Metabolic effects of nicotine after consumption of a meal in smokers and nonsmokers
It is generally believed that cigarette smokers are thinner than nonsmokers, and that they gain weight when they quit smoking; research studies have supported these two theories. But researchers have not found that smokers engage in more physical activity or eat less than nonsmokers. Instead it appears that smoking, and specifically the nicotine in cigarette smoke, raises the metabolic rate so that more energy is consumed in maintaining basic body functions. One study reported that nicotine raised the metabolic rate slightly when subjects were at rest, but the effect was too small to explain the difference in energy metabolism observed between smokers and nonsmokers. This study was performed to investigate whether nicotine has a larger influence on metabolic rate after a meal, which is a time when many smokers tend to smoke. Twenty healthy young men were studied; half were smokers and half did not smoke. Each subject was evaluated four times. In one session subjects drank a high-calorie beverage followed by a nicotine nasal spray, administered every 20 minutes for the two hours after the meal. In the other three sessions they drank the high-calorie beverage followed by a placebo (inert) nasal spray, water followed by the nicotine spray, and water followed by the placebo spray. Both the nicotine alone (after water consumption) and the calorie consumption alone (followed by placebo) raised the metabolic rate, as expected. But the addition of nicotine treatment after the high-calorie drink did not significantly raise the metabolic rate over the level produced by the calories alone. Thus the theory that smoking after a meal would further raise the metabolic rate was not supported by this study. Also, there was no difference between smokers and nonsmokers in their responses to either the meal or the nicotine nasal spray. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: American Journal of Clinical Nutrition
Acute effects of nicotine on resting metabolic rate in cigarette smokers
Research has shown that cigarette smokers weigh less than nonsmokers on average, and that smokers tend to gain weight after they quit smoking. The difference in body weight does not appear to be due to either caloric intake or exercise; smokers and nonsmokers do not differ on these factors. Instead it seems that smoking speeds up the metabolism so that more calories are burned. Specifically, smoking appears to increase the resting metabolic rate (RMR), which is the portion of total metabolic rate that fuels basic bodily functions such as breathing and heart function. Minor increases in RMR can reduce body weight significantly over time because RMR accounts for approximately 70 percent of total calories burned. Based on animal research, the substance in cigarette smoke thought to affect RMR is nicotine. This study examined the effect of nicotine alone on RMR in 18 adult male smokers, aged 18 to 30. To isolate the influence of nicotine from the 4,000 other substances in tobacco smoke, the men inhaled a nicotine nasal spray. This also allowed delivery of precise doses of nicotine which would be impossible if individuals smoked cigarettes in their usual manner; the amount of smoke inhaled and cigarette brands vary greatly among smokers. The results showed that inhalation of nicotine spray increased RMR significantly, by six percent over baseline. Use of placebo nasal spray without nicotine raised RMR by three percent over baseline, and this increase was attributed to energy used in inhalation. The difference between nicotine and placebo sprays was also significant. The authors note that the doses of nicotine delivered were equivalent to or less than an average cigarette so that the results would be relevant to smokers who use low-nicotine brands.
Publication Name: American Journal of Clinical Nutrition
The effect of nicotine on energy expenditure during light physical activity
The effects of nicotine on the metabolism have been implicated in the relationship between lower body weight and smoking. This study examines whether this effect, which has been observed at rest, is present during physical activity. The energy expenditures of ten male smokers receiving nicotine were compared to a similar group which did not receive nicotine. All participants abstained from smoking cigarettes the night before the study. The patients were tested on a modified stationary bicycle (ergometer) at levels of work designed to simulate light daily activity. The investigators report that excess energy expenditure attributable to nicotine was more than twice as great during exercise than during rest. This effect was not found in the male smokers who did not receive nicotine. The authors conclude that the relatively small metabolic effect of nicotine at rest is dramatically enhanced during light exercise. These data suggest that the weight gain that often follows quitting smoking may be influenced not only by nicotine intake, but also by the level of activity a smoker generally engages in while smoking.
Publication Name: The New England Journal of Medicine
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