The Effect of Nicotine on Energy Expenditure during Light Physical Activity

The metabolic effects of nicotine have been implicated in the relation between smoking and lower body weight. This study examined whether the nicotine-induced increase in the metabolic rate observed at rest is also present during physical activity. We compared the energy expenditure of 10 male smokers receiving nicotine (15 μg per kilogram of body weight) with that of 10 male smokers receiving placebo on two occasions, each including a period of rest and a period of exercise on a modified bicycle ergometer at workloads designed to simulate and standardize light daily activity. All had abstained from cigarette smoking the night before the study. The excess energy expenditure attributable to nicotine was more than twice as great during exercise (difference between groups, 0.51 kJ per kilogram per hour, or 12.1 percent of the metabolic rate at rest; P<0.001) than during rest (0.23 kJ per kilogram per hour, or 5.3 percent of the metabolic rate at rest; P<0.05). In contrast, the expenditure was not affected by placebo during exercise or rest in the smokers or in a comparison group of 10 nonsmokers, indicating that smoking status has no long-term metabolic effect in the absence of short-term nicotine intake. We conclude that the relatively small metabolic effect of nicotine when the subject is at rest is enhanced during light exercise. Our data also suggest that the weight gain that often follows smoking cessation may be influenced not only by nicotine intake but also by the level of physical activity a smoker typically engages in while smoking. EPIDEMIOLOGIC research shows a consistent inverse relation between cigarette smoking and body weight. Smokers weigh less than nonsmokers¹ and gain weight after they stop smoking.^{2 3 4} Weight gain after smoking cessation is frequently cited as a factor leading to relapse.⁵ The exact cause of the relation between smoking and body weight remains unknown, but evidence suggests that it cannot be adequately explained by differences between smokers and nonsmokers or exsmokers in caloric intake^1,3,6 or energy expended during physical activity.^1,3,4,7 The failure to document such differences has increased speculation that smoking may affect the energy balance by increasing the metabolic rate⁵ —…