Please see this link for information that Princeton has provided on the effect of its grading policy.
Princeton University - Dean of the College - FAQ
It’s pretty clear that the vast majority of grades given out are A’s and B’s. As to the question “What do Princeton students do to both maintain their grades AND health/physical shape/sanity,” the answer is going to vary from student to student. This may be unusual, but my child actually eats much healthier and exercises much more regularly at Princeton than when in high school. I think a healthy life style is among the ways my child remains sane.
Also, as alummother says for her child, there are several periods during each semester when my child’s consumption of energy drinks each night far exceeds the number of hours slept. Between study and ECs, in which my child is heavily involved, there is not a lot of down time, but my child prefers to be busy.