Background and aim: Breastfeeding (BF) is a protective factor against childhood obesity; however, the mechanisms associated with this effect have not yet been elucidated. This study aimed to describe the mechanisms related to the protective effect of breastfeeding against childhood obesity. Methods: A search on PUBMED, SCOPUS, Cochrane Library and SCIELO databases was carried out to develop a descriptive review of the scientific evidence. The key words were breastfeeding; obesity; mechanism and diet. Articles were reviewed in Spanish and English from 1977 to 2020. Results: The protective effect of BF against childhood obesity is given by a combination of several mechanism. Its nutritional composition and the contribution of bioactive substances stand out, some of them regulated by the energy intake. Infants who are breastfed choose healthier foods in preschool, regardless of sociodemographic factors. Effects on adiposity, control of body weight and energy intake have also been described by epigenetic regulation programming and the intestinal microbiota. Conclusion: BF is a unique process that interacts in a complex way with infants and preschoolers' growth and developmental factors Its protective role against childhood obesity has been associated with various mechanisms. New research is still required to understand the implications of BF in pediatric age and its role in preventing obesity.