Here's an article from Nature that shows mice can become more easily obese if you infect them with some, er, stuff, and that this is transmissible (http://www.nature.com/nature/journal/v444/n7122/abs/nature05...)
So you could be giving yourself stuff that would make it easier for you to become obese, or you could be giving yourself stuff that would make it easier for you to stay not-obese.
And that's just these few bugs. There are a whole range of really quite unpleasant things you could be getting.
Regulations are important. They're not to protect well informed people from making calm rational choices, although they do have that unfortunate effect sometimes. Regulations are to prevent cynical, or stupid, people from offering dangerous untested unproven "treatments" at great cost to desperate and ill people.
It'd be great if there was a safe way to decouple these, allowing people to gamble with their own health if that's what they want to do, but protecting people from evil con-merchants.