Objective To explore the correlation between the body composition and breast milk nutritional components in overweight/obese mothers, and to analyze their impact on infant physical growth, thereby providing scientific evidence for nutritional interventions during breastfeeding.

Methods A prospective cohort study was conducted. Women who delivered at Suzhou Municipal Hospital affiliated with Nanjing Medical University between October 2022 and June 2023 and their infants were randomly selected 42 days postpartum. A total of 114 overweight/obese women (66 overweight and 48 obese) and their infants were included as the overweight/obese group, while 132 women with normal body mass index (BMI) and their infants were included as the control group. Baseline data were collected at enrollment, and the mothers’ body composition and breast milk nutritional were analyzed, and the infants’ physical measurements were conducted. Infant growth was observed longitudinally until 3 months of age.

Results Pearson correlation analysis showed that the protein energy ratio of breast milk from mothers in the overweight/obese group was lower than that in the control group, while the fat energy ratio was higher (P < 0.05). In the overweight/obese group, fat-free mass index (FFMI) and skeletal muscle index (SMI) of the mothers were positively correlated with breast milk fat content, whereas fat mass index (FMI) and percentage of body fat (PBF) were negatively correlated with total energy, fat, and protein content in breast milk (P < 0.05). In the control group, FFMI was positively correlated with breast milk fat (P < 0.05). The SMI of mothers in the overweight/obese group and FFMI of mothers in the control group were positively correlated with the weight gain of infants from 42 days to 3 months of age (P < 0.05). There was no statistically significant correlation between FMI, PBF, and infants’ growth velocity (P > 0.05).

Conclusion Maternal fat-free mass plays a crucial role in influencing the nutritional components of breast milk and early infant growth, while excessively high body fat percentage in overweight/obese mothers may adversely affect breast milk quality. Further in-depth research is needed to explore this issue.