The Association Between Maternal Diet and the Human Milk Microbiome: A Review of Evidence and Methodological Challenges.

The human milk (HM) microbiome plays an important role in shaping the infant gut microbiota, with potential implications for immune development and both short- and long-term health. Among the maternal and infant factors influencing HM microbial composition, maternal diet represents a modifiable determinant. However, evidence regarding the impact of diet on the HM microbiota remains limited, and the methodological quality of available studies is variable. This review synthesises findings from 15 observational and interventional studies, critically evaluating dietary assessment approaches, milk collection protocols, microbiome analysis methods, and control of confounding factors. Current evidence suggests that maternal intake of macronutrients, micronutrients, and bioactive compounds may influence HM bacterial composition and functional potential, though results are inconsistent. Key limitations across studies include small sample sizes, short intervention periods, lack of appropriate control groups, variable aseptic sampling methods, inadequate contamination controls, and insufficient adjustment for confounders. To advance the field, we recommend larger, multicentre randomised controlled trials with longer intervention durations, incorporation of dietary biomarkers, standardised HM collection and processing protocols, and advanced multi-omics approaches. Strengthening methodological rigour is essential to generate robust evidence that can guide dietary interventions aimed at optimising the HM microbiota and improving infant health outcomes.