unknown problem help.............

hello! friend of mine who come from srilanka six month before to canada. last 4years he had a problem in is daily food life .he is 45 years old slim body with good health .but the problem was whenever he had food in a few minute or in an hour he will vomit all he had for food not in specific food what ever he had except potatoes . even apple ,bananas and any kind fruites too gives this problem .last four month he regualerly attenting for medical checkup .the doctors also tried some drugs and even info camera to see what is in his stomach but no use they couldn t find any thing about this problem .they keep on tell that he does not have any problems by health wise he was good.but the vomitting continues till now

do u have any remedies for this please help him