Actually (though one can indeed find estimates that range from as short as 14 hours to a week or more), the official position ( National Center for Biotechnology Information, U.S. National Library of Medicine) is that the lining of the small intestine is replaced on approximately a weekly basis.
http://www.ncbi.nlm.nih.gov/books/bv.fc ... ction.4113
However, that's not exactly true for someone who has MC. With MC, the healing process gets stuck at the first stage (inflammation), and it cannot progress past the second stage (debridement by means of immune system white cells, such as macrophages), so that progression to the third stage (actual replacement with new cells) can only occur on a haphazard basis. The reason why it gets stuck and cannot progress is due to the fact that unlike most trauma (which is typically caused by a single, discrete event), the inflammation/damage continues to be generated on a daily basis, as long as we continue to eat the foods that trigger the production of antibodies.
That's the reason why MC is a chronic (and self-perpetuating) syndrome. I have a hunch that the reason why MC exists as patches of inflammation scattered at random in the gut in the first place is precisely because the healing process is corrupt in those areas, so the cells in those patches are too old, diseased, and long overdue for replacement.
If you are interested in using supplements to help heal the gut, one of the better choices is L-glutamine, which is an amino acid used by body builders to help speed up the repair of smooth muscle damaged during workouts. The intestines are made of smooth muscle. A few members here have had good results with it (while others didn't notice any effect). No one has reported any adverse side effects that I'm aware of.
Beware of some of the supplements recommended at various locations around the internet for healing the gut, because with a compromised digestive system, we can't always tolerate some of those items. As a result, some of them can make symptoms worse, rather than better.
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