Another factor may be that more people are trying to overpack their carry-on bags to avoid checked-baggage fees, though the airlines strongly dispute this.
You can have a protein shake if that works for you, you can have a protein bar, you can take that with you, have it just before the test, but again, make sure your stomach is not louder than your thoughts.
For instance, the chairs you're sitting in today, the lights in this lecture hall, my microphone, the iPads and the smart phones that you carry around with you -- all are a result of cumulative cultural adaptation.