The couple of points here nremtp,
I agree that if you're on a meal break you should not be disturbed until it is over. If you are tucked away in the station eating, then dispatch should not be disturbing your unit, even if the call occurs right outside the hall. In fact there is an on going battle, regarding this issue between the union and management in the large urban service I work for now.
However, It is obvious that if you are out on the street and someone has injured themselves and asks for your help, then there is a duty to act. I understand that it is a busy day and you may be tired and not ate for awhile, but I think it very unlikely that postponing one break puts the patient at great risk, or runs the risk of an EMT's blood sugar getting dangerously low; as you argue. If you were at a Hospital cafeteria and someone started to choke, do you think a doctor would respond with: "no, sorry, can't help now, I'm on a break, I think you can find another doctor upstairs"?