You should tell the truth. But you don't have to tell every detail in every conversation.

If you say "I'm a personal trainer" or "I'm a dietician" or whatever description most accurately applies to you, and stop there, you've given a complete answer to the question. Anyone who wants to take offense --- well, frankly, they'll find a reason to take offense no matter what you say.

A short, accurate statement should suffice.

Disclaimer: I've never been in your position, so I have no right to give advice on this subject.