Increased 24-hour energy expenditure in cigarette smokers.

Abstract We studied the effect of smoking on energy expenditure in eight healthy cigarette smokers who spent 24 hours in a metabolic chamber on two occasions, once without smoking and once while smoking 24 cigarettes per day. Diet and physical exercise (30 minutes of treadmill walking) were standardized on both occasions. Physical activity in the chamber was measured by use of a radar system. Smoking caused an increase in total 24-hour energy expenditure (from a mean value [±SEM] of 2230±115 to 2445±120 kcal per 24 hours; P<0.001), although no changes were observed in physical activity or mean basal metabolic rate (1545±80 vs. 1570±70 kcal per 24 hours). During the smoking period, the mean diurnal urinary excretion of norepinephrine (±SEM) increased from 1.25±0.14 to 1.82±0.28 μg per hour (P<0.025), and mean nocturnal excretion increased from 0.73±0.07 to 0.91±0.08 μg per hour (P<0.001). These short-term observations demonstrate that cigarette smoking increases 24-hour energy expenditure by approximately ...