Effects of feeding type on gut microbiota and atopic dermatitis in cesarean delivered infants: a combined birth cohort study

To investigate the effect of early feeding type on gut microbiota composition and atopic dermatitis (AD) development in cesarean-delivered infants, and to evaluate whether probiotic-supplemented formula can mitigate microbial and immunologic disadvantages associated with cesarean delivery. A total of 129 infants delivered by cesarean section were enrolled and classified into three groups: Group A (exclusively breastfed), Group B (fed standard formula), and Group C (fed probiotic-fortified formula). Stool samples were collected at 6–8 weeks of age and analyzed using 16S rRNA gene sequencing. Microbial diversity indices and taxonomic composition were compared, and the incidence of AD by 6 months was assessed. The incidence of AD by 6 months was 8.3% in Group A, 66.7% in Group B, and 25.0% in Group C (p = 0.793). Group A showed the highest gut microbial diversity (Shannon, Chao1, and observed amplicon sequence variants), with significantly lower diversity in Group C (adjusted p < 0.017). No significant differences were observed in the Simpson index. Group C exhibited a significantly higher relative abundance of Bifidobacterium compared with Groups A and B (adjusted p < 0.001), while Lactobacillus was most abundant in Group A, with significant differences across all groups (adjusted p < 0.001). The incidence of AD did not significantly differ between Group A and Group C . While early probiotic supplementation via infant formula may support beneficial bacterial colonization in cesarean-delivered infants, its potential role in AD prevention remains to be clarified through further longitudinal studies.