Bleeding and diarrhea any ideas? :(?

My father have had this bleeding with bowl movement for sometime now. He had a colonoscopy and endonoscopy. That's the doctors check your insides through mouth and rectum and the results were OK..But the bleeding and diarrhea continues, I feel so bad because he stays in the restrooms for at least 10 minutes each time. He eats normal and works out almost every day. On top of all a very healthy man but with this problem. Does anyone have any ideas of what might this be? Thank you for your help!