Decompression methods vary from person to person. Your brother is in his twenties, so there should be a set of soothing methods. Diet recipes don't need to be adjusted for staying up late, just follow a healthy diet on weekdays.
I think it is very important to adjust the time and food intake of three meals a day. People say, "Eat well in the morning, eat well at noon and eat less at night." This is not suitable for people who stay up late at all.
For those who stay up late, when they have just finished studying in the morning and are sleepy, they should eat less and pad something to avoid being hungry and uncomfortable when sleeping. The afternoon is just the time to get up, and we should also enter the preparation period of staying up late, eat more and be full, and make material preparations for the big projects behind; The whole night is a period of high-speed brain operation, and physical strength is also consumed. In this process, we should prepare some snacks, fruits, milk and other foods to replenish our physical strength and spirit at any time. You can also soak some scented tea or American ginseng tea to refresh your mind.
There are still more than two months before the exam. Giving him more care, encouragement and support will greatly boost his morale!
I hope the answer is useful to you, and I wish my brother success in the postgraduate entrance examination!