Fiber
Andrianasolo et al. 44 studied multiple types of dietary fiber intake in association with reported asthma control (assessed at 6 months longitudinal intervals) as indicated by the Asthma Symptom Score and the Asthma Control Test score. They noted that higher quintiles of dietary fiber intake (total, soluble, insoluble fibers from cereals, fruit and seeds) was associated with lower Asthma Symptom Score (0.73, 95 % CI 0.67-0.79 in women; and 0.63, 95 % CI 0.55-0.73 in men, both p<0.001) compared to participants in the lowest quintile of total dietary fiber intake, indicating that higher fiber intake was associated with fewer reported asthma symptoms. Higher total fiber intake, mostly insoluble fiber and fiber from cereals was also associated with lower odds of an ACT score indicating impairment (OR 0.72, 0.55-0.95, p=0.01 for women, OR 0.45, 0.26-0.79, p=0.01 for men). Bseikri et al.45 noted no overall association between consumption of a high fiber nutritional supplement bar (CHORI-bar) and pulmonary function testing, ACT score and PedsQoL Am score, although they did note that among treatment-compliant subjects with non-eosinophilic asthma, 8 weeks of CHORI-bar consumption was associated with increased FVC, FEV-1, and FEF-25-75. McLoughlin at al.46 noted that a 7 day trial of inulin (12g per day) supplementation was associated with improved Asthma Control Questionnaire score exceeding the minimal important difference, though not associated with objective parameters of improved lung function, but they noted a subgroup effect among those with the poorest asthma control in that the inulin supplementation was associated with decreased eosinophilic airway inflammation, and better overall control among those with eosinophilic vs. non-eosinophilic asthma. Saeed et al. 47noted an association between low dietary fiber intake and increased odds of reported asthma among US respondents on the NHANES survey. They noted increased odds of asthma with lower fiber intake (lowest vs. highest reported quartile, OR, 1.4; 95% CI 1.0– 1.8; P = 0.027) with significant interactions between fiber and both sex and race/ethnicity, in particular among women and non-Hispanic white adults. Lowest quartile fiber intake was associated with increased odds of reported wheeze (OR, 1.3; 95% CI, 1.0–1.6; P = 0.018) and cough (OR, 1.7; 95% CI, 1.2–2.3; P = 0.002).
Two Australian studies looked at the effects of fiber during pregnancy. Grieger et al.48 noted that, after adjusting for total energy intake, pregnant women with uncontrolled asthma had higher intakes of fiber (OR 1.07, 1.03-1.13, p=0.003). Pretorius et al.49 noted that higher reported maternal dietary intake of resistant starch was associated with reduced odds of doctor diagnosed wheezing in the infant (aOR 0.68 (95% CI 0.49-0.95, p = 0.02).