Wondering,

if we're malabsorptive for only a year, why must we stay on high doses of vitamins for ever?

We malabsorb calories for a year or two because the intestines grow back little hair-like appendages that hold food in contact with the intestines and make sure calories are absorbed.  The parts of the intestines that absorb vitamins from food are cut away and will never grow back, so we always will malabsorb vitamins.

Gotcha!  Thanks. I've been wondering this for a bit!!