All very true, CT! But, I did want to point out that of the typical 15-20 feet of small bowel, only 6-12 inches is used for the pouch, so it really is a quite small percentage. Plus, at least in the U.S., malnutrition due to inadequate intake is rare, since most of us consume far more than is required for health. So, even if it is not as efficient, in most cases having a j-pouch does not mean inadequate nutrition absorbed.
Still, it is another factor added to the pile of various risks, including age.
The main thing is to be aware of the possibility, without assuming you are at high risk.
Jan