Cancers are the leading cause of death worldwide, and various modalities of cancer treatment, such as surgery, radiation therapy, and pharmacological therapies, have been applied. Malnutrition and a loss of muscle mass are encountered frequently in cancer patients and adversely affect the clinical outcomes. Therefore, screening for, monitoring, and treating malnutrition are important procedures in treating cancer patients. This paper reviews the guidelines as well as comparative studies describing the nutritional support provided to cancer patients and describes the evidence-based guidelines and recommendation for each topic.