Fasting concomitantly with oncology treatments (chemotherapy mainly) induces a growing interest among patients following overmediatisation of recent discoveries. The goal of this article is to provide updated information about this approach. According to preclinical studies, fasting may be a way to increase the therapeutic index of major oncology treatments. However, clinical data is based on small exploratory studies only and the results of larger scale studies are not yet available. The approach of fasting during chemotherapy can and should neither be recommended nor implemented in standard care. However, further scientific and clinical investigation may contribute to a better understanding of the metabolic aspects of cancer.