During exams a poor diet can led to fatigue and also increases stress levels. Students need to remember that skipping meals for studying or eating at odd hours can have adverse effect on their performance. You should have all your 3 proper meals in a day. While studying there is definitely energy loss, so it is advisable to munch on healthy snacks like dry fruits, fruits and roasted nuts. Keep yourself hydrated with atleast 8 glasses of water and some fruit juice. Do not over eat and avoid junk food. You don’t want to feel sleepy or lethargic during exams.
I second that a good diet can be helpful to reduce stress level. Also dark chocolate and almonds are good to reduce stress level. You can also try Rum Balls.