Distinct Nutrient Sources and Infant Outcomes: Impact of Breastmilk and Complementary Food on Indonesian Infant Growth and Micronutrient Status ^†

The relationship between infant nutrient intake and their nutritional status remains uncertain. Our previous study, which measured total intake from breastmilk (BM) and complementary food (CF), including infant formulas and cereal, found no significant association with growth and micronutrient status [1]. This study, conducted as part of an Indonesian breastfeeding cohort, aims to explore the relationship between intake from different sources, BM and CF, and nutritional outcomes, considering their differing nutrient profiles and bioavailability. Infant intake and growth were measured at 2 and 5 months of age, with iron (ferritin) and zinc (serum zinc) measured at 5 months. BM intake for energy was determined using creamatocrit analysis [2], while iron and zinc compositions were obtained by ICP-MS, then multiplied by individual milk volume measured by deuterium dose-to-mother [3]. CF intake was gathered by 3-day food records. Multivariable regression analysis was performed with intake as the predictor and growth and micronutrient biomarkers as the outcomes, adjusting for inflammation (CRP), breastfeeding practices (exclusive/partial), location (urban/rural), maternal age, and infant sex. Among 221 infants, mean anthropometric status at 5 months was low, with a height-for-age z-score (HAZ) of −0.8 (0.9), weight-for-age z-score (WAZ) of −0.6 (0.9), and weight-for-height z-score (WHZ) of 0.0 (1.0). The mean ferritin level was 35.9 ± 29.7 µg/L, and the mean zinc level was 10.4 ± 1.3 µmol/L. In partially breastfed infants, CF contributed 38% of total energy intake, 90% of iron intake, and 62% of zinc intake. Multivariable analysis revealed that only energy intake from BM was positively and significantly associated with infant growth, with every 100 kcal increase in BM energy associated with increases of 0.382 in HAZ (p < 0.001), 0.539 in WAZ (p < 0.001), and 0.383 in WHZ (p < 0.001). No correlation was observed between iron intake from either BM or CF with ferritin status at 5 months, but a positive correlation was found between zinc intake from BM and zinc status, with a 1.4 increase per mg of zinc intake (p = 0.001). No such correlation was observed with CF zinc intake and zinc status. These findings were consistent for intake at both 2 and 5 months in relation to growth, iron, and zinc status. The lack of association between total infant diet and outcomes might be explained by differences in nutrient profiles from breastmilk and non-breastmilk sources. Analysing them separately could help clarify the association between dietary intake and infant outcomes. Monitoring BM composition as well as encouraging and supporting breastfeeding are crucial due to its potential to enhance infant nutrition.