Energy Expenditure and Substrate Oxidation in Clinically‐Stable Adults with Cystic Fibrosis
Authors: Pintas Stephanie K. , Ivie Elizabeth A. , Millson Erin C. , Tran Phong , Stecenko Arlene A. , Ziegler Thomas R. , Alvarez Jessica A. 
Published: November 2023

OBJECTIVEUndernutrition is common in patients with cystic fibrosis (CF); however, the majority of studies have focused on pediatric CF populations. The aim of this study was to examine resting energy expenditure (REE) and substrate oxidation rates of clinically stable adults with CF compared to healthy controls (HC). Based on the literature that REE is elevated and fat oxidation rates are lower in CF children, we hypothesized that REE would be higher and whole‐body fat oxidation would be lower in adults with CF versus HC.PATIENTS AND METHODSWe studied 16 clinically‐stable adults with CF and 17 healthy subjects matched to CF subjects for age, body mass index (BMI), sex and race. REE was determined by indirect calorimetry (IC) and also estimated with the Harris‐Benedict prediction equation in the fasted state. Carbohydrate and fat oxidation rates were assessed using several published stoichiometric equations. Lean body mass was measured using dual‐energy X‐ray absorptiometry. Wilcoxon signed‐rank tests were used for statistical comparisons.RESULTSAdults with CF and HC did not differ significantly in age (28.3 vs 28.1 yrs, respectively, p=0.95), gender (44% vs 71% female, p=0.17), race (87.5% vs. 76.5% Caucasian, p=0.99), or BMI (21.1 vs 21.7 kg/m2, p=0.54). Among CF subjects, 63% were homozygous for the ΔF508 mutation and the mean percent predicted forced expiratory volume in 1 second was 70%. The CF and HC did not differ significantly in lean body mass (43.6 vs 44.0 kg, p=0.96), fat mass (14.4 vs 16.2 kg, p=0.38), or percent body fat (23.6 vs 25.9%, p=0.42). VO2 (0.21 vs 0.19 L/min, p=0.19), VCO2 (0.18 vs 0.16 L/min, p=0.16), the respiratory quotient (0.86 vs 0.86, p=0.83), and absolute REE did not differ between groups (CF: 1429 kcal/day, HC: 1358 kcal/day, respectively; p=0.17). However, the REE/kg of body weight was higher in CF versus HC subjects (24.8 vs 21.8 kcal/kg; p=0.01). REE/kg of lean body mass (LBM) tended to be higher in patients with CF (34.1 vs 31.2 kcal/kg LBM; p=0.06). Similarly, measured REE as a percentage of predicted REE by the Harris‐Benedict prediction equation (% predicted REE) tended to be higher in CF vs HC (98 vs 91%, p=0.06). Regardless of methods used, there was not a significant difference between fat oxidation or carbohydrate oxidation rates (all p>0.05).CONCLUSIONSREE, particularly as a function of kg body weight, was higher in adults with CF compared to HC well‐matched for age, BMI, sex and race. This likely reflects the higher metabolic demands associated with lung infection and inflammation in subjects with CF. The Harris Benedict prediction equation more accurately predicted measured REE in CF subjects compared to HC. There was no significant difference between fat or carbohydrate oxidation rates between CF and HC subjects. Further study with larger sample sizes are required to determine potential differences between adults with CF and HC, the relationship to lung dysfunction, and the nutritional implications of these findings.Support or Funding InformationSupported by the National Institutes of Health Award Numbers K01 DK102851 (JAA), K24 DK096574 (TRZ) and UL1TR000454