How long you need to wait to exercise depends on how big the meal was. If it’s something small, like around 200 calories, you could probably exercise right after eating. However, if you’re eating a large meal, you may need to wait more like 2-3 hours.The smaller the meal the less it will impact your work out.If you know you’re exercising soon after, don’t stuff yourself.owever, if you’re eating a large meal, you may need to wait more like 2-3 hours. The smaller the meal the less it will impact your work out. If you know you’re exercising soon after, don’t stuff yourself.