Cancer is a disease that can appear in several tissues and that kills more than 150 000 people in France every year. Cancer cells have mutations in their genome that lead to changes in their metabolism, compared to healthy cells. They use mostly glycolysis as their energy source, but not fatty acid oxidation. Currently, treatments used against cancer are nonspecific and have many side effects. Thus it appears increasingly important to find new strategies against cancer cells progression while protecting surrounding healthy cells and decreasing side effects. Ketogenic diet, which is a low-sugar high-fat diet, could be an interesting candidate as it alters the energy machinery of the cell and keeps away its primary energy source (glucose). This diet is largely used to treat refractory epilepsy and begins to be studied in oncology as well. This article describes the scientific evidence of the beneficial effects of the ketogenic diet and aims at showing how this complementary treatment could be useful against several cancers.