Cancer, one of the leading causes of human death worldwide, is conventionally treated through approaches including surgery, radiotherapy, and chemotherapy. However, conventional therapeutic approaches for cancer exhibit distinct limitations, necessitating an urgent need for effective and safe therapeutic or adjuvant strategies in clinical practice. The ketogenic diet (KD), as a low-carbohydrate and high-fat diet, can utilize the tumor’s distinct characteristics of metabolic reprogramming to restrict the energy source of tumor cells. In this article, we review the feasibility of KD in tumor treatment, its anti-tumor efficacy when applied either independently or as an adjuvant therapy, and the underlying mechanisms, providing a theoretical foundation for the clinical application of KD in cancer treatment.