Because of my fairly severe food allergies, my diet is limited (even
more than just being paleo) and I have to cook several things in order
to tolerate them.  Because of this, I sometimes worry about nutrition.
I know that some vitamins break down or otherwise become useless with
heat.  Is this effect total?  In other words, will cooking completely
destroy some vitamins (such that there is _no_ vitamin of that type
remaining) or does it just reduce it in terms of amount?  Is it the time
or the heat that determines if it is destroyed?  And, which vitamins are
susceptible?

Erik