The problem with measuring the fluid left after marinating is that fluid is exchanged between the meat and the marinade. If the marinade is far different in calorie density than what is lost by the meat, your count will be off.
Is the accuracy really that important? Most of the time probably not.
What I do, as much for practicality as calorie accuracy (it saves money and waste) is to marinate foods in a plastic container or ziploc bag and use much less marinade, and marinate a little longer. The ziploc bag is ideal, because you can squish the meat around in the marinade, and turn the bag over several times during marinating to insure that the marinade is getting into the meat. So less marinade goes far further. By doing this, there's little or no marinade leftover, so it all can be counted and divided by the number of servings.
Last edited by kaplods; 04-02-2010 at 03:50 PM.