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

## TL;DR

A Mediterranean-style diet during pregnancy is linked to healthier infant gut microbiota through effects on maternal gut bacteria.

## Contribution

Identifies maternal Coprococcus as a key mediator linking gestational diet to infant gut microbiota composition.

## Key findings

- Higher Mediterranean diet scores correlated with increased infant gut diversity and lower Veillonella abundance.
- Maternal Coprococcus mediated the link between diet and infant microbiota, reducing Veillonella in infants.
- Pro-inflammatory diets were associated with higher infant Veillonella and lower gut diversity.

## Abstract

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.

The online version contains supplementary material available at 10.1007/s00394-026-03909-9.