The Tummy Trial: The effect of omega-3 supplementation in breast-feeding mothers on the microbiome composition of their baby – a randomised controlled trial

Establishment of the infant gut microbiome plays an important role in the development of intestinal and systemic immunity. Dietary exposures during early life are known to influence intestinal microbiome characteristics, however, the role of specific dietary factors is poorly understood. Preclinical and clinical studies have suggested that omega-3 long-chain polyunsaturated fatty acids (LCPUFA), particularly docosahexaenoic acid (DHA), may have beneficial effects of the gut microbiome and gut health. However, whether omega-3 LCPUFA can positively influence the development of the microbiome in early infancy has yet to be determined.This study aimed to determine the effect of supplementing breast-feeding mothers with a high-dose omega-3 LCPUFA supplement on the composition of the infant's faecal microbiome in the 12 weeks post-partum.Mothers who had delivered vaginally at term and intended to exclusively breast-feed for 12 weeks post-partum were recruited within 7 days of delivery and were randomly allocated to receive either high-DHA fish-oil capsules (providing 1000mg of DHA and 300mg of EPA/day) or placebo capsules from enrolment to12 weeks post-partum. The primary outcome was the composition of the infant faecal microbiota, as determined by 16S ribosomal RNA gene amplicon sequencing. Secondary outcomes were maternal faecal and breast milk microbiota composition at 12 weeks post-partum Sub-group analyses were conducted for those infants who were exclusively breast-fed for the full 12 weeks.72 mother/infant dyads were randomized, of which 62 (86.1%) completed the study. Infant faecal microbiota composition, alpha and beta diversity, did not differ significantly between intervention and placebo groups, either in the whole population of in the sub-group of infants who were exclusively breast-fed for the 12 weeks. The composition of the maternal faecal microbiome was also not different between groups at either 6 or 12 weeks post-partum. The beta diversity of the breast milk microbiome, however, was significantly different between the intervention and placebo groups at the end of the intervention period (P=0.0375) suggesting a difference in the microbial community structure between groups, however no specific bacteria were identified as significantly different.Maternal high-dose DHA supplementation during breastfeeding alters the composition of the breast milk microbiome in the first 12 weeks post-partum, but does not appear to significantly influence the composition of either the maternal or infant faecal microbiome during this period. This suggests that maternal DHA supplementation does not markedly promote the development of the infant gut microbiome in healthy term-born infants delivered vaginally.