IntroductionThe role of perinatal diet in postpartum maternal mood disorders, including depression and anxiety, remains unclear. We investigated whether perinatal consumption of a Western‐type diet (high in fat and branched‐chain amino acids [BCAA]) and associated gestational weight gain (GWG) cause serotonin dysregulation in the central nervous system (CNS), resulting in postpartum depression and anxiety (PPD/A).MethodsMouse dams were fed one of four diets (high‐fat/high BCAA, low‐fat/high BCAA, high‐fat, and low‐fat) prior to mating and throughout gestation and lactation. Postpartum behavioral assessments were conducted, and plasma and brain tissues assayed. To evaluate potential clinical utility, we conducted preliminary human studies using data from an extant sample of 17 primiparous women with high GWG, comparing across self‐reported postpartum mood symptoms using the Edinburgh Postnatal Depression Scale (EPDS) for percent GWG and plasma amino acid levels.ResultsMouse dams fed the high‐fat/high BCAA diet gained more weight per kcal consumed, and BCAA‐supplemented dams lost weight more slowly postpartum. Dams on BCAA‐supplemented diets exhibited increased PPD/A‐like behavior, decreased dopaminergic function, and decreased plasma tyrosine and histidine levels when assessed on postnatal day (P)8. Preliminary human data showed that GWG accounted for 29% of the variance in EPDS scores. Histidine was also lower in women with higher EPDS scores.ConclusionsThese findings highlight the role of perinatal diet and excess GWG in the development of postpartum mood disorders.