Pain caused by the tumor can result in severe anorexia and a decrease in the amount of foods and liquids consumed. Changes in the body's metabolism can also cause nutritional problems. Tumor cells often convert nutrients to energy in different, less efficient ways than do other cells. Tumors may produce chemicals or other products that can cause anorexia and cachexia. For example, tumors can produce a substance that changes a person's sense of taste, so that the patient does not want to eat.
Tumors can affect the receptors in the brain that tell the stomach if it is full.
Tumors can also produce hormone substances, which can change the amount of nutrients eaten, the way they are absorbed, and the way they are used by the body.