Cancer cachexia is a complex multi-organ syndrome characterized by weight loss, muscle atrophy and fat mass loss. With a prevalence of 1 million people in Europe and only limited therapeutic options, there is a high medical need for new approaches to treat cachexia. In this context, we started a few years ago studying the therapeutic interest of modulating the gut microbiota in the context of cancer cachexia. We discovered not only that the gut microbiota composition and function were deeply altered in cancer cachexia but also that the gut function itself was altered at several levels, independently of any chemotherapeutic intervention. Furthermore, our experimental results establish that nutritional modulation of the gut microbiota using prebiotics and/or probiotics could constitute an interesting adjuvant therapeutic tool for cancer and associated cachexia.