Leptin is a natural component of breast milk (Casabiell et al., 1997), and is considered an essential nutrient during lactation in protecting against the development of obesity and associated pathologies in adulthood (Pico et al., 2007; Sanchez et al., 2008; Palou and Pico, 2009). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.