Optimal nutritional support is considered to be an integral part in the management of cystic fibrosis (CF). Several factors contribute to increased resting energy expenditure (REE), which itself can lead to energy imbalance and thus contribute to deterioration of the nutritional status. We aimed to assess the impact of lung parenchyma damage on REE and correlated these findings with forced expiratory volume in 1 s (FEV(1)). Twenty patients performed respiratory function testing (FEV(1)), pulmonary high-resolution computed tomography (HRCT) and assessment of REE with open circuit indirect calorimetry. HRCT was scored by using a modified Bhalla method. Mean HRCT score was 8.4 and mean REE value was 108.4% predicted vs. 96.5% predicted of 16 healthy subjects (P<0.01). There was a significant correlation between HRCT score and REE (P<0.01), HRCT score and FEV(1) (P<0.001) and REE and FEV(1) (P<0.05). The correlations demonstrate a close correlation between lung damage and elevated REE in people with CF. Prevention of negative energy balance is an important part in follow-up of patients with CF. Any increase in REE should raise suspicion of progress in lung impairment.