Body fat percentage is independently associated with lower pulmonary function in Korean never-smokers: A cross-sectional analysis of 33,748 adults.

Higher body fat percentage was consistently associated with lower FVC and FEV₁ in both sexes across all BMI categories.

• Study included 33,748 never-smoking adults who underwent spirometry and bioelectrical impedance analysis during health screenings between January 2007 and December 2014.
• Associations were observed across all BMI categories in both men and women (all P < 0.001).
• Participants were stratified by BF% quartiles for analysis.
• Pulmonary function was assessed using pre-bronchodilator spirometry measuring FVC and FEV₁.

After full adjustment, individuals in the lowest BF% quartile demonstrated significantly higher lung function than those in the highest quartile.

• β for FVC: +0.65 L in men and +0.36 L in women (comparing lowest to highest BF% quartile).
• β for FEV₁: +0.46 L in men and +0.28 L in women (comparing lowest to highest BF% quartile).
• All comparisons were statistically significant (all P < 0.05).
• Adjustment included age, BMI, waist circumference, and metabolic factors.

The association between BF% and lower lung function was most pronounced in younger men and in individuals with BMI ≥ 25 kg/m².

• Effect modification by age was observed, with younger men showing stronger associations.
• Effect modification by BMI category was observed, with overweight/obese individuals (BMI ≥ 25 kg/m²) showing more pronounced associations.
• These subgroup analyses suggest BF% provides additional risk stratification beyond BMI alone.

Elevated BF% was independently associated with a markedly increased risk of restrictive ventilatory impairment in both sexes.

• In men, elevated BF% was associated with OR 3.31 (95% CI 2.46–4.47) for restrictive impairment.
• In women, elevated BF% was associated with OR 3.19 (95% CI 2.69–3.79) for restrictive impairment.
• Restrictive and obstructive patterns were defined using lower limit of normal (LLN) criteria.
• Multivariable logistic regression was applied in these sensitivity analyses.

Elevated BF% showed no independent association with obstructive ventilatory patterns.

• In LLN-based analyses, no independent association was observed between BF% and obstructive patterns in either sex.
• This selectivity suggests the mechanism linking adiposity to lung function impairment preferentially affects restriction rather than obstruction.
• The finding contrasts with the strong association observed for restrictive impairment (OR >3 in both sexes).

BMI alone is insufficient to characterize the relationship between obesity and pulmonary function because it cannot distinguish adiposity from lean mass.

• The study evaluated whether BF% is more strongly associated with pulmonary function than BMI.
• BF% was measured using bioelectrical impedance analysis during routine health screenings.
• The authors concluded that BF% offers more refined respiratory risk stratification than BMI in this population.
• Associations between BF% and lung function persisted after adjustment for BMI, waist circumference, and metabolic factors.