I think it's 50/50.
Even though you could have an illness diagnosed with labs to back it up (that something is truely in your body causing this), you still have to want to fight it. You have to have the mind set to get better. You have to be willing to eat right. Be willing to cut out all the bad things in life. Willing to deal with the up's and down's of the long road ahead of you and your recovery.
So, I say 50% in your body, and 50% in your mind.