Systematic Review: Importance of fibers for allergy prevention and treatment
For the purposes of this review, we focused on studies published during the last 5 years. In our search, we included observational epidemiological studies and clinical trials/intervention studies with application of dietary fiber and/or prebiotics to prevent or treat allergic diseases. Search terms are given in supplement 1 . Based on these, 542 papers (235 from Pubmed and 307 from EMBASE) were retrieved. After removal of duplicates, 512 papers remained. Finally, after abstract and full text screening, we identified 16 studies that involved either dietary prebiotic (n=7) or fiber (n=9) intake and measured allergy-relevant outcomes. Exposures, interventions, and outcomes were deemed to be too heterogeneous with respect to prebiotic/fiber type and assessment of the outcome to attempt to pool the data for meta-analysis, so results are summarised as a narrative systematic review only.
Several guidelines and systematic reviews have previously examined the role of both fiber and prebiotic supplementation with respect to allergy outcomes. A 2015 review by Orel et al. concluded that “the strongest evidence on beneficial effects of prebiotics in children exists in relation to the fight against constipation, poor weight-gain in preterm infants and prevention of eczema in atopic children.”37 The World Allergy Organization (WAO) GLAD-P document stated that prebiotics could be added to the diet of not-exclusively breastfed infants, both at high and at low risk for developing allergy, however not in exclusively breastfed infants. This is a conditional recommendation with very low certainty of evidence.38 The supporting GRADE analysis for this document regarding the use of prebiotics given to infants stated there is “a possible effect of prebiotic supplementation in infants on the reduction in the risk of asthma or wheezing”, in that prebiotics might reduce the risk of recurrent wheezing in infants, but this had a very low level of certainty due to “risk of bias, indirectness of the evidence, and imprecision due to low number of events of the estimated effect”.39 The Philippine guidelines on dietary primary prevention state that prebiotics are not recommended to prevent allergic diseases (with a strong recommendation level due to low quality evidence).40 A systematic review from the United Kingdom on dietary recommendations for infants and pregnant or lactating mothers also reports that there is no clear evidence that prebiotic supplementation reduces eczema at age ≤ 4 years (RR 0.75; 95% CI 0.56±1.01; I2 = 57%) and no association at age 5 to 14 years.41 This was followed by a systematic review from Skorka et al.42 who noted inconclusive effects of prebiotic supplementation in infant formula in influencing the development of allergic diseases, with only a possible (though methodologically limited) single study noting supplementation of infant formula with GOS/FOS may decrease “some allergic reactions” and GOS/FOS/AOS supplementation may reduce the risk of eczema. Lastly, a systematic review supporting the new EAACI food allergy prevention guidelines noted little to no effect for the role of prebiotics, though also stated that the evidence for this is very limited.43