This one is not always straightforward. My personal advice is that if it seems your child is annoyed by this question, then strike a deal. If your child is seriously bothered by this, try again working a deal. Maybe you can come in at the end of the appointment to ask any questions you might have. Or maybe your child will let you phone the doctor the next day.
Independence is so vital to teenagers - try to compromise.
In the present day of carb counting, there is nothing that you cannot eat at least occasionally. This comment usually comes more from uneducated relatives, co-workers and friends. This is what my father said 15 years ago and I still wish he had never said it. We had to stop every 15 minutes because I really, really had to go to the bathroom. It took us about twelve hours to finally get there.