What are some gastrointestinal tract disorders that include abdomen pain and loss of appetite?

Abdominal pain and loss of appetite are very unspecific symptoms. They can stem from pretty much any disorder in the gastroinstestinal tract, and even from disorders elsewhere in the body. A common gastrointestinal infection by rota- or noroviruses ("stomach flu") for example can feel bad but might cure itself after a few days. Irritable bowel syndrome can cause recurring pains and could be caused by a variety of issues.

Occassional abdominal pain or loss of appetite can happen just because you ate something that didn't agree with you. If you have prolonged pains or seem to have lost your appetite completely, you should urgently see a doctor to determine where the problem lies.