Weight loss and muscle wasting commonly occurs in patients with cancer, negatively influencing their quality of life, treatment response and survival. Weight loss has been reported as a side effect of chemotherapy treatment in cancer. Weight changes may be the consequence of energy imbalance and disturbances in protein metabolism (through different factors linked with chemotherapy), such as reduced caloric and protein intake (partly related to depression), poor treatment tolerance, hormonal alterations, systemic inflammation etc. This results in body composition modiﬁcations in favor of fat gain and/or lean body mass loss in early stage cancer and loss of both fat mass and lean mass in advanced cancer. Depletion of lean tissue in cancer patients is related to short survival, and decreased skeletal muscle mass and function may result in fatigue and inactivity, which contributes to fat mass changes and can be responsible for chemo-toxicity and increased mortality.