BACKGROUND Our study aims to investigate the role of segmental multi-frequency bioelectrical impedance analysis (SMF-BIA) in the monitoring of upper limb water changes of patients with breast cancer before and after surgery to aid in establishing a new approach to preventing lymphedema. MATERIAL AND METHODS This study included 442 female patients with breast cancer. We used SMF-BIA to monitor changes in body composition. Data were collected 1 day before surgery and 7 days and 3 months after surgery. RESULTS The average body mass index (BMI) of patients was normal but, in 22.8% of patients, the percentage of body fat exceeded the average, which is known as invisible obesity. Moreover, the weight, BMI, basal metabolic rate, inorganic salt content, muscle content, total body water, and extracellular water of patients increased 7 days after surgery (P
