In a recent study published in PLOS One, researchers reviewed current literature to determine correlations between human milk microbiota and maternal weight based on pregnancy and postpartum body mass index (BMI) and gestational weight gain (GWG).
Recent research on gut microflora has highlighted the importance of gut microbial diversity in metabolic processes such as energy uptake from diet. Obesity has been linked to the low diversity of the gut microbiome, resulting in improper energy management and low-grade systemic inflammations in the body.
The health of the mother during and after pregnancy can influence the health and development of the infant. Studies have found that maternal obesity can alter maternal gut biota and has been associated with an increased risk of metabolic syndrome and childhood obesity in the offspring. The gut microbiota of the infant is thought to be initially assembled partly through the microbial composition of human milk, and studies have found that the composition of the gut microbiome during early infancy influences various health outcomes.
While extensive research exists on the effect of maternal obesity on maternal gut biota, little is known about its effect on other maternal microbiomes, such as milk microflora composition.
About the study
In the present study, the researchers conducted a scoping review to gather broad evidence and understand key concepts about the association between maternal obesity and the microbial composition of human milk. Various databases, including MEDLINE, Embase, Web of Science, and Scopus were used to gather relevant literature.
Cohort, cross-sectional, longitudinal, experimental, and observational studies on associations between human milk microbiota and maternal weight published in peer-reviewed journals were included in the study. The descriptions of maternal weight included pre-pregnancy or postpartum BMI or percentage body fat, GWG, or gestational change in BMI.
Human milk microbiome assessment methods were culture-dependent or culture-independent. The culture-independent methods include metagenomics, next-generation sequencing (NGS), amplicon analysis, quantitative polymerase chain reaction (qPCR), and gel electrophoresis. Culture-dependent methods include the culturing, isolation, and phenotypic or genotypic characterization of the bacteria.
Studies that reported gestational diabetes, mastitis, and smoking behavior in the participants were excluded as these factors were known to affect human milk composition.
The findings of the study were ambiguous, and the results suggested a minor association between the microbial composition of human milk and maternal weight status. Of the 20 relevant studies from the 6,365 screened, 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 human milk microflora.
The review found that human milk microbial communities were similar to skin microbiota and consisted mostly of Staphylococcus, Streptococcus, and Acinobacter. Higher maternal BMI and GWG were generally associated with lower alpha diversity, lower Bifidobacterium, and higher Staphylococcus, and Streptococcus abundance compared to mothers with normal BMI and GWG.
However, only minor correlations were found between microbial milk composition and maternal weight, for which the authors presented three explanations. Firstly, the changes in maternal gut microbiota associated with GWG and postpartum BMI increase could result in changes in milk microbial composition. Studies have found that women with GWG and obesity have higher Staphylococcus and lower Bifidobacterium abundance in their gut and subsequently in the milk, with the bacteria potentially populating the milk through skin microbiota.
Secondly, the dietary intake of mothers can influence the microbial milk composition directly or indirectly through milk macronutrient and oligosaccharide compositions. The diet during pregnancy and postpartum also directly affects maternal BMI and GWG, explaining the link between maternal weight and milk microbiome composition.
Lastly, the authors believe breastfeeding practices can influence milk microbiota. Obesity and high GWG in mothers have resulted in shorter breastfeeding sessions, possibly due to various psychological, physiological, and cultural factors. Studies have found that shorter breastfeeding duration alters the milk macronutrient and microbiome composition by limiting how long the milk is exposed to the skin microbes around the areola and the oral microbes in the infant’s oral cavity.
Furthermore, the milk microbiome can also change according to the lactational stage. The review discussed a study in which the total bacterial content and abundance of Bifidobacterium, Staphylococcus, and Lactobacillus increased with progressive stages of lactation.
Overall, the review found minor associations between human milk microbial composition and maternal weight status. According to the authors, the association can be explained by changes in maternal gut biota, dietary intake during and after pregnancy, and the duration of breastfeeding.