Short-term starvation (or fasting) protects normal cells, mice, and potentially humans from the harmful side effects of a variety of chemotherapy drugs. Here we show that treatment with starvation conditions sensitised yeast cells (S. cerevisiae) expressing the oncogene-like RAS2val19 to oxidative stress and 15 of 17 mammalian cancer cell lines to chemotherapeutic agents. Cycles of starvation were as effective as chemotherapeutic agents in delaying progression of specific tumours and increased the effectiveness of these drugs against melanoma, glioma, and breast cancer cells. In mouse models of neuroblastoma, fasting cycles plus chemotherapy drugs—but not either treatment alone—resulted in long-term cancer-free survival. In 4T1 breast cancer cells, short-term starvation resulted in increased phosphorylation of the stress-sensitising AKT and S6 kinases, increased oxidative stress, caspase-3 cleavage, DNA damage and apoptosis. These studies suggest that multiple cycles of fasting promote differential stress sensitisation in a wide range of tumours and could potentially replace or augment the efficacy of certain toxic chemotherapy.