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 researchers say.

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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.