Background

The significance of human milk in an infant's diet is well-established, yet there is a paucity of data on how much infants consume, particularly in later infancy (>6 months of age) when complementary foods are introduced. The objective was to estimate human milk intakes and total infant milk intakes (including infant formula) in New Zealand infants aged 7 to 10 months and explore factors that predict human milk intakes and total infant milk intakes.

Methods

First Foods New Zealand (FFNZ) study was a cross-sectional study investigating infant feeding practices in NZ, conducted between July 2020 and February 2022. Mother-infant dyads from two urban centres of NZ, who were breastfeeding, were included in a sub-study to investigate human milk intakes using the dose-to-mother stable isotope technique. Sociodemographic information was collected through questionnaires. Additionally, 24-hour recall data was collected to determine infant formula intake. Total infant milk intake in this study included all available data on milk feeding (human milk estimates and/or infant formula). Anthropometric measurements of both the infant and mother were collected following World Health Organization protocols.

Findings

FFNZ included 625 infants, with 171 participating in the breastfeeding sub-study. In total, 157 mother-infant dyads provided complete data for determining human milk volume. The mean (SD) human milk intake was 762 mL/day (256), higher in those consuming only human milk (804 mL/day), and decreasing with age. Total infant milk intakes were around 820 g/day, regardless of milk type. Factors predicting human milk intakes were infant age, BMI z-score, maternal education, employment status, maternal BMI, and demand or schedule feeding. Factors predicting total infant milk were infant age, sex, BMI z-score, caregiver education and infant morbidity Interpretation This study provides valuable insight into human milk intakes and total milk intakes during late infancy in New Zealand infants (7-10 months). The use of accurate assessment methods (dose-to-mother technique) enhances our understanding of infant milk intakes which contributes important knowledge in improving our ability to accurately assess nutritional intakes and nutrient adequacy of infants.