The invention relates to novel methods and compositions for safely reducing negative side effects of cancer treatments. These methods and compositions comprise administering to a patient a composition comprising one or more of the following: curcumin (derived from turmeric), epigallocatechin-3-gallate (EGCG, enriched in green tea), glucosinolates (enriched in cruciferous vegetables) and / or derivatives thereof, such as sulforaphane (SFN), alone or combined with a ketogenic diet or a modified ketogenic diet. Also the current invention relates to a composition comprising medium chain triglycerides (MCT), Epigallocatechin-3-gallate, curcumin, compositions comprising glucosinolates and / or derivatives thereof, such as sulforaphane (SFN). The invention provides that administering a composition comprising curcumin, EGCG, sulforaphane, alone or combined with a ketogenic diet or a modified ketogenic diet (low carbohydrate diet) alone or supplemented with MCT improves resistance of normal cells to cytotoxicity of cancer treatments, in turn, reducing their negative side effects. Increasing normal cells, tissues or organs' resistance to chemotherapeutic agents, the invention improves patients' tolerance to anti-cancer treatments' toxicity, which, in turn, contributes to enhance their efficacy, leading to increased survival of the subject treated with the current invention.