Purpose of review To update the healthcare providers on the potential contribution of increased basal metabolic rate, hypermetabolism, and low testosterone in the development of weight loss in cancer patients. Recent findings Cancer cachexia, the loss of skeletal muscle with or without the loss of fat, is a multifactorial syndrome. A wide variation in the frequency of hypermetabolism exists in cancer patients and can only be accurately identified by an indirect calorimeter. The frequency of hypermetabolism increases depending on the histology and stage of tumor, associated with the presence of an acute inflammatory response, and is often accompanied by weight loss. Hypogonadism, as a result of chemotherapy, radiation treatment, or the use of opioids to treat chronic pain, is frequently noted in male cancer patients and has been reported to be also associated with anorexia and weight loss. Summary Cancer patients may develop weight loss, cachexia, which can be distressing for both patients and their family. Treatments directed at reducing the basal metabolic rate and supplementation of testosterone in hypogonadic male patients may have the potential to improve lean body mass, but more research is needed.