Call 1-800-MEDICARE and they will answer all your questions. When I had surgery with Medicare five years ago, they did not require any supervised diet up front. I think they did require a psych eval but they did not require counseling.
Please note: I AM NOT A DOCTOR. If you want medical advice, talk to your doctor. Whatever I post, there is probably some surgeon or other health care provider somewhere that disagrees with me. If you want to know what your surgeon thinks, then ask him or her. Check out my blog.