Actually, the primary reason that I was asking about the diet was to get a sense of fiber intake.
The most common reason for chronic abdominal pain associated with constipation or diarrhea in a young adult is from irritable bowel syndrome, which is due to altered muscular activity of the gut.
While this is very common, there is no test that can prove that this is the cause of symptoms. The usual approach is to perform an evaluation to exclude other possible causes, which would then indicate the diagnosis of irritable bowel syndrome. There are several other conditions that would need to be excluded, such as inflammation of the gut, liver or gallbladder disease, or pancreatic dysfunction.
However, another approach would be to try dietary adjustments. The usual first line intervention
for irritable bowel syndrome is to increase the intake of fiber, ideally to 25-35 grams per day. So, it would also be reasonable to try to increase fiber intake to see if the symptoms resolve. Fiber intake can be via foods or fiber supplements. The foods that have higher fiber content include fresh fruits and vegetables, whole grains, and legumes. If the diet does not contain sufficient fiber, then adding a supplement would be appropriate.
So, it would be appropriate to first try to increase the fiber intake. If this eases the pain and bowel movements, then no further evaluation is necessary.
If I can provide any further information, please let me know.