Litter Size Reduction as a Model of Overfeeding during Lactation and Its Consequences for the Development of Metabolic Diseases in the Offspring.

Overfeeding during lactation has a deleterious impact on the baby's health throughout life. In humans, early overnutrition has been associated with higher susceptibility to obesity and metabolic disorders in childhood and adulthood. In rodents, using a rodent litter size reduction model (small litter) to mimic early overfeeding, the same metabolic profile has been described. Therefore, the rodent small litter model is an efficient tool to investigate the adaptive mechanisms involved in obesogenesis. Besides central and metabolic dysfunctions, studies have pointed to the contribution of the endocrine system to the small litter phenotype. Hormones, especially leptin, insulin, and adrenal hormones, have been associated with satiety, glucose homeostasis, and adipogenesis, while hypothyroidism impairs energy metabolism, favoring obesity. Behavioral modifications, hepatic metabolism changes, and reproductive dysfunctions have also been reported. In this review, we update these findings, highlighting the interaction of early nutrition and the adaptive features of the endocrine system. We also report the sex-related differences and epigenetic mechanisms. This model highlights the intense plasticity during lactation triggering many adaptive responses, which are the basis of the developmental origins of health and disease (DOHaD) concept. Our review demonstrates the complexity of the adaptive mechanisms involved in the obesity phenotype promoted by early overnutrition, reinforcing the necessity of adequate nutritional habits during lactation.