Malabsorption Decrease
There are these little tiny things in your small intestine called villi. They are like fingers that grab up calories and absorb them. When they bypass part of the small intestine, suddenly there are fewer villi in there to suck up the calories.
However, your body quickly figures that out and it is afraid it's gonna starve. So your small intestine starts to grow more villi in the part that has not been bypassed. After two or three years, you have about the same number you had before surgery so you absorb about the same amount of calories again.
It's pretty cool if you think about it.
However. We continue to malabsorb vitamins because only certain spots in the small intestine absorb each one of those. That never goes away because some of those spots are bypassed forever. Your intestine cannot grow new ones.
Please note: I AM NOT A DOCTOR. If you want medical advice, talk to your doctor. Whatever I post, there is probably some surgeon or other health care provider somewhere that disagrees with me. If you want to know what your surgeon thinks, then ask him or her. Check out my blog.
If I understand correctly after a couple years the villi ( tiny hairs) in the intestine grow back which contribute to the increase in absorption of calories. I haven't had the surgery yet but have been told that after a couple years you basically absorb calories like a 'normal' person would. Hope this helps a bit.