During lactation, obesity is associated with reduced PRL action since the obese condition lowers the expression of PRL receptors (PRLRs) in mammary epithelial cells, hindering PRL signaling and causing a reduction in the production of milk components such as β–casein and α–lactalbumin, leading to lactation insufficiency and precocious mammary gland involution [9]. This evidence concerns the gene PRL and obesity due to melanocortin 4 receptor deficiency.