I do not know, but the people they certify, and only they are allowed to certify, are working in hospitals and advising patients, and their advice is legally protected by various state governments.

I doubt the dietician giving advice to patients is announcing the conflict of interest.

They are considered "experts" by the media, for one thing. So if you read an article on nutrition and some "expert" or other is quoted, and you act on its advice, then you might be in that fraction.