Abstract
Breastfeeding provides all the energy that the child needs in the form of nutrients in the first months of life. The components cover the nutritional needs in all stages, including colostrum and final or mature milk. It must also be taken into account that the composition of milk varies from one woman to another, between both breasts, between feedings and in the different stages in the same mother. It can be said that variation is an active mechanism to perfectly adjust to the nutritional and immunological needs of each child. Components of breast milk can exert beneficial non-nutritional functions. Breast milk also has bioactive factors, which affect biological processes and, therefore, have an impact on health. In the nutrition of premature babies, parenteral nutrition is carried out first, which later becomes enteral through different strategies, such as early minimal enteral nutrition. Despite this, they still present postnatal growth restrictions, which is associated with adverse neurocognitive outcomes. Breast milk achieves multiple benefits in both preterm and term births. Digestion and absorption in the stomach and intestines follow circadian rhythms in mammals, and these rhythms are regulated by rhythmically expressed clock genes in the intestine, as well as by daily food intake.