Resilience of Breastmilk Composition to Maternal Nutritional Stress in Mothers with Preterm Infants

<b><i>Background:</i></b> Preterm infants experience increased oxidative stress and possess limited endogenous antioxidant reserves. Breastmilk provides critical protection, but its composition under maternal nutritional stress remains poorly characterized. <b><i>Objectives:</i></b> To evaluate the nutritional and antioxidant profile of colostrum and mature milk from mothers with preterm births and under nutritional stress. <b><i>Methods:</i></b> Breastfeeding mothers from Veracruz, México, who delivered preterm infants were recruited. Dietary intake was evaluated using a food frequency questionnaire. From the total cohort (<i>n</i> = 42), a subset of mothers (<i>n</i> = 32) provided colostrum and mature milk samples which were analyzed for total proteins, total polyphenols, and antioxidant capacity using 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays. Associations with maternal body mass index, dietary intake, gestational age, and socioeconomic status were examined. <b><i>Results:</i></b> Mothers experienced nutritional stress, with low diversity, energy dense, and nutrient-poor dietary pattern dominated by consumption of ultra-processed foods. Despite this, breastmilk retained adequate levels of protein, polyphenols, and antioxidant capacity in both colostrum and mature milk. <b><i>Conclusion:</i></b> Even under maternal nutritional stress, breastmilk composition remained functionally resilient, delivering adequate levels of nutritional and antioxidant components, sufficient to meet the elevated demands of preterm infants.