Evolution of energy composition, fatty acids and immunological factors (TNF-α and IL-10) in transitional human milk during a single breastfeeding session

This study aimed to evaluate the influence of different time points within a single breastfeeding session, including foremilk (0–1 min, T1), middlemilk (15 min, T2), and hindmilk (30 min, T3), on energy content, fatty acid composition, and the concentrations of the tumor necrosis factor-alpha (TNF-α) and interleukin-10 (IL-10) in transitional human milk. This descriptive case-series study involved five lactating mothers (M1-M5), whose samples were analyzed for energy content using crematocrit, fatty acids by gas chromatography, and cytokines (IL-10 and TNF-α) by immunoassays. An exploratory principal component analysis (PCA) was also performed to assess relationships among the variables. Among the results, a progressive increase in energy content was observed throughout breastfeeding, except in M2 and M4, where an increase occurred only in T3. The fatty acid composition illustrated by the heat map highlighted palmitic (16:0), oleic (18:1n-9), and linoleic (18:2n-6) acids as the most abundant, representing the main classes of saturated, monounsaturated, and polyunsaturated fatty acids, respectively. TNF-α and IL-10 levels remained stable throughout breastfeeding, except in M1 and M3, which showed increased cytokines levels at T3. PCA revealed distinct maternal patterns among the mothers evaluated, indicating intra-individual consistency and individualized lactation profiles. Although the small sample size and lack of detailed maternal baseline characteristics limit definitive conclusions, the findings suggest that variations in transitional human milk composition may be driven more by maternal individuality than by temporal changes within a single breastfeeding session. Further studies with larger cohorts and better control of maternal variables are needed to clarify these relationships.