Study examines the relationship between exclusive human milk consumption and gut microbiota in preterm infants

By Tarun Sai LomteReviewed by Benedette Cuffari, M.Sc.Mar 6 2023

In a recent study published in JAMA Network Open, researchers examine the impact of an exclusive human milk diet on the infant gut microbiome.

Study: Effect of an Exclusive Human Milk Diet on the Gut Microbiome in Preterm Infants: A Randomized Clinical Trial. Image Credit: Iryna Inshyna / Shutterstock.com

Benefits of breast milk

Receipt of a mother’s breastmilk is associated with improved metabolic and cognitive outcomes, as well as reduced neonatal morbidity rates in preterm infants. However, a shortfall in supply necessitates using pasteurized human milk or bovine formula.

There remains a lack of randomized clinical trials (RCTs) that have determined the optimal supplement for infants when the mother’s milk supply is insufficient. One previous meta-analysis reported reduced necrotizing enterocolitis (NEC) rates in infants exclusively fed human donor milk compared to formula-fed infants. However, this difference was insignificant in studies when formula was only used as to supplement.

Some of the different mechanisms by which breast milk might reduce the risk of NEC include the lack of bovine antigens within breast milk that may cause a reaction in the infant. In addition, the presence of specific functional components within breast milk, such as lactoferrin and human milk oligosaccharides (HMOs), may also exert certain beneficial effects on the gut microbiota.

About the study

In the present RCT, researchers determine the effect of an exclusive human milk diet on the gut microbiome in preterm infants. Herein, preterm infants from four NICUs in the U.K. were recruited for inclusion in the study within 72 hours of life who had only received mothers’ breastmilk. Infants with congenital and life-threatening conditions were excluded.

Infants were randomized to intervention (exclusive human milk diet) and control (standard diet) arms. Feeding in the control arm included using the mother’s breastmilk and preterm formula milk to compensate for the shortfall in breastmilk supply. Infants in the intervention arm were fed breastmilk and a pasteurized human milk product to make up for the breastmilk shortfall.

Control group infants received a bovine-derived fortifier, whereas those in the intervention arm received a human milk-derived fortifier. Infants continued to receive their assigned diets until 34 weeks post-menstrual age (PMA).

Morbidity and weight gain data were obtained until discharge. Then, data on demographics and outcomes were captured using medical records and the National Neonatal Research Database.

Stool samples were collected daily and analyzed at baseline, the tenth day of life (DOL), full feeds, DOL 21-28, and the final sample at 34 weeks’ PMA. Stool samples were subjected to DNA extraction and sequencing, V4 16S rRNA sequencing, as well as analysis of Shannon diversity and bacterial richness. Multiple cross-sectional analyses were performed to identify covariates associated with metagenomic profiles.

Findings

The team recruited 126 preterm infants from September 2017 to September 2019. Sixty-three infants were randomized to the control group and the remaining to the intervention arm.

Eighty-six infants were born before 28 gestational weeks. Four infant deaths among controls and eight from the intervention arm were recorded at a median post-natal age of 25 and 15 days, respectively.

Ready-to-feed human or formula milk represented less than 1% of fluid intake in infants who died. Although surgical NEC affected one infant from each cohort, NEC was not the primary cause of death.

The team analyzed 472 stool samples from 116 subjects. First, the authors observed a significant association between the NICU site and probiotic use with bacterial profiles. The trial group (control or intervention) was not associated with bacterial profiles at any time.

Generalized linear mixed models revealed that trial groups were not associated with bacterial richness or Shannon diversity differences. However, analysis of final stool samples showed that Shannon diversity and richness were associated with the trial group. Corynebacterium and Staphylococcus negatively correlated with DOL, whereas Veillonella, Escherichia, Enterobacter, Bifidobacterium, and Clostridium showed positive correlations.

Additionally, the relative abundance of Bifidobacterium in infants from NICUs using probiotics was higher. Furthermore, Bifidobacterium abundance was negatively correlated with the number of days on antibiotics and positively correlated with the number of days on mothers’ milk. The intervention arm was significantly associated with a lower relative abundance of Lactobacillus.

Conclusions

The current study investigated the effect of an exclusive human milk diet on the infant gut microbiome. The researchers found no effect of the trial group on Shannon diversity or microbial richness; however, infants in the intervention arm had different microbiome profiles that were not replicated in weighted analyses. Thus, an exclusive human milk diet affected taxa like Lactobacillus with low abundance, which was lower in intervention group infants.