• Saba Sheikh, Babette S Zemel, Virginia A Stallings, Ronald C Rubenstein, and Andrea Kelly.
• Division of Pulmonary Medicine, Cystic Fibrosis Center, Perelman School of Medicine at the University of Pennsylvania , Philadelphia, PA , USA ; Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania , Philadelphia, PA , USA.
• Front Pediatr. 2014 Jan 1; 2: 33.

BackgroundLower body mass index (BMI) is associated with worse pulmonary function in cystic fibrosis (CF).Hypothesislean body mass (LBM) is more strongly associated with pulmonary function than BMI is.MethodsAnthropometrics, body composition by dual x-ray absorptiometry, and pulmonary function were determined in pancreatic insufficient CF (PI-CF) youth. Sex and age-adjusted Z-scores (BMI-Z, LBMI-Z, FMI-Z) were generated for CF and controls. (1) Associations of BMI-Z with LBMI-Z and FMI-Z and (2) age-adjusted associations of BMI-Z, LBMI-Z, and FMI-Z with FEV1%-predicted were tested.ResultsTwo hundred eight PI-CF subjects had lower BMI-Z, LBMI-Z, and FMI-Z compared to 390 controls. BMI-Z was associated with lower LBMI-Z (p < 0.0001) in PI-CF. In females, LBMI-Z and BMI-Z were positively associated with FEV1%-predicted; this relationship did not persist for FMI-Z after adjustment for LBMI-Z. In males, only LBMI-Z and BMI-Z were associated with FEV1%-predicted.ConclusionIn PI-CF youth, deficits in LBM were apparent. At lower BMI percentiles, BMI may not accurately depict LBM in PI-CF. In under-nourished PI-CF youth, this preservation of FM in preference to LBM is relevant since LBMI-Z, but not FMI-Z, is positively associated with FEV1%-predicted. Lean body mass index is more strongly associated with lung function compared to BMI, especially in the under-nourished child and adolescent with PI-CF.

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