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Nutrition research review: Role of dietary fibre in promoting immune health – An EAACI position paper. 

Dietary fibre is an important factor in determining the gut microbiome and influence the immune system. Dietary fibre-derived metabolites are involved in immune cell decision-making processes, giving rise to the suggestion that the trend over time towards lower intakes of dietary fibre is contributing to the rise in allergic and hypersensitivity disorders.

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Dietary fibre: the non-digestible component of food made up of carbohydrate polymers and oligomers. Dietary fibres are not digested or absorbed in the small intestine and so they pass into the large bowel. Their varied characteristics such as solubility, viscosity and fermentability determine their functional role in the gut and how accessible they are to microbes.

Prebiotics: a subset of dietary fibres that when utilised by microorganisms confers a health benefit to the host (Gibson et al., 2017). Common prebiotics include fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and inulin.

Dietary sources of dietary fibre: fruits, vegetables, nuts, seeds, wholegrains.

Dietary fibre recommendations for Australian adults (NHMRC Nutrient Reference Values, 2013):

• Men: 30 g/d
• Women: 25 g/d

Direct effects of dietary fibre on the immune system include modulation epithelial and immune cells. For example, Galacto-oligosaccharides (GOS), inulin, pectin, and β-galactomannan support the function of the intestinal epithelial barrier. Fibres such as inulin, GOS, fructo-oligosaccharides (FOS) can modulate cytokine and chemokine secretion from epithelial, macrophage and dendritic cells.

Upon fermentation, many of the metabolites that are produced have immune effects. Short chain fatty acids (SCFA) e.g., acetate, butyrate, and propionate, are metabolites that are also immunomodulators. For example, they influence: IL-10 secretion, Treg numbers and effectiveness, bone marrow haematopoiesis, they dampen effector T cell activity, inhibit mast cell degranulation, and more. Empirical studies have found SCFA intake to be protective against colitis, inflammatory arthritis, RSV, and both airway and food allergies.

In this narrative review, Venter and colleagues explored the role of dietary fibre in preventing allergic disease, drawing on studies from 2015 to 2020, reported the following:

• Some evidence that a higher intake of dietary fibre has protective effects for respiratory symptoms but most studies were small observational studies that did not label the type of dietary fibre that was consumed.
• Small, poor-quality trials have found some potential association between fibre and prebiotics on allergic rhinitis outcomes.
• Data from limited studies show that when given to children at high risk of allergy, prebiotics had no impact on eczema development to one year of age.
• No studies were included that focussed on dietary fibre or prebiotics and food allergy outcomes.

The optimal dietary fibre intervention has not yet been identified. The authors suggest it would be useful for future research to explore whether including pro-biotics alongside prebiotics, as opposed to simple supplementation, improves outcomes. In addition, it is worthwhile to consider whether it is the overall pattern of dietary fibre that has more of an influence on the immune system, as opposed to any one dietary fibre type. Indeed, the authors agree that more research is needed to expand our knowledge of the influence of dietary fibre on the immune system.

Such research will provide insights that will inform the solutions to the complex problems posed by allergic diseases.

– Anna Millichamp, APD, Senior Teaching Fellow, PhD Candidate, Bond University

Full paper

Venter, C, Meyer, RW, Greenhawt, M, et al. Role of dietary fiber in promoting immune health—An EAACI position paper. Allergy. 2022; 77: 3185- 3198. doi: 10.1111/all.15430

Available here: https://onlinelibrary.wiley.com/doi/10.1111/all.15430