Physical activity and liver disease affect the fat-free mass in adolescents with cystic fibrosis

Cystic fibrosis (CF) is predominantly a lung disease but is also characterised by impaired skeletal muscularity and a reduction in fat-free mass. We aimed to test the hypothesis that clinical and anthropometric parameters would determine fat-free mass impairment in adolescents with CF. We measured the fat-free mass index (FFMI) using bioelectrical impedance, the lung function using spirometry, the number of shuttles as a measure of exercise tolerance and the reported physical activity in children and young people with CF in a tertiary centre at King’s College Hospital, London, UK. CF-related liver disease was diagnosed by abnormal liver enzymes and/or ultrasonography. We studied 28 children and young people (11 male) with a median (interquartile range (IQR)) age of 15 (13–17) years. They had a median (IQR) FFMI of 13.5 (11.6–15.1) kg/m(2). The FFMI significantly correlated with age (rho = 0.568, p = 0.002), number of shuttles (rho = 0.691, p < 0.001) and reported hours of activity per day (rho = 0.426, p = 0.024). The median (IQR) FFMI was significantly higher in male [15.1 (13.1–18.6) kg/m(2)] compared to female participants [12.7 (11.6–14.1) kg/m(2), p = 0.008]. The median (IQR) FFMI was significantly lower in the 10 (36%) participants with liver disease [11.9 (11.5–13.4) kg/m(2)] compared to the FFMI in the remaining 18 participants without liver disease [14.4 (12.5–15.9) kg/m(2), p = 0.027]. Conclusion: Fat-free mass increases with increasing age and growth in adolescents with CF. Physical activity exerts a beneficial effect on fat-free mass, and CF-related liver disease negatively affects fat-free mass in adolescents with CF.