Malnutrition in patients with chronic obstructive pulmonary disease (COPD) is classically ascribed to an increased resting energy expenditure (REE) secondary to high cost of breathing. However, malnutrition correlates only weakly with the severity of respiratory dysfunction, which suggests other mechanisms. The aim of the present study was to determine the possible role of diet-induced thermogenesis (DIT). Therefore, we evaluated the relationship between DIT and nutritional status, in particular fat-free mass (FFM) estimated by bioelectrical impedance analysis in 26 patients with stable COPD (mean FEV1 +/- SEM = 36.5 +/- 3.8% of predicted). Ten patients were undernourished (weight < 90% of ideal body weight [IBW] and/or FFM < 69% of IBW), and 16 were normally nourished. Diet-induced thermogenesis was determined by comparing postprandial energy expenditure and REE, the latter being measured after an overnight fast and the former over 4 h after a mixed test meal of 0.4 times REE load. No statistical difference in DIT was found between undernourished and eutrophic patients. There was no relationship between DIT and nutritional or functional parameters, notably FFM. These results suggest that malnutrition is not a consequence of an increased DIT.