Why do I get gassy if I don't eat?

Swallowing air. There are many causes of flatulence, usually these are related to types of food or GI disorders. You may be swallowing air due to repeated swallowing motion, when hungry. See this site for more info. http://digestive.niddk.nih.gov/ddiseases/pubs/gas/
Digestion. gas forms from the digestive enzymes from saliva, stomach, liver, gallbladder and pancreas. I suggest an examination and abdominal ultrasound to rule out gallbladder disease.