Objective: The relationship between leptin in human milk (HM) and infant growth is quite controversial. The aim of the present study was to review the epidemiological literature currently available on the relation between the appetite-regulating hormone leptin in HM with growth and infant weight gain. Also, to know if it influences on the center of satiety of the infant, and if this hormone has an effect in the self-regulation of food intake. Methods: A review of review and original research articles published from January 1, 2015 up to December 31, 2019 measuring leptin in HM and infant weight gain was performed in the PubMed and Embase databases. The literature showed a total of 237 articles, where the title and abstract were evaluated to eliminate duplicate citations and later exclusion criteria were established to discard articles. Eighteen articles met the inclusion criteria. Results: Six articles showed a relationship between leptin present in HM and infant weight. Five articles reported on leptin in HM and the effect on satiety and self-regulation of infant intake. Studies of leptin in infant serum blood were quite controversial. There is an inverse relationship between the leptin in HM and infant weight gain. Also, breastfed infants better self-regulate their intake and have a better relationship with food. The duration of breastfeeding directly influences on the growth of the infant due to the hormones present in the milk. However, these mechanisms are unclear, and the results are controversial. Conclusion: The evidence from the studies allowed us to establish that there is an association between leptin in HM and infant weight gain. However, there is still a lack of longitudinal studies, with a larger number of participants and well-established inclusion criteria about the relationship between leptin in HM exposure and the development of infant weight gain.
Keywords: appetite-regulating hormone; breast milk; breastfeeding; human milk; leptin; obesity.