What is a common cause for moderate stool and gas build up in the ascending colon that is causing severe constipation?

Some possibilities..: In an otherwise normal, healthy, young adult, causes of gas, bloating, and stool changes may be due to dietary items. Very common is lactose intolerance, which one can figure out if the symptoms go away after avoiding ALL lactose for 3-4 weeks, and symptoms return upon drinking dairy. Eating excess fiber or eating sugar alcohols (diabetic sweeteners) cause similar symptoms. There are other causes.