Why do weight and muscle loss happen?

One cause is the cancer itself. For example, in an effort to fight the cancer, the body produces substances called cytokines. These substances can lead to weight loss, muscle loss, and a decrease in appetite. 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. Fatigue is also a factor, since the decreases in exercise and other physical activities that happen when you’re not feeling well can also contribute to muscle loss.