Association of Dietary Fiber on Asthma, Respiratory Symptoms, and Inflammation in the Adult National Health and Nutrition Examination Survey Population

Rationale: High intake of dietary fiber may have antiinflammatory properties and be protective against respiratory morbidity. Objectives: We examined the relationship between dietary fiber intake and asthma, respiratory symptoms, and inflammation among adults who participated in the 2007 to 2012 NHANES (National Health and Nutrition Examination Survey). Methods: We analyzed data from adults 20 to 79 years of age (n = 13,147) with complete information on fiber intake, total calorie intake, body mass index, smoking status, and poverty level. Fiber intake was categorized into quartiles, with Q1 being lowest quartile of intake and Q4 being the highest quartile. Respiratory morbidities included asthma, wheeze, cough, and phlegm. Self-report questionnaires were used to define asthma, wheeze, cough, and phlegm production. Serum C-reactive protein (CRP) was used as a biomarker of inflammation. Exclusion criteria included current pregnancy and implausible intake of total calories. Results: A total of 69.5% of participants were non-Hispanic white; 54.5% were nonsmokers, and 7.8% had current asthma. After adjusting for covariates, fiber intake was associated with asthma (P =0.01), with an increased odds of asthma with lower fiber intake (Q1 vs. Q4: odds ratio [OR], 1.4; 95% confidence interval [CI], 1.01.8; P = 0.027). There were significant interactions between fiber and sex and fiber and race/ethnicity; stronger associations were seen for women and for non-Hispanic white adults. Low fiber intake (Q1) was associated with increased odds of wheeze (OR, 1.3; 95% CI, 1.01.6; P= 0.018), cough (OR, 1.7; 95% CI, 1.2-2.3; P= 0.002), and phlegm (OR, 1.4; 95% CI, 1.1-2.0; P = 0.021) compared with high fiber intake. The odds of having high CRP versus nondetectable CRP were 1.6 times higher in the low-fiber group (Q1) compared with high-fiber group (Q4; OR, 1.6; 95% CI, 1.0-2.5). Conclusions: High-fiber diet may mediate an inflammatory response and decrease odds of having asthma, especially for women and specific racial groups, cough, wheeze, and phlegm production when compared with low-fiber diet.