The influence of maternal metabolic phenotype on breast milk composition and on the maternal and infant urinary metabolome

Abstract

The main objective of my research is to describe the influence of maternal phenotype on human breast milk composition. My primary objective is to establish whether maternal Body Mass Index (BMI) influences breast milk metabolomic and endocrine profiles, macronutrient content, and maternal and infant urinary metabolomes.

I first focused on milk sample preparation techniques prior to metabonomic analysis. Due to milk containing complex structures, such as milk lipid globules and casein micelles, it is difficult to analyse because of interference with the analytical techniques employed. I therefore optimised sample preparation methods prior to analysis. I also conducted a systematic review of all published literature relevant to the hormonal content of human milk.

I investigated human milk metabolomic profiles using 1H NMR spectroscopy and liquid chromatography-mass spectrometry. I examined appetite regulating hormones using immunoassay techniques, and macronutrient content using mid infrared spectroscopy. I also investigated the metabolomic profile of mothers’ and infants urine using 1H NMR spectroscopy.

My principal conclusions from this work are that breast milk metabolomic profile and macronutrient content are highly conserved across mothers, and not influenced by maternal BMI. The systematic literature review indicated that milk leptin concentration is positively correlated with maternal BMI, whilst evidence pertaining to other hormones was either inconclusive or lacking. Of particular note in the metabonomic analyses were the diverse profiles observed of Human Milk Oligosaccharides secreted into mothers’ milk. These are genetically determined, and have developmental and protective effects for infants.

With regard to urinary metabolomic profiles, an association was observed between maternal BMI and maternal metabolome, but not infant urinary metabolome. Metabolites discriminating between mothers’ with different BMI were present across a range of chemical shifts, from the aromatic region associated with metabolites resulting from co-metabolism with the gut microbiota, to the aliphatic region.