I tried this on pork loins and it was so good. My whole family loved it.
3/4 cup balsamic vinegar
1/4 cup olive oil
2 tsp. brown sugar
1/4 cup sweet onion, chopped
I marinaded 7 pork loins, fat removed, for about 3 hours. I then grilled the pork.
I have also tried this on chicken and it was also very good. I'm sure it would be great on beef as well.
Since their is only 2 tsp brown sugar over the whole recipe, I'm sure it wouldn't count especially since it was for 7 servings.