From bench to bedside. High fiber foods: a good ally in asthma therapy?
Asthma is a common disease but its pathogenesis is still under study. There are several environmental factors that seem to affect the onset and the evolution of the disease and diet might play an important role.
This hypothesis was initially driven by the results obtained on mice on high-fiber diet. The fibers modified the intestinal microbioma resulting in regulatory T (T reg) cells stimulation and reduction of airways inflammation (Trompette A 2014, Thorburn AN 2015).
Fibers are digested by the intestinal flora which produces short chain fatty acids (SCFA): acetate, butirrate and propionate. Once absorbed by the colon epithelial cells, SCFA enter the circulation and modulate the activity of the immune system through the G-protein coupled receptors (GPR) 41 and 43 of monocytes and lymphocytes. The effects include: inhibition of chemotaxis and cell adhesion by reduction of tissue lymphocyte infiltration, down-regulation of some inflammatory cytokines (TNFalfa, IL-6, IL-1 beta, IFNg), up-regulation of anti-inflammatory cytokines such as IL-10 and activation of T cells.
Based on the results obtained in the laboratory, an Australian research group (Halnes I 2017) recently documented in 17 subjects with asthma the short-term effect of a diet rich in fibers (3.5 g of inulin) and probiotics: after 4 hours FeNO decreased and the induced sputum showed a significant reduction in lymphocytes, macrophages, neutrophils and IL-8. The increased gene expression of GPR41 and 43 demonstrated that these effects might have determined by SCFA which in subjects with asthma can activate these receptors on respiratory system cells.
This is the first time that the potential anti-inflammatory effect of fibers in the lung is reported in humans. Bigger studies are needed but if these findings are confirmed high fiber foods may be a valuable help in asthma control.
Thorburn AN, McKenzie CI, Shen S, Stanley D, Macia L, Mason LJ, Roberts LK, Wong CH, Shim R, Robert R, Chevalier N, Tan JK, Mariño E, Moore RJ, Wong L, McConville MJ, Tull DL, Wood LG, Murphy VE, Mattes J, Gibson PG, Mackay CR. Evidence that asthma is a developmental origin disease influenced by maternal diet and bacterial metabolites. Nat Commun. 2015 Jun 23;6:7320
Trompette A, Gollwitzer ES, Yadava K, Sichelstiel AK, Sprenger N, Ngom-Bru C, Blanchard C, Junt T, Nicod LP, Harris NL, Marsland BJ. Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis. Nat Med. 2014 Feb;20(2):159-66
Halnes I, Baines KJ, Berthon BS, MacDonald-Wicks LK, Gibson PG, Wood LG. Soluble Fibre Meal Challenge Reduces Airway Inflammation and Expression of GPR43 and GPR41 in Asthma. Nutrients. 2017 Jan 10;9(1)