Impact of Diet on the Maternal and Infant Microbiota ^†

Whilst diet plays a pivotal role in human health, very little research on the lactation period exists. Research studying the influence of maternal nutrition on maternal health, milk composition and infant health provides conflicting results [1]. It is often hypothesized that the maternal diet influences the maternal condition (e.g., microbiome and body composition), which in turn influences milk composition (e.g., microbiome, macronutrients, hormones, and immune proteins) and then impacts the infant (e.g., gut microbiome). We conducted a within-participant intervention, where maternal meals with reduced fat and sugar and increased fiber were provided for 2 weeks after a 1-week dietary monitoring period. Shotgun metagenomic sequencing of stool samples from 10 infants (n = 20, one sample pre-diet and one post-diet) revealed no differences in the microbiome composition. However, changes in maternal fiber, sugar and fat intake were associated with changes in the functional potential of the infant gut microbiome [2]. To determine changes in the maternal gut microbiome in response to the dietary intervention and subsequently the human milk microbiome, we analyzed fecal swabs and milk samples collected from 11 mothers prior to the intervention, post-intervention, and 4 and 8 weeks post intervention. Small but significant changes were found in the relative abundance of two fecal bacteria immediately post intervention: Bacteroides caccae (decreased) and Faecalibacillus intestinalis (increased); however, seven bacteria changed in the 4 to 8 weeks post intervention. Similarly, the abundance of two bacteria changed in human milk; Cutibacterium acnes increased and Haemophilus parainfluenzae decreased. Two additional human milk bacteria differed in the 4-to-8-week intervention follow-up period [3]. Interestingly, we found no differences in the macronutrient content in the daily human milk samples across the full 3-week period [4]. Conversely, after the dietary intervention, the insulin, leptin and adiponectin concentrations in human milk were decreased by 10–25%. This is likely due to the significant reduction in the maternal body weight (−1.8%) and fat mass (−6.3%). Analysis of the immune proteins lactoferrin and lysozyme in daily milk samples across the 3-week study period showed a relatively small but significant decrease in lactoferrin. This may reflect an improved maternal inflammatory status [5]. Further, the short-term diet had no effects on 24 h milk production or infant growth [6].