Hello I appreciate your concern for your friend This could be IBS (irritable bowel syndrome) or gut infection like worn infestation I would advise him to go for an stool test for ova cyst or protozoa, occult blood or presence of fat He may require a course of antibiotics under supervision of doctor Ask him to have plenty of fluids including ORSand fruit juices during the episodes of diarrhoea Observe good hygiene by washing hands with antiseptic soap or solution before and after taking food or coming out of restroom Hope this helps him Thanks for your question Best wishes