Breastmilk contains many prebiotics to support the growth of beneficial bacteria in the infant’s gut. It also contains bacteria that seed the infant’s gut. Previous research has shown that the bacteria in breast milk do indeed take hold and colonize the gut, and so it is imperative to infant microbiome development. An article published last week sought to discover if the breastmilk microbiome changes depending on mode of delivery, especially since we have seen that C-section infant’s have much different microbiomes than their vaginally delivered counterparts. The scientists published their results in the journal Microbiome.

The scientists tested the breastmilk of 39 Canadian women. Despite various backgrounds, each woman’s milk was dominated by Staphylococcus, Enterobacteriaceae, and Pseudomonas. Moreover, there were not major differences in the breast milk microbiomes between modes of delivery, showing that it is not effected by C-section of vaginal birth. In addition, the gender of the baby did not change the microbiome either. Interestingly, the microbiomes were very different between mothers, meaning that babies are being exposed to highly diverse bacteria from milk. In one case 80% of the bacteria were staphylococci, and in another case more than 50% was Pseudomonas.

There is little evidence that shows how differences in breast milk microbiomes are affecting children. That said, we know the microbiome is critical to immune system development, and therefore it reasons that these differences may be important. In any event, it is useful to see that mode of delivery itself is unlikely to change the breastmilk microbiome.

Human breast milk contains nutrients and compounds that are beneficial for infants. Human milk oligosaccharides (HMOs) are a group of important complex carbohydrates that are found in breast milk. These HMOs are important in the developing infant because they serve as a prebiotic, helping to shape the infant’s gut microbiome by facilitating the selection of beneficial bacteria. The link between gut microbiota composition and infant obesity has led to speculation that HMOs might affect certain bacteria that in turn lead to decreased body fat. Because HMO composition of female breast milk varies over the course of lactation, researchers in Oklahoma and California tested to see whether differences in milk HMO content are associated with infant body weight. The results of their study were published in The American Journal of Clinical Nutrition.

Twenty-five mother-infant pairs participated in this study. On average, the mothers were 29.5 years of age and overweight before conception. When the infants were 1 month and 6 months old, the mothers supplied breast milk samples to test for HMO composition. Concurrently, the infants’ body fat composition, weight, and length were measured.

The findings suggest that HMOs are associated with infant body weight, fat mass, and lean mass at both 1 month and 6 months. A diversity of HMOs, such as LNFFPI (lacto-N-fucopentaose I, a sugar), DSLNT (difucosyl-LNT, a sugar), and FDSLNH (fucosyl-disialyl-lacto-N-hexaose, a sugar) accounted for 33% of the fat mass, which was more than other variables such as gender, and mothers’ pregnancy BMI. infant fat mass than did sex, pregnancy BMI. LNFPI was inversely associated with 1 month old infant weight, while at 6 months it was inversely associated with weight, lean mass, and fat mass. Overall, the presence of a diverse group of HMOs decreased infant body mass. While this study has its limitations because it does not specifically test the bacterial composition of the gut, it is a first step to identifying an association between HMOs and infant BMI. As obesity remains an epidemic in the United States, perhaps the microbiome is the first place to look towards to prevent the disease.