As an oncology expert with extensive experience in cancer treatment and its side effects, I can explain why patients undergoing chemotherapy often experience weight loss. Chemotherapy is a treatment that uses strong drugs to kill cancer cells. However, these drugs can also affect healthy cells in the body, leading to various side effects. One of the most common side effects is a decrease in appetite. Patients may find that they are not as hungry as they used to be, which can result in them consuming fewer calories and, consequently, losing weight. Additionally, chemotherapy can cause side effects such as nausea and vomiting, which can make it difficult for patients to keep food down. This further reduces the number of calories they are able to consume. Mouth sores, another common side effect, can make eating painful and unappealing, leading to a reduced intake of food. Moreover, the body's metabolism may increase as it works to repair the damage caused by the chemotherapy drugs. This increased metabolic rate can burn more calories, contributing to weight loss. Finally, the stress and anxiety associated with a cancer diagnosis and treatment can also affect a person's appetite and eating habits, potentially leading to weight loss. In summary, the weight loss during chemotherapy can be attributed to a combination of factors including decreased appetite, side effects that affect eating, increased metabolism, and emotional stress. read more >>

Another common cause is the treatments for cancer. Radiation and chemotherapy often cause a decrease in appetite. They can also lead to side effects such as nausea, vomiting, and mouth sores, which can affect your ability to eat normally, further contributing to weight and muscle loss.read more >>