I know exercising, and when given the proper nutrition - the bones become more dense too. When your muscles are worked - when given the proper stimulation - they will grow.
Same thing with your mind, and learning: Given the proper stimulation, it will heal.
Without those substances necessary for building, you will only live off your own body. You body will steal nutrients from other sources that have it in abundance, and put it where it's most needed. Obviously, this is only if you haven't been taking anything to replace what's lost during the day.