In the present observational study, research is focused on breast milk in northwestern Spain, more precisely Galicia. In this context, the obtained data will serve to define the nutritional characteristics of breast milk from Galician women (interindividual variation), while at the same time evaluating the existence of specific features related to their particular diet (dietary factors), the Southern European Atlantic Diet (SEAD). All the variables measured in this research project will be related with breast milk composition. Expected primary outcomes can be divided as follows: fatty acid profiles, mineral composition, essential amino acid profiles, microbiota and steroid hormones. The key influencing factors taken into account are: lactation characteristics and maternal diet.