Energy and macronutrient composition of banked donor human milk from a New Zealand milk bank : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand

Abstract

Background: Donor human milk (DHM) is the recommended alternative to commercial infant formula when an infant’s mother’s own milk is not available (Arslanoglu et al., 2013; Daniels et al., 2017; Meek & Noble, 2022). DHM use has been associated with reductions in the incidence and severity of prematurity-related morbidities, such as necrotizing enterocolitis (Miller et al., 2018). Although DHM is crucial for supporting the health of preterm infants, its macronutrient composition is known to vary significantly, posing challenges for fortification and clinical use (Perrin et al., 2020). Objective: Our aim was to understand the energy and macronutrient composition of DHM in New Zealand and contribute to the paucity of information which currently exists in the New Zealand context. Additionally, our study aimed to identify donor characteristics associated with DHM macronutrient composition. Methods: A secondary data analysis of 696 single-donor pools from 149 donors was conducted to describe the energy and macronutrient composition of DHM which had been donated to New Zealand’s first human milk bank in the Christchurch Women’s Hospital from July 2022 till July 2024. Single linear regression was performed in SPSS to explore the association between DHM macronutrients and the following variables: lactation stage, gestational age of the infant when the milk was expressed (i.e. preterm or term), donor age, and donor ethnicity. Results: DHM contained on average 74.9 kcal/100 mL energy; 4.0 g/100 mL fat; 1.2 g/100 mL true protein; and 8.1 g/100 mL total carbohydrate, consistent with published reference values for DHM. Mean true protein fell below the recommended intake for preterm infants, and mean energy was on the lower end of the recommended range. Mean fat and true protein varied considerably, with differences of 37.6-fold and 32.7-fold respectively. Gestational age and lactation stage were the strongest predictors of DHM macronutrient composition. There was also some suggestion of small differences due to donor age and ethnicity. Conclusion: There is a large variation in macronutrient composition between batches of DHM donated to the Christchurch Women’s Hospital Milk Bank, with some batches lacking adequate true protein and energy needed for optimal growth and development of vulnerable preterm infants. Our study highlights the need to explore the growth and health outcomes of the recipient infants and if this DHM variability has significant clinical implications.