What is the relationship between maternal weight status and milk microbiome composition?

What is the relationship between maternal weight status and milk microbiome composition?

In a recent study published in Plus one Researchers reviewed the current literature to determine correlations between breast milk microbiota and maternal weight based on pregnancy and postpartum body mass index (BMI) and gestational weight gain (GWG).

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background

Current research on intestinal flora has highlighted the importance of microbial diversity in the intestine for metabolic processes such as energy absorption from food. Obesity is associated with the low diversity of the gut microbiome, which leads to improper energy management and low-grade systemic inflammation in the body.

The mother's health during and after pregnancy can influence the health and development of the infant. Studies have found that maternal obesity can alter the mother's gut biota and is associated with an increased risk of metabolic syndrome and childhood obesity in the offspring. The infant's gut microbiota is initially thought to arise in part from the microbial composition of breast milk, and studies have found that the composition of the gut microbiota in early infancy influences various health outcomes.

While there is extensive research on the effects of maternal obesity on the mother's gut biota, little is known about its effects on other maternal microbiomes, such as the composition of the milk microflora.

About the study

In the present study, researchers conducted a scoping review to collect comprehensive evidence and understand key concepts about the association between maternal obesity and breast milk microbial composition. Various databases were used to collect relevant literature, including MEDLINE, Embase, Web of Science and Scopus.

The study included cohort, cross-sectional, longitudinal, experimental and observational studies on associations between breast milk microbiota and maternal weight published in peer-reviewed journals. Maternal weight descriptions included prenatal or postpartum BMI or percent body fat (GWG) or change in BMI during pregnancy.

The methods used to assess the breast milk microbiome were culture-dependent or culture-independent. Culture-independent methods include metagenomics, next-generation sequencing (NGS), amplicon analysis, quantitative polymerase chain reaction (qPCR), and gel electrophoresis. Culture-dependent methods include cultivation, isolation and phenotypic or genotypic characterization of the bacteria.

Studies that reported participants' gestational diabetes, mastitis, and smoking habits were excluded because these factors were known to influence the composition of breast milk.

Results

The results of the study were inconclusive and suggested little association between the microbial composition of breast milk and the mother's weight status. Of the 20 relevant studies of the 6,365 studies examined, 11 reported significant associations between the two variables, four reported both significant and null associations, and five reported only null associations between maternal weight status and breast milk microflora.

The review found that the microbial communities in breast milk were similar to the skin microbiota and consisted mainly of Staphylococcus, Streptococcus and Acinobacter. Higher maternal BMI and GWG were generally associated with lower alpha diversity, lower bifidobacteria content, and higher frequencies of staphylococci and streptococci than mothers with normal BMI and GWG.

However, only low correlations were found between milk microbial composition and maternal weight, for which the authors put forward three explanations. First, the changes in maternal gut microbiota associated with GWG and an increase in postpartum BMI could lead to changes in the microbial composition of milk. Studies have found that women with GWG and obesity have higher frequencies of staphylococci and lower frequencies of bifidobacteria in their gut and subsequently in their milk, with the bacteria possibly entering the milk via the skin microbiota.

Second, maternal dietary intake may influence milk microbial composition directly or indirectly through milk macronutrient and oligosaccharide compositions. Diet during pregnancy and postpartum also directly affects the mother's BMI and GWG, which explains the connection between the mother's weight and the composition of the milk microbiome.

Finally, the authors believe that breastfeeding practices may influence milk microbiota. Obesity and high GWG in mothers have resulted in shorter breastfeeding durations, possibly due to various psychological, physiological and cultural factors. Studies have found that shorter breastfeeding duration alters the macronutrient and microbiome composition of milk by limiting how long the milk is exposed to skin microbes around the areola and oral microbes in the infant's oral cavity.

In addition, the milk microbiome can also change depending on the stage of lactation. The review discussed a study in which total bacterial content and abundance of Bifidobacterium, Staphylococcus, and Lactobacillus increased as lactation stages progressed.

Conclusions

Overall, the review found modest associations between the microbial composition of breast milk and the mother's weight status. According to the authors, the connection can be explained by changes in the maternal intestinal biota, food intake during and after pregnancy and the duration of breastfeeding.

Reference:

• Daiy, K. et al. (2022) „Maternal Weight Status and the Composition of the Human Milk Microbiome: A Scoping Review“, PLOS ONE, 17(10), S. e0274950. doi: 10.1371/journal.pone.0274950. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0274950

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