Novel insights into how gestational diet affects maternal-infant microbiota: a cross-sectional causal mediation analysis at one month postpartum

Maternal diet shapes maternal and infant microbiota, influencing early-life health. This study assessed associations between maternal dietary indices and infant gut microbiota, and the mediating role of maternal core taxa. In the MAMI cohort, pregnancy diet was evaluated using the Modified Mediterranean Dietary Score (MMDS), Dietary Quality Index (DQI), Healthy Eating Index (HEI), and Dietary Inflammatory Index (DII). Perinatal data, clinical records, and infant gut microbiota (1 month postpartum, 16S rRNA sequencing) were analyzed using clustering, regression, and causal mediation analysis (CMA). Among 104 mother–infant pairs, DII was inversely correlated with MMDS, HEI, and DQI. Higher MMDS (β = 0.785, p = 0.037) and lower DII (β = –0.783, p = 0.037) were associated with increased infant Veillonella relative abundance; MMDS was also positively linked to Shannon and Simpson diversity. In the maternal microbiota, Coprococcus correlated positively with MMDS and negatively with DII. CMA identified maternal Coprococcus as the strongest mediator, linking MMDS to lower infant Veillonella (a × b = –0.15) and DII to higher infant Veillonella (a × b = 0.15). A Mediterranean-style pregnancy diet was associated with greater infant gut diversity and, via maternal Coprococcus, lower Veillonella abundance, whereas a pro-inflammatory diet showed the opposite pattern. These findings highlight both direct and microbiota-mediated pathways linking maternal nutrition to early microbial programming. Clinical trial registry number: registration ID: NCT03552939 (date record study 2018–06-10). URL: https://clinicaltrials.gov/study/NCT03552939 .