How do we know Hitler had Irritable Bowel Syndrome?

"Hitler's health has long been the subject of debate. He has variously been said to have suffered from irritable bowel syndrome, skin lesions, irregular heartbeat, Parkinson's disease, syphilis, and a strongly suggested addiction to methamphetamine."

Did he complain of constipation and bloating or what?

: http://alcoholdrugstreatment.info/how-do-we-know-hitler-had-irritable-bowel-syndrome