Macronutrient content and fatty acid composition and their positional distribution in human breast milk from Zhejiang Province, China in different lactation periods.

Lactational changes in macronutrient content, lipid profile, fatty acid composition, and positional distribution of human breast milk were investigated in this study. A total of 378 milk samples of six different lactation periods, including 0‒5, 6‒14, 15‒30, 31‒90, 91‒180, and 181‒360 days, were collected cross-sectionally from healthy lactating women in Zhejiang, China. As lactation progressed from 0‒5 to 15‒30 days, the lipid content and the percentages of C10:0, C12:0, C14:0, C18:2-6, and C18:3-3 increased significantly, while the protein concentration and the proportions of phospholipids, cholesterols, C16:0, C18:1-9, C24:1-9, C20:4-6, C22:4-6, C22:5-3, and C22:6-3 decreased notably. When lactation was further extended to 181‒360 days, the protein content continued to decrease, and the percentages of C12:0 and C14:0 continued to increase, whereas the levels of other tested nutrients remained stable. Although the triacylglycerol positional distributions of some fatty acids underwent significant lactational variations, C14:0, C16:0, C24:1-9, C22:4-6, C22:5-3, and C22:6-3 were located mainly at the -2 position, while C18:1-9, C18:2-6, and C18:3-3 were primarily distributed at the -1,3 positions. Compared with human breast milk reported in Western countries, samples in our study demonstrated higher percentages of C18:2-6, C18:3-3, C20:4-6, and C22:6-3, but lower proportions of C12:0, C14:0, and C18:1-9. The results from this study indicated a nutritional composition different from that of the Western countries and may provide useful data for the development of infant formulas closer to Chinese breast milk in terms of the fatty acid composition and its specified positional distribution on triglyceride structure.