Bloating on its own can be caused by several factors, including menstruation, ovulation or even high salt intake--basically anything that causes liquid to pool in the abdominal area. However, when it is coupled with loss of appetite, the cause is almost always related to a problem somewhere in the digestive system. In fact, a loss of appetite is often the body's own way of treating digestive distress by turning off the appetite to allow the digestive tract time to rest.
Bloating and loss of appetite can be caused by infections of the gall bladder, appendix or intestines. With these conditions the bloating and loss of appetite present with severe pain and sometimes fever. They require immediate medical attention.
Gastroenteritis--a stomach virus--is a common cause of appetite loss and bloating. Viruses also include noroviruses or rotoviruses. These viruses spread quickly by eating infected food or using infected objects (such as a phone). Treatment for digestive viruses according to the Mayo Clinic, is usually rest and fluids and light meals as tolerated, but there is no medicine available to treat them. They usually take a couple of days to run their course and have no lasting effects.
Although rare, there are some cancers that cause both bloating and a loss of appetite. They include stomach cancer, pancreatic cancer, intestinal cancer and ovarian cancer. Symptoms for these diseases may be constant or intermittent, and are sometimes accompanied by pain. If there is no other reason for your bloating and loss of appetite, seek testing for one of these cancers.
Gastritis is the inflammation of the stomach lining, according to the Mayo Clinic. It can be a chronic condition characterized by a long-term dull pain and feeling of fullness or have acute onset. Untreated it can lead to stomach ulcers. It is usually treated with acid blockers, antacids or--in the case of a bacterial infection--medication to treat the H. Pylori bacteria.
Chronic constipation doesn't usually cause a loss of appetite, but an acute bout of constipation can cause loss of appetite and bloating because the colon is too full to allow any additional food to pass through. Treatment is usually with laxatives and/or fiber, but occasionally additional intervention is needed if the fecal material is impacted.
A simple reason for bloating and loss of appetite is overeating. This causes the stomach to distend and it takes several hours for the food to pass through the digestive system, restoring your appetite and relieving the bloat.