1. Introduction
Human milk is recognized as the best food for newborns, rich in lipids, proteins, carbohydrates, and other micronutrients to ensure the enough energy and nutrients for newborns for growth and development (Harding et al., 2017). The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months of life of infants (Eidelman et al., 2012). Lipids are important nutrients in breast milk, accounting for about 3-5% and providing 50-60% of the newborn’s energy (Demmelmair and Koletzko, 2018). Human milk lipids are reported as variable influenced by many factors for example individuals, lactational period, maternal dietary etc (Grunewald et al., 2019; Burianova et al., 2019; Gridneva et al., 2022; Ye et al., 2021).
The fatty acid (FAs) profiles in human breast milk have been well-studied worldwide (Liu et al., 2018). Recent studies show that triacylglycerols (TAGs) in human breast milk have unique molecular structure and showing important roles for infant lipid digestion and metabolism. Previously, we analyzed the TAG composition of Chinese human milk, found a group of TAG containing both medium-chain fatty acids (MCFAs) and long-chain fatty acids (LCFAs) esterified at one glycerol backbone, namely medium- and long-chain triacylglycerol (MLCT) (Yuan et al., 2020). According to the number of medium-chain fatty acid (MCFA) and long-chain fatty acids (LCFAs) on the glycerol backbone, MLCT can be divided into two types,the MLCT esterified with one MCFA and two LCFAs are the MLL type; and the MLCT esterified with two MCFAs and one LCFA are the MML type. In human milk, MLCT types of TAGs contains approximately 40 kinds of TAGs, accounting for 20-30% of total TAG (Zhang et al., 2021; Yuan et al., 2021). There are obvious differences of the MLCT content and molecular species in lipids between human milk.
Compared with LCT, MLCT has not only long-chain fatty acids, but also medium-chain fatty acids. Due to the presence of MCFA, it is more conducive to the direct absorption and utilization of infants, MLCT will have higher lipolysis degree as well as release higher levels of free fatty acid in infant intestinal digestion (Yuan et al., 2020; Wang et al., 2022), therefore MLCT is conducive to the digestion and absorption of lipids, providing fast energy (Yu et al., 2022a). In addition, MLCT has more incorporation of long-chain fatty acids than MCT, allowing it to provide the physiological activities of the body (Lee et al., 2022).
Previous studies show that FAs in human milk are highly influenced by the maternal diet (Ward et al., 2021; Wang et al., 2010). The content of protein, and lactose in breast milk was not obviously affected by the breast milk diet, but the fatty acids in breast milk were affected by the mother ’s immediate diet (Aumeistere et al., 2019). There are also studies of Nigeri mothers that high carbohydrate intake leads to higher MCFA in breast milk, while excessive intake of fat may lead to lower levels of MCFA (VanderJagt et al., 2000), Sudan (Nyuar et al., 2010), and Egypt (Bakry et al., 2021) show high content of 12:0 and 14:0, which were approximately 20% of total fatty acids. Current studies have shown that MCFAs are affected by dietary structure, but the relationship between TAG containing MCFAS and dietary patterns in breast milk is rarely studied.
This study aims to analysis the correlation between MLCT content & molecular species and maternal dietary patterns. This study collected mature breast milk samples and dietary intake data of healthy Chinese lactating women 30-90 days postpartum . A total of 180 volunteer mothers were divided into three groups fat group (> 30 energy %, n = 60), carbohydrate group (> 50 energy %, n = 60), and protein group (>15 energy %,n = 60) according to Yang (Yang, 2018). recommendations. TAGs were identified and quantified using High Performance Liquid Chromatography-Mass Spectrometry (LC-MS) following our previous studies. The composition of MLCTs in breast milk and their relationship with nutrient energy supply ratio were clarified, which provided scientific basis for developing novel structured lipids used in infant formula.