Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 54 8 2025 09 02 1701 1711 Marziyeh Ghalamkari Hematologist and Medical Oncologist, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Leyla Sahebi Maternal, Fetal and Neonatal Research Center, Family Health Research Institute, Tehran University of Medical Sciences, Teh-ran, Iran Sara Toogeh Thrombosis Hemostasis Research Center, Tehran University of Medical Sciences, Tehran, Iran Gholamreza Toogeh 1. Thrombosis Hemostasis Research Center, Tehran University of Medical Sciences, Tehran, Iran 2. Division of Clinical Hematology Oncology and Bone Marrow Transplantation, Vali-e-Asr Hospital, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran 2025 01 29 2025 04 23 Background: We evaluated the effects of fasting on cancer treatment outcomes, gathering evidence separately from human clinical trials and in vitro (animal) studies. Methods: A comprehensive search was conducted using the PubMed, Scopus, and Web of Science databases. Studies were included if they examined the effects of fasting on cancer treatment outcomes in vitro or in human subjects, regardless of study design, sample size, or country of origin. Results: A total of 16 studies were included, consisting of 6 in vitro and animal studies and 10 human clinical trials. In vitro and animal studies consistently showed that fasting enhances the efficacy of chemotherapy and reduces its toxic side effects. Human clinical trials indicated that short-term fasting could decrease chemotherapy-induced side effects such as nausea, fatigue, and immunosuppression while improving overall response rates. However, the number of clinical trials is limited, and there is significant variability in study designs, fasting protocols, and endpoints. Conclusion: Fasting may serve as a beneficial adjunct to cancer therapy, particularly in mitigating chemotherapy-induced side effects and enhancing treatment efficacy. Despite these promising results, further large-scale, well-designed clinical trials are necessary to confirm these findings and establish standardized fasting protocols. Future research should also investigate the long-term effects of fasting and its impact on different cancer types and treatment modalities. While some patients may fast without significant adverse effects, the primary concern should always be their safety and well-being. https://ijph.tums.ac.ir/index.php/ijph/article/view/38006 https://ijph.tums.ac.ir/index.php/ijph/article/download/38006/8625