Extensive research shows that breast milk could have positive health effects not limited to infancy, but extend into childhood and adulthood. Recently many studies have provided new evidence on the long—term positive effects of breastfeeding, in particular protection against obesity and type 2 diabetes, suggesting that breast milk may have a role in the programming of later metabolic diseases. The mechanism throughout breastfeeding that exerts these effects has been a major focus of interest for researchers and it is still not completely known. There are some hints for biological plausibility of beneficial effects of breastfeeding including macronutrient intake, hormonal and behavioural mechanisms related to breast milk composition. Breast milk biochemical components, such as protein quantity and quality, polyunsaturated fatty acids, oligosaccharides, cytokines and hormones, in particular leptin, adiponectin and resistin together with the breastfeeding practice itself can influence infants feeding behaviour and regulation of growth and appetite control later in life. Further research is needed to confirm the possibility that hormones present in breast milk exert a metabolic and beneficial effects.