--the ones that are 1000mcg and up--the idea is that one is taking a sufficiently large dose that one can get one's requirements through the 1-2% that will be passively absorbed throught the mucous membranes.

We've had some people who've had gastric surgery who daily took 3000-5000mcg of B12 so that they could count on absorbing 30mcg or each day and help rebuild stores and have enough for some repair processes (the "normal" daily requirement is somewhere around 2-8mcg).

Yes, with gastric bypass surgery you will defintiely be prone to malabsortion of many nutrients--I wouldn't be surprised if you have mineral deficiencies as well (have you been tested fo them?).