicycle, either while smoking two
cigarettes or not. They took readings of the men's heart rate and blood pressure and
analyzed their blood levels of nicotine and several stress hormones. The men pedaled at a
pace designed to approximate a light level of physical activity equivalent to a
slow walk or moving about the house or work.
Rowell and his colleagues from the University of Louisville
and Florida State University, Tallahassee, report their findings in the current issue of Nicotine
& Tobacco Research.
Smoking while active led to significantly greater increases
in energy consumption than did smoking while resting, the researchers found. Smoking
increased energy consumption by 6.3 percent when the men were physically active, but by
just 3.6 percent when they remained at rest.
Smoking while physically active also led to greater
increases in blood levels of nicotine and greater increases in the stress hormones
epinephrine and norepinephrine compared with smoking at rest. Interestingly, cigarette
smoking produced greater changes in heart rate than did the light physical activity, the
When the researchers controlled for blood levels of
nicotine, they found that the difference in the increase in energy consumption between
smoking while active and smoking at rest was no longer significant. That result suggests
that increases in nicotine levels during physical activity are responsible for the
increase in energy consumption observed, they say.
"It is unclear whether increased nicotine during
physical activity is related to a change in smoking pattern taking deeper or more
frequent puffs or shifting blood away from the liver where nicotine is
metabolized," Rowell says.
This research was supported by a grant from the Kentucky
affiliate of the American Lung Association.
Nicotine & Tobacco Research is the official
peer-reviewed quarterly journal of the Society for Research on Nicotine and Tobacco. For
information about the journal, contact Gary E. Swan, PhD, at (650) 859-5322.