Association Between Fat-Free Mass and Pulmonary Function in Patients With Cystic Fibrosis: A Narrative Review

The association between body mass index (BMI) and pulmonary function in patients with cystic fibrosis (CF) is well established, yet BMI as the sole indicator of nutrition status fails to assess body composition, specifically fat-free mass (FFM). Reduced FFM is a characteristic of undernutrition and is associated with decreased pulmonary function. A critical review of the literature was undertaken to explore available evidence on the use of FFM derived from dual-energy X-ray absorptiometry (DXA), compared with BMI, to assess pulmonary function and thereby nutrition status in patients with CF. Four cross-sectional studies that met predefined inclusion and exclusion criteria were selected for review. Based on the evidence reviewed, reduced FFM was associated with reduced pulmonary function in both children and adults with CF. FFM was reduced among patients who may not otherwise be identified as at nutrition risk based on BMI alone. FFM, as compared with BMI, appears to be a better indicator of pulmonary function and nutrition status in patients with CF. Although future research is needed to identify and determine FFM measurements that are associated with improved pulmonary function and nutrition status in patients with CF, these findings highlight the potential value and clinical utility of using FFM measurements derived from DXA among patients with CF. Together, FFM and BMI may provide a more comprehensive picture of nutrition status during the nutrition assessment of the patient with CF.