A friend of my wife (friend since Uni) visited recently. She suffers from irritable bowel syndrome; has for years. Some time ago, her consultant gastroenterologist told her there wasn't anything he could do for her, but knowing she was an intelligent practicing scientist, he wrote a note on a piece of paper and handed it to her and said this might help.
She said he had written "FODMAP". My wife's friend has treated herself and never looked back.