Cancer patients often experience significant weight loss due to metabolic changes, increased resting energy expenditure (REE), and poor nutrient intake, particularly exacerbated by treatments like chemotherapy and radiation. This study aimed to determine whether combining Oral Nutrition Supplements (ONS) with dietary education is more effective than dietary education alone in improving nutritional outcomes for cancer patients. An open-label randomized clinical trial at Persahabatan Hospital in Jakarta, Indonesia, involved 108 patients with lung or gynecological cancer, with 87 completing the study. Participants were assigned to receive either dietary education plus ONS (intervention group) or dietary education alone (control group). Results indicated that while both groups improved their nutrition knowledge, the intervention group experienced significant increases in body weight (1.68 ± 3.96 kg) and body mass index (BMI) (0.86 ± 1.96 kg/m2), whereas the control group lost weight. Additionally, the intervention group had a lower rate of anemia (60% vs. 80.9%), though no significant differences were found in albumin levels or inflammation status. These findings suggest that ONS combined with dietary education may help improve weight and BMI in cancer patients, warranting further research to confirm these benefits and assess long-term effects. © 2025 Taylor & Francis Group, LLC.