Ward, Ellen
(2024)
Impact of Maternal Diet on Breast Milk Composition.
PhD thesis, University of Nottingham.
Abstract
Breast milk (BM) is natural biological fluid that contains many nutritive and protective components and breastfeeding (BF) is associated with improved health outcomes in infancy and reduced incidence of diseases such as obesity and hypertension later in life. The positive impact of BF on health and wellbeing is a result of the constituents within BM. BM is changeable in its composition, with certain components being more variable than others. This variability exists between and within mothers and is prompted by a multitude of factors, one of which is maternal diet. Certain dietary components have been reported to have strong associations with relative concentrations in BM, particularly fatty acids (FAs). Most of the research investigating the impact of maternal diet on BM, however, focuses on habitual intake effects and considerably less work has been done to explore acute changes in BM in response to maternal diet.
This thesis aims to address the above stated gap in the literature by assessing the acute impact of increasing sugar and fat consumption on BM composition, with a focus on macronutrients and certain metabolic hormones. A secondary aim of the thesis was to explore how BM composition naturally fluctuates over the course of a day. Additionally, to further understand the relationship between omega-3 FA intake and relative concentrations in BM, a systematic review investigating the influence of maternal omega-3 long chain polyunsaturated fatty acid (LCPUFA) intake via habitual diet/supplementation and their relative concentrations in milk was carried out.
To address the above concepts, a novel methodology was developed for more robust BM research. Initially, a proof-of-concept study within the UK was completed to test application of a dietary intervention alongside hourly BM sampling and laboratory methods. The data collected during the pilot study informed the design and conduct of a second larger study within Australia. Both trials delivered intervention diets containing relatively modest increases in sugar and fat to exclusively breastfeeding (EBF) mothers. BM samples were collected by mothers at hourly intervals alongside consumption of the study diets within their homes. BM lactose, glucose, protein, total fat/triacylglycerides, cholesterol and individual fatty acids were measured. The metabolic hormones leptin, adiponectin and insulin were also determined. Analyte concentrations were compared to determine the effects of an acute increase in sugar or fat on BM composition. The hourly samples were collected across 12 time-points, also enabling comparisons between time-points to detect any naturally occurring diurnal rhythms in BM components.
Responses to acute changes in maternal intake in BM macronutrients, hormones and FAs were detected in both studies. BM fats and FAs showed significant responses in both cohorts, whereas differing observations were identified for the remaining macronutrients. Total fat/triacylglycerides increased in response to the higher sugar intervention and triacylglycerides (TAGs) increased in response to the higher fat intervention employed in the pilot. The FA profile of BM was also responsive to the interventions. Specifically, total saturated FAs (SFAs) and polyunsaturated FAs (PUFAs) increased in response to the higher sugar diet whereas monounsaturated FAs (MUFAs) tended to decrease. In response to the higher fat diet there were increases in individual SFAs, MUFAs and PUFAs, however, total levels of these classes of FAs were unaffected. In the pilot study we observed some variations across the day in protein and lactose concentrations, however, these findings were not replicated in the second study. In the second study adiponectin and leptin concentrations decreased in response to the higher sugar intervention and leptin and insulin showed significant variations across the day. Further to the results of the feeding trials, a systematic review and meta-analysis of the literature concluded that there was a significant influence of maternal omega-3 LCPUFA intake from either food or dietary supplements on omega-3 concentrations in BM. Whilst, we noted an influence on BM FAs from maternal habitual FA intake, large amounts of heterogeneity interfered with the ability to collate conclusions from a large body of evidence and the systematic review contained only 8 studies.
The findings reported in this thesis support the hypothesis that maternal diet can acutely impact BM composition, and that fat and FA concentrations were particularly sensitive to these dietary changes. Further to this, we demonstrated that habitual FA intake influences the FA composition of human milk via a systematic review and meta-analysis. The acute influence of maternal diet on BM composition is a novel finding and assists in furthering BM research by delivering greater understanding into the dynamic nature of BM composition. The differences in analytes observed over the course of a day also assist in understanding the extent of variability in composition in individual women over the course of the day and should be considered in future when developing sample collection methodologies within BM compositional research.
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