From Diet to Dysbiosis: How Nutritional Factors Shape Gut Microbiota and Drive Airway Inflammation in Pediatric Asthma

Asthma prevalence in school-age children varies widely by geography, from below 5% in some regions to above 20% in others, averaging 10–12% across industrialized countries, but genetic factors account for less than 40% of disease liability. Gut microbiota is increasingly recognized as a critical intermediary between early-life dietary exposure and immunological trajectories that determine asthma susceptibility. Through the production of short-chain fatty acids (SCFAs), particularly butyrate, propionate, and acetate, commensal bacteria regulate dendritic cell function, promote T-regulatory (Treg) cell differentiation, and attenuate Th2-polarized airway inflammation via the gut–lung axis. Epidemiological cohorts including CHILD, WHEALS, and PASTURE associate early-life dysbiosis and reduced Lactobacillus, Bifidobacterium, and Faecalibacterium prausnitzii with increased asthma risk, while dietary patterns rich in fermentable fibre, omega-3 polyunsaturated fatty acids, and diverse plant-based foods are associated with preserved microbial diversity and, in preclinical models, attenuated type-2 inflammatory signalling. This narrative review synthesizes mechanistic and epidemiological evidence on how nutritional exposures shape gut microbiota composition and influences asthma onset and severity in paediatric populations, including the distinct obesity-related asthma phenotype. Critical gaps, insufficient dietary intervention trials with microbiome endpoints, methodological heterogeneity across cohorts, and the paucity of data from non-Western populations are discussed, with implications for preventive nutritional counselling in paediatric allergology practice.