Background: Cancer and its treatment affect the patient's nutritional status. Weight loss and changes in body composition following chemotherapy may affect clinical outcomes.

Objective: The study aimed to investigate changes in body weight and body composition in Moroccan cancer patients after the first cycle of neoadjuvant chemotherapy (NAC).

Methods: This prospective study included 139 cancer patients. Anthropometric measurements were performed using standardized equipment. Bioelectrical impedance analysis was used to assess body composition. Clinical data are taken from the hospital database.

Results: body mass index (BMI) and fat-free mass values decreased significantly four weeks after receiving neoadjuvant chemotherapy (NAC), while fat mass and body fat percentage increased significantly. The proportion of patients with low BMI, reduced muscle mass, and sarcopenic obesity also significantly increased (9.4% vs. 11.5%, 16.7% vs. 33.3%, and 5.0% vs. 21.7%, respectively). Approximately, 62% of patients experienced weight loss. Men were significantly more likely than women to have reduced muscle mass. Non-overweight patients had higher odds of losing weight and muscle mass than their overweight-obese counterparts. Similarly, colorectal cancer patients were 2.14 times more likely to experience moderate/severe weight loss than other patients. However, women with breast or uterine cancer were less likely to have reduced muscle mass than patients with other cancer types.