The relationship between dietary fiber intake and lung function in the national health and nutrition examination surveys

Rationale: Extensive research supports a protective effect of a high-fiber diet in certain disease states; however, little is known about its relationship to lung health. The National Health and Nutrition Examination Surveys (NHANES) contain spirometry measures and dietary intake information, allowing us to assess this relationship. Objective: Determine the association between fiber intake and measures of lung function in a representative sample of U.S. adults. Methods: Participants included 1,921 adults who had spirometry measurements and fiber intake available. The primary outcomes were lung function measurements, including FEV₁, FVC, and percent predicted FEV₁ and FVC. We also conducted a categorical analysis of fiber intake and airflow restriction and obstruction based on Global Initiative for Chronic Obstructive Lung Disease and Spirometry Grade (SG) classifications. Multivariable regression models were used to look at the association of lung function measurements with dietary fiber intake after adjustment for relevant confounders. All analyses accounted for the weighted data and complex design of the NHANES sample. Measurements and Main Results: Subjects in the highest quartile intake of fiber had mean FEV₁ and FVC measurements that were 82 ml and 129 ml higher than the lowest quartile of intake (P = 0.05 and 0.01, respectively), and mean percent predicted FEV₁ and FVC values that were 2.4 and 2.8 percentage points higher (P = 0.07 and 0.02, respectively). In the categorical analysis, higher fiber intake was associated with a higher percentage of those with normal lung function (P = 0.001) and a significant decline in the proportion of participants with airflow restriction (P = 0.001). Conclusion: Low fiber intake was associated with reduced measures of lung function. A diet rich in fiber-containing foods may play a role in improving lung health.