Rationale and objectiveSchizophrenia displays sex differences in many aspects. Decreased brain-derived neurotrophic factor (BDNF) levels have been reported to be associated with high body weight or obesity as well as other psychopathological aspects in schizophrenia patients. This study aimed to explore sex differences in the relationship between serum BDNF levels and obesity in patients with chronic schizophrenia.MethodsWe recruited 132 Chinese patients with chronic schizophrenia (98 males and 34 females) and compared sex differences in the body mass index (BMI), obesity, serum BDNF levels, and their associations. Psychopathology symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). A regression model with various demographic and clinical variables was applied to predict the serum levels of BDNF.ResultsFemale patients had a higher rate of obesity and higher BMI, but lower BDNF levels than male schizophreniapatients. A significantly negative correlation was observed between BMI and BDNF levels only in female patients but not in male patients. The multiple regression model with demographic and clinical variables significantly predicted BDNF levels only in female patients, with a medium size effect. And only in female patients, BMI made a significant contribution to this prediction.ConclusionOur results indicate significant sex differences in the obesity, BMI, BDNF levels, and their association in chronic patients with schizophrenia, showing a significant inverse correlation between BMI and BDNF levels only in female patients. Thus, sex needs to be considered when assessing the relationship between BDNF and metabolic syndromes in schizophrenia.