From childhood, I was trained to wait for at least an hour after a meal and that is to avoid stomach discomforts or digestion issues. Now that I have a better understanding of my body, I can very well tell if I'm ready for an exercise after a meal. If it's a low impact and leisurely walk, I don't mind doing it immediately after a meal. In fact, it makes me feel better to walk after a heavy meal. I would wait at least an hour though to do zumba because there are a lot of gyrating motions that's uncomfortable when the stomach is full.