The effect of smoking two cigarettes on resting metabolic rate with and without food

Resting metabolic rate (RMR) was measured using a ventilated hood apparatus in 15 subjects before (BMR) and for 5 h after (5HEE) four treatments. In 10 smokers (five occasional and five habitual) the treatments were: food (600 kcal (2.51 MJ) breakfast) with and without smoking two cigarettes (F +/- S) and no food with and without smoking (NF +/- S). In five non-smokers duplicate measurements of food (F-S) and no food (NF-S) were made. In non-smokers the thermic effect of food (TEF) averaged 9.35 per cent of the ingested energy. Duplicate measures of 5HEE showed good reproducibility both with and without food (c.v. 2.5 and 1.3 per cent respectively). In smokers, RMR did not increase after smoking even during the first 15-30 min. There were no apparent differences in response between occasional and habitual smokers. 5HEE and delta 5HEE (5HEE minus BMR) were significantly lower after food with smoking than without smoking (-16 kcal (67 kJ)/5 h, P less than 0.001 and -14 kcal (59 kJ)/5 h, P less than 0.02 respectively) but not significantly lower after smoking without food. TEF was lower with smoking (8.6 per cent of ingested energy) than without smoking (10.0 per cent of ingested energy) but the difference was not significant (P = 0.23). TEF in smokers regardless of treatment averaged 9.3 per cent of the ingested energy. We conclude that any effects of smoking two cigarettes in isolation after overnight deprivation are too small or too variable to consistently influence RMR or the thermic effect of food.