Wow.  This is interesting to learn about the effect of
heat on lactose.  I already knew that mozzarella,
among cheeses, is the one containing about the least
amount of lactose (according to info sent me by the
Lactaid people when I called their 800 number).  And I
knew that the concentration of lactose in cheese, milk,
or ice cream increases when the fat content is reduced.
Thus, I thought that I could (almost completely) tolerate
the pizza from inexpensive pizza "joints" because they
probably use low cost (=low quality=fatty) mozzarella.
(Actually, I've wondered to myself whether some places
are really using melted rubber on the pizza rather than
cheese!)  Now I know that it may also be a result of the
intense heat.  The only pizza that I eat at home are the
Stouffer's French Bread Pizza's which are not
extremely cheesy, and the whey in the French bread, if
there is any, doesn't bother me much if I take a few
regular strength Lactaid pills.  That fact that I can still
eat pizza is one of the only things that has made my LI
bearable.