if you ate during intense exercise your body would simply throw it up.. this is the time the body is under tremendous stress and overload. throwing food or protein powder at it during this time will only stress it more and will actually impede your workout significantly. the only thing that is okay DURING exercise is water and electrolytes and i want to be clear you want to sip, not gulp. runners who drink a lot during their runs do experience a slowdown, so most will swish fluids and spit
also don't eat within an hour or two of your workout either for the same reason. unless your workouts are very weak