I see you've gotten some really good advice already on the dieting part. Have you also considered mental health? The mind affects the body in a multitude of ways. Not only has this been known in medicine for ages (think of traditional Chinese medicine) but it has been scientifically confirmed with the healing effects placebos can have. A negative issue may be holding them back, they may feel like they are under a lot of pressure... Whatever it is, maybe there's something there as well that will help them get better. My back didn't get any better until I went to a hypnotist who figured out some deep-seated trauma. I couldn't walk properly for a while and mentally I felt like I was stuck. After the session with the hypnotist, my pain was slowly fading away and I'm much better now. Hope your friend gets better!