Sex specific cross sectional reference values for the lung function indices usually employ a linear model with a term for age and height. The purpose of this study was to determine the effects of the body mass index (BMI), the fat percentage of the body mass and the fat-free mass index (FFMI) on the forced expiratory volume curve.

Between January 2000 and December 2001, a total of 300 subjects, 150 men and 150 women (mean age : 45±13 years), with a normal lung function were enrolled in the study sample. This study measured the FEV₁, FVC and FEF_25-75% from the forced expiratory volume curve by a spirometer and the body composition by a bioelectrical impedance method in all subjects. Multiple regression analysis was used in order to examine the effects of the body composition on the parameters derived from the forced expiratory volume curve.

After adjusting for age, the BMI and Fat percentage improved the descriptions of the FVC (p<0.05, r²=0.491) and FEV₁ (p<0.05, r²=0.654) in women. In contrast, the FFMI contributed significantly to the FVC (p<0.05, r²=0.432) and FEV₁ (p<0.05, r²=0.567) in men. The FEF_25-75% correlated with the fat percentage in women (p<0.05, r²=0.337).

These results suggest that the BMI, the fat percentage and the FFMI are significant determinants of the forced expiratory volume curve. The pulmonary function test, when considering the BMI, the fat percentage and the FFMI, might be useful in clinical applications.