what benefits do students get from being fit and healthy?

Answer 1

http://en.wikipedia.org/wiki/Mens_sana_in_corpore_sano

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http://www.livescience.com/7990-sound-body-equals-sound-mind-study-finds.html

... and many others.

This is a very old concept, somewhat based on Aristotle's and others' idea -- "moderation in all things."
http://www.philosophypages.com/hy/2s.htm

Read widely. Take good notes. Let us know what you decide to write.