I'm almost certain the bi-polar issue was the deciding factor in your friend being rejected. From what the psychiatrist that questioned me said, they are looking to weed out anyone that wouldn't or couldn't accept the responsibilities of the surgery and new lifestyle. Basically, so it wouldn't be a waste of the insurance company's money to put someone on such a drastic course.
I've known a few people who were diagnosed as bi-polar and some are very grounded, provided they take their meds. But for those that do not, expecting them to adhere to their nutritional needs is just too much. If they aren't responsible enough to take their meds, how responsible will they be to eat right, exercise, and follow the rules?