Question: what are the most common gastrointestinal diseases?
Answer: Gastroesophageal Reflux Disease (GERD) Heartburn happens, but if it occurs regularly, you may need to be evaluated for GERD. ... 
Chronic Diarrhea. ... 
Chronic Constipation. ... 
Gastroenteritis. ... 
Ulcers. ... 
Hemorrhoids.