High intake of dietary fiber linked to reduced risk of asthma, finds study

The findings have been published in the Annals of the American Thoracic Society.

Asthma is a chronic inflammatory disease of the airways, affecting approximately 339 million people globally. This rising burden of asthma has followed in parallel dramatic shifts of dietary habits towards a "Western" diet (high in processed refined foods, high in sugars and fats, and low in anti-oxidant and fiber levels) and away from a "Prudent" diet (high in fruits, vegetables, whole grains, lean meat, fish, antioxidants and fiber and low in fat and dairy products).

An important difference between a "Western" and "Prudent" diet is the level of dietary fiber. The beneficial effects of a diet rich in fiber include improved gut health, reduced risk of obesity, cardiovascular disease, coronary heart disease, cancer, stroke, type-2 diabetes, and mortality due to cancer, heart and respiratory diseases. A proposed mechanism to explain the anti-inflammatory effect of fiber is the increased production of circulating short-chain fatty acids (SCFAs), e.g. acetate, propionate, and butyrate, which form after fermentation of fiber by gut microbiota.

Though several studies have looked at the association between dietary patterns with asthma incidence or symptoms yet they have yielded mixed findings.

To bridge this gap, The NHANES study, a large cohort representative of the U.S. population which provided a unique opportunity to examine the effects of current fiber intake on asthma and respiratory morbidity was undertaken by Muhammad A Saeed et al from the College of Medicine, Nebraska Medical Center.

Researchers examined the relationship between dietary fiber intake and asthma, respiratory symptoms, and inflammation among adults who participated in the 2007-2012 National Health and Nutrition Examination Survey (NHANES).

Data were analyzed from adults 20-79 years of age (n=13,147) with complete information on fiber intake, total calorie intake, body mass index (BMI), smoking status, and poverty level.

Fiber intake was categorized into quartiles; Q1 being the 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.

On analysis, the following reports emerged.

• 69.5% of participants were non-Hispanic white. 54.5% were non-smokers, and 7.8% had current asthma.
• After adjusting for co-variates, fiber intake was associated with asthma (p = 0.01), with an increased odds of asthma with lower fiber intake (Q1 vs. Q4, OR 1.4, 95% CI = 1.0-1.8, p = 0.027).
• There were significant interactions between fiber and sex and fiber and race/ethnicity; stronger associations were seen for women and non-Hispanic white adults.
• Low fiber intake (Q1) was associated with an increased odds of wheeze (OR 1.3, 95% CI = 1.0- 1.6; 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 to high fiber intake.
• The odds of having high CRP versus nonPage 2 of 26 ANNALSATS Articles in Press. Published May 05, 2020, as 10.1513 detectable CRP were 1.6 times higher in the low fiber group (Q1) compared to high fiber group (Q4; OR 1.6, 95%CI = 1.0-2.5).

"In conclusion, our study suggests that a high fiber diet may play an important role in mediating systemic inflammation and respiratory morbidity, including adult asthma. For asthma, the interactions between sex and racial groups with fiber suggest a high fiber diet may be more protective in women and certain racial groups. These findings support dietary guidelines by the U.S. Department of Health and Human Services recommending that Americans consume 20-35 g/day of both soluble and insoluble fiber."said the team.

For full article click on link: https://doi.org/10.1513/AnnalsATS.201910-776OC

Primary source: Annals of the American Thoracic Society