Animal- and Plant-Source Protein-Rich Foods Differ in Their Association With Maternal Micronutrient Status and Breast Milk Composition During Lactation.

Micronutrient deficiencies in lactating women remain widespread and under-addressed, compromising maternal health and breast milk quality. Although dietary guidelines promote protein-rich foods, most do not distinguish between animal and plant sources within this food group, despite differences in nutrient profiles and bioavailability. This study examined associations between intake of animal-source and plant-source foods within the protein-rich food group and maternal nutritional biomarkers in blood and breast milk. Nutrient contributions from each source and intake patterns across sociodemographic groups were also assessed. Data were drawn from 220 mother-infant pairs in urban and rural West Java, Indonesia. Maternal dietary intake was assessed over 3 non-consecutive days using a combination of weighed food records and recall. At 5 months postpartum, maternal BMI, blood, and breast milk samples were collected to assess zinc, iron, vitamin A, and B12 status. Associations between dietary intake and maternal biomarkers were analysed using multiple linear regression, adjusting for relevant covariates. Total protein-rich food intake was not significantly associated with maternal biomarkers. However, higher intake of animal-source protein-rich foods was positively associated with serum B12 and zinc, while higher intake of plant-source protein-rich foods was inversely associated with breast milk vitamin A. Macronutrients, particularly protein and fat, from animal-based foods were more strongly associated with maternal micronutrient biomarkers than micronutrient intake alone. Protein-rich food intake did not vary across sociodemographic groups, indicating feasibility for broad-based interventions. These findings support a shift in dietary guidance for lactating women, from focusing solely on total quantity of protein-rich foods to recognising nutritionally meaningful differences between animal-source and plant-source foods.