It is safe. It can cause upset stomach and nausea. If it does don’t do it.
Actually don’t do it because it is pointless. What fat soluble means is that if there is no fat in your digestive system (a side effect of fasting) there will be no way for you body to absorb the vitamin that has no fat to be soluble in.
But you can still get the upset tummy. All the possible side effects and none of the benefits.