I can't really give you a full answer. I watched a program a few weeks ago about low carb diets on ITV. The overall impression was that it left people feeling washed out , lethargic and 'headachy'. However, if you’re already on such a diet, then only you will know how you feel.
I don't imagine such symptoms would help during the medical. In particular, I would imagine undergoing the hyperventilation tests would be even worse than normal (not an experience I like to undergo anyway).
There are also blood tests to consider too. I am sure some doctors out there must know! I am interested in hearing their views on this one too.
Bodie