Maternal Adiposity, Milk Production and Removal, and Infant Milk Intake During Established Lactation

Background: Whilst maternal body mass index (BMI) is linked to suboptimal breastfeeding outcomes, maternal body composition has not been assessed with respect to milk production (MP). Methods: Lactating mothers 1–6 months postpartum (n = 281) completed a demographic questionnaire and a 24 h MP measurement using the test-weigh method, enabling the calculation of 24 h MP parameters, breast storage capacity (BSC) and the percentage of available milk removed (PAMR). Body composition was measured with bioimpedance spectroscopy. Linear regression models were used to determine maternal and infant factors associated with MP parameters; structural equation modelling was used to assess the mediating role of BSC. Results: Higher maternal adiposity was associated with lower BSC (p ≤ 0.028), MP (p ≤ 0.003), infant breast milk intake (p ≤ 0.003) and total milk intake (p ≤ 0.026). Higher BSC was associated with higher MP (p < 0.001), with BSC confirmed as a mediator of the relationship between adiposity and MP (67.5%). Mean PAMR was negatively associated with BSC and milk removal frequency (both p < 0.001), and was lower in occasionally pumping compared to breastfeeding only (p = 0.037) and exclusively pumping mothers (p = 0.012). Conclusions: Our findings confirm maternal adiposity as a major contributor to low MP and reveal BSC, which is a measure of glandular tissue volume or breast development, as a mediator between adiposity and MP. This provides a rationale for antenatal lactation assessment of mothers and timely intervention in high-risk mothers to ensure they reach their full lactation potential.