The study looked at how the weight gain during pregnancy, certain sugars in breast milk, and the types of bacteria in breast milk are connected in healthy mothers from Northwest China. Most mothers were found to have a gene that makes specific sugars in breast milk. These sugars varied between mothers with the gene and those without. Mothers who gained weight normally during pregnancy had more diverse bacteria in their breast milk, including helpful types like Bifidobacterium and Lactobacillus. This research helps in creating personalized nutrition guidelines for mothers.