Background: Beside the classical anticancer treatment tumor patients try to find proactive alternative therapies to fight their disease. Lifestyle changes such as introducing a ketogenic diet is one of the most popular among them. The German Association of Urological Oncology (AUO, Arbeitsgemeinschaft Urologische Onkologie) presents a systematic review investigating the evidence of ketogenic diet in cancer patients. Materials and methods: A systematic literature research was conducted in the databases Medline, Livivo, and the Cochrane Library. Only clinical studies of tumor patients receiving chemotherapy while on a ketogenic diet were included. The assessment of the results was performed according to the predefined primary endpoints overall survival and progression-free survival and secondary endpoints quality of life and reduction of adverse effects induced by cytostatics. Results: Nine studies met the inclusion criteria: eight prospective and one retrospective study case series respectively cohort-studies, with a total of 107 patients. Currently there is no evidence of a therapeutic effect of a ketogenic diet in patients with malignant tumors regarding the clinical outcome or quality of life. Conclusion: Based on the current data, a ketogenic diet can not be recommended to cancer patients because prospective, randomized trials are missing.