Pigeon, I'm not a big fan of not being straight with a doctor, but ...
The doctor needs to know your symptoms (frequent urination/frequent thirst) and if s/he asks 'has anything in your diet changed recently?' you could legitimately say that you are eliminating sugar and refined processed foods. That's often an acceptable way to present low carbing to a medical professional who might cringe if you actually said you were following Atkins, but who will be all for getting rid of sugar and processed foods. I wouldn't even call them 'carbs' if you think your practicioner is phobic about it...

Don't lie...but in this case, don't give them more information than they'll use constructively.

That said, if s/he gives you the test, and you DO come up with symptoms of a disorder, be very specific about what you're eating, when symptoms started, etc.

Trust me, cancer docs don't want to hear you're on some crazy low carb diet either (unless they're pretty enlightened...) But they do love to know that I avoid sugar and refined and processed foods. And when I started to respond to treatment, the nutritionist and nurse practicioner became *very* interested in what I was eating, and started to draw their own conclusions and do their own research about the value of low carbing for cancer patients. Sometimes, you have to let them get to the well on their own two feet.

Gaelen