Weight Loss Stalled After Gallbladder Removal

I am looking for some feedback regarding the possible causes of weight loss stalling after gallbladder removal.  My husband is 42 years old and had his gallbladder removed in October 2009.  He lost weight immediately from being in the hospital, going from 340 lbs to 280 lbs.  He eats a clean diet, has tried working with nutritionists at Temple University, exercises 6 days a week, cardio, strength training, and is in great shape except for the fact that his weight will not drop.  It is my assumption that he will need to consult with a gastroenterologist and have some sort of bloodwork done, but is there anything specific we should be asking doctors or anything specific we should be looking for in lab results?