Maternal Dietary Intervention during Lactation Impacts the Maternal Faecal and Human Milk Microbiota

Diet is a key factor that shapes the gut microbiome. Maternal diet has been proposed as a potential modulator of the human milk microbiome. However, the effect of diet during lactation on the maternal microbiota remains unclear. This study, therefore, set out to determine the effect of a two-week reduced fat and sugar and increased fibre maternal dietary intervention on the maternal faecal and milk microbiota. Faecal swabs and human milk samples were collected from mothers (n = 11) immediately pre-intervention, immediately post-intervention, and 4- and 8-weeks post-intervention, and were analysed using full-length 16S rRNA gene sequencing. The maternal macronutrient intake was assessed across one week prior to the intervention using 24 h dietary recall and during the intervention using FoodWorks 10 Software. The maternal fat and sugar intake significantly decreased from pre-intervention (fat: 120.9 ± 39.4 g; sugar: 114.1 ± 40.9 g) to the first (fat: 52.9 ± 4.3 g, p < 0.001; sugar: 83.2 ± 5.1 g, p = 0.005) and second week of the intervention (fat: 52.3 ± 6.2 g, p < 0.001; sugar: 82.7 ± 6.5 g, p = 0.005). The dietary fibre intake significantly increased from pre-intervention (28.8 ± 8.3 g) to the first week of the intervention (34.6 ± 2.8 g, p = 0.012) but was not different in the second week of the intervention compared to pre-intervention. Significant changes in the bacterial composition of maternal faeces were detected after the dietary intervention, with decreases in the relative abundance of Bacteroides caccae and increases in the relative abundance of Faecalibacillus intestinalis. In human milk, a significant increase in Cutibacterium acnes and a decrease in Haemophilus parainfluenzae were detected. Significant differences in maternal faecal and human milk bacterial composition were maintained 4 to 8 weeks after the intervention. This pilot study demonstrates that short-term changes in maternal diet during lactation can alter the maternal faecal and human milk microbiota.