Cigarette smoking and the thermic responses to isocaloric meals of varying composition and palatability.

The 4-h thermic responses to glucose and a liquid formula meal (Study 1), and to a solid food 'breakfast' meal and the liquid formula meal (Study 2) were measured in a group of young weight-stable female subjects. The groups recruited for the two studies consisted of nine smokers and seven non-smokers (Study 1) and six smokers and eight non-smokers (Study 2). The habitual smokers presented after a 12-h abstention from cigarettes but were permitted to smoke following the meal; their thermic responses were thus due to the combined thermogenic effects of smoking and feeding. The mean thermic responses to all three types of meal were greater for the smokers than for the non-smokers, and the magnitude of this difference was similar irrespective of the type of meal given (range 52 kJ-70 kJ). The thermic responses to the liquid formula meal tended to be greater than those to an isocaloric glucose load for smokers and non-smokers (Study 1). In Study 2, the increase in energy expenditure occurring during the first hour following the 'breakfast' meal was consistently greater than the 1-h response to the liquid formula meal. The larger thermic response to feeding to all three meal-types observed in the groups of smokers when compared with non-smokers, is attributed to the actions of cigarettes smoked (mean 4.6) during the period of measurement. It is concluded that whilst the thermic response to feeding is augmented in cigarette smokers this increase is an additive effect and is independent of the size and nature of the thermic effect of the meal.