Summary and Concluding Remarks
In summary, fibers are essential components of a healthy diet with multiple health benefits, and fiber intake has decreased at the same time as allergy rates have increased. There are a wide variety of fiber types, and specific fibers may contribute to maintaining a tolerogenic mucosal environment and may protect against allergic disorders. However, the optimal prevention or treatment strategies involving fibers in humans have yet to be defined. One mechanism by which fiber impacts the immune system is dependent on microbial fermentation and secretion of bioactive metabolites. Thus, fiber supplementation alone may not be sufficient and simultaneous replacement of missing microbes may be required for optimal benefits to be observed. Given the varied functional properties of different fiber types, it is unlikely that one type of fiber will provide all immune-relevant signals, and regular consumption of diverse fiber types may be superior to supplementation with individual fibers, which is consistent with our previous recommendations regarding the importance of dietary diversity in general for allergy prevention.60 However, as our understanding progresses on the role and mechanisms mediating specific fiber-microbiota-immune interactions, there is significant potential for using fiber in targeted manipulations of the gut microbiome and its metabolic functions in promoting immune health. We suggest that the current classification of different dietary fiber types would benefit by being updated to include their specific immune functional properties. Overall, fiber diversity may be more important immunologically than any single individual fiber type.
We also need to be aware of potentially inconsistent fiber effects across different disease endotypes, which depends on the distinct pathophysiological mechanisms in operation for the given endotype. This is of particular importance in studying heterogeneous diseases like allergic diseases and asthma and highlight the need for sufficiently powered studies. Deciphering the molecular alphabet that underpins this cellular dialogue is a significant challenge, but one that once overcome will yield the critical insights needed to prevent and treat allergic disorders in the 21st century. Future research on fiber-microbe-host interactions should be strongly encouraged as these discoveries will provide fundamental knowledge on the molecular communication networks that underpin life as a multicellular metacommunity and will progress our appreciation for the principle of biological diversity as a driver of physiological resilience and immune tolerance.
Conflict of interest Dr. Venter reports personal fees from Danone, personal fees from NNI, personal fees from Abbot, grants and personal fees from Reckitt, grants from Peanut board, personal fees from Before brands, personal fees from Else nutrition, personal fees from Sifter, outside the submitted work; BVB reports personal fees from Marfo Food Group, Lelystad, The Netherlands, personal fees from Abbott, grants from Nutricia Research, outside the submitted work; RM reports other from Nestle, grants and personal fees from Nutricia/Danone, personal fees from Mead Johnson, personal fees and other from Abbott, outside the submitted work. LOM received research grants from GSK and Chiesi, speaker support from Nestle, Nutricia, Reckitt and Abbott, consultant to Precision Biotics. CA received Research grants from Allergopharma, Idorsia, Swiss National Science Foundation, Christine Kühne-Center for Allergy Research and Education, European Commission’s Horison’s 2020 Framework Programme “CURE”, Novartis Research Institutes and Astra Zeneca. Took part in the advisory board and received research grants from Glaxo Smith-Kline,  Sanofi/Regeneron, Scibase,  Novartis. He is the Editor-in-Chief of Allergy. Dr. Pali-Schöll reports personal fees from Bencard Allergie GmbH outside the submitted work. Peter Smith declares that he has been paid an honorarium for working on the Nestle Nutrtiion Insitute advisory board. He also has received honorarium and/or speakers fees for Viatris, GSK, AZ, Sanofi, Mundipharama, Nutricia. He also has researcher initiated funding from Viatris, GSK and Sanofi. Dr. Agache is Associate Editor Allergy and Clinical and Translational allergy. Dr. Greenhawt is a consultant for Aquestive; is a member of physician/medical advisory boards for DBV Technologies, Sanofi/Regeneron, Genentech, Nutricia, Novartis, Acquestive, Allergy Therapeutics, ALK-Abello, AstraZeneca, Allergenis, and Prota; is a member of the scientific advisory council for the National Peanut Board; is a member of the Brighton Collaboration Criteria Vaccine Anaphylaxis 2.0 working group; is the senior associate editor for the Annals of Allergy, Asthma, and Immunology, and is member of the Joint Taskforce on Allergy Practice Parameters. He has received honorarium for lectures from ImSci, MedLearningGroup, the Allergy and Asthma Foundation of America, The Intermountain West Allergy Society, the Wisconsin Allergy Society, the Los Angeles Society of Allergy and Immunology, the Northern Califorina Society for Allergy and Immunology, and the Candian Society for Allergy and Clinical Immunology. IM reports personal fees from ALK-Abello, personal fees from Beiersdorf Dermo Medical GmbH, personal fees from Nestlé Deutschland GmbH, personal fees from Nutricia Milupa GmbH, personal fees from Sanomega GmbH, outside the submitted work; MS reports grants from Swiss National Science Foundation, grants from GSK, outside the submitted work. The other authors have not conflict to declare (CR, CA, KA-P, JW, MF, BN, LJ, KG, EU, KH-S, EV).