Elucidating the Relationship Between Body Fat Index and Pulmonary Health: Insights from Cross-Sectional Analysis and Mendelian Randomization.

Objective: To evaluate the relationship between body fat index and pulmonary health.

Methods: In the multiethnic population-based cross-sectional study, a multivariable linear regression model was adapted to assess the association of fat mass/percentage with forced expiratory volume in 1 second (FEV₁)/forced vital capacity (FVC). The Mendelian Randomization (MR) method was used to assess the causal associations of fat mass/percentage in specific body parts with FEV₁ and COPD risk. Sensitivity analysis of MR was performed to assess the robustness of estimates.

Results: In the cross-sectional analysis, a non-linear relationship was observed between fat mass and FEV₁ without adjustment. After multivariate adjustment, the negative associations of fat mass/percentage with FEV₁/FVC were found. In the MR study, genetically determined fat presented a negative causal effect on FEV₁ (e.g., estimate = -0.170, P < 0.001 for left leg fat mass). The causal associations of genetically determined body fat with clinical diagnosis COPD were also determined (e.g., OR = 1.936, P < 0.001 per 1.9 kilograms increase in left leg fat mass).

Conclusion: We present strong evidence on the causal relationship between body fat mass/percentage and both the deterioration of lung function and the increased risk of COPD. Additional efforts are required to mitigate the negative effects of body fat.