Hello. Welcome to HCM. You have not mentioned if he has also been investigated. Loss of a significant weight along with inability to digest food definitely requires routine blood investigations as well as special tests pertaining to GIT ( including endoscopy and biopsy). For a definite opinion you need to mantain a pain diary with precipitating factors and associated symptoms (if any e.g diarrhoea, flushing or sweating etc). So, you must visit a Ge physician who will investigate your brother in a staged fashion and treat according to cause. Take care.