Anorexia, the loss of appetite or desire to eat, is typically present in 15% to 25% of all cancer patients at diagnosis and may also occur as a side effect of treatments. Anorexia is an almost universal side effect in individuals with widely metastatic disease [10,11] because of physiologic alterations in metabolism during carcinogenesis. (Refer to the Tumor-induced Effects on Nutritional Status section.) Anorexia can be exacerbated by chemotherapy and radiation therapy side effects such as taste and smell changes, nausea, and vomiting. Surgical procedures, including esophagectomy and gastrectomy, may produce early satiety, a premature feeling of fullness. Depression, loss of personal interests or hope, and anxious thoughts may be enough to bring about anorexia and result in PCM. Evidence-based recommendations have been published describing various approaches to the problems of cancer-related fatigue, anorexia, depression, and dyspnea. Other systemic or local effects of cancer or its treatment that may affect nutritional status include hypermetabolism, sepsis, malabsorption, and obstructions.
Anorexia can hasten the course of cachexia, a progressive wasting syndrome evidenced by weakness and a marked and progressive loss of body weight, fat, and muscle. Cachexia is estimated to be the immediate cause of death in 20% to 40% of cancer patients; it can develop in individuals who appear to be eating adequate calories and protein but have primary cachexia whereby tumor-related factors prevent maintenance of fat and muscle. Particularly at risk are patients with diseases of the gastrointestinal tract.
The etiology of cancer cachexia is not entirely understood. Cachexia can manifest in individuals with metastatic cancer as well as in individuals with localized disease. Several theories suggest that cachexia is caused by a complex mix of variables, including tumor-produced factors and metabolic abnormalities. The basal metabolic rate in cachectic individuals is not adaptive, that is, it may be increased, decreased, or normal. Some individuals do respond to nutrition therapy, but most will not see a complete reversal of the syndrome, even with aggressive therapy. Thus, the most prudent and advantageous approach to cachexia is the prevention of its initiation through nutrition monitoring and nutrition intervention.