Mushroom's are pretty Me Friendly because my particular brand of Crohn's is not usually obstruction. The only reason anyone ever tells you to avoid mushrooms is because of the high fiber content, but in that regard they are friendlier than many leafy vegetables, and so, grief-stricken by the absence of kale and Brussels sprouts from my diet, I console myself with mushroomy magic.
One of the least known traits of mushrooms is that they are rich in vitamin D, whose important role in preventing/ameliorating Crohn's has been discussed on many venues of late (specifically in reference to a Canadian study just released in J Biol Chem, and a French theory published in Medical Hypotheses).
Shitake extract has been patented as protective in inflammatory bowel diseases (both Colitis and Crohn's). It has been known that mushroom extracts generally have an immunomodulatory effect, activating cytokines (including TNF-alpha). The Shuvy group demonstrated in 2008 that the Shitake extract Lentinan increased concentrations of TNF-alpha in the spleen and liver of mouse models of Colitis. They also showed that this increase was correlated with improvement in Colitis severity (as measured by mini-resections and immunohistochemistry, which is an impressive measure that many studies of digestion in IBDs lack, but I digress...). Like many other treatment therapies for IBDs, Lentinan was previously shown to be effective against tumors (Kidd 2000). As a member of the Crohn's club but not the Colitis coterie, I would have preferred that Shuvy et al also looked at TNF-alpha levels in the intestine; alas, some other time and place.
But, of course, medicating by patented herbal supplement is quite different than through diet. You will not see the grandiose effects of Shitake extract from just eating mushrooms a few times a week. In the long term, however, exposing your intestines to the B-glucan in Shitake mushrooms may prove equally beneficial. This is why we need longitudinal nutritional studies that augment experiments on petri dish cell colonies.
And with that, we ascend from the mouse studies of Colitis, and move up to the clinical studies specifically on Crohn's in humans.
A large study by Petermann et al suggested that more people in NZ report intolerance to mushrooms (and corn) than beneficial effects. Among those people reporting adverse effects from mushrooms, there was a higher frequency of the gene OCTN1 than in the general OR mushroom-friendly Crohn's public, suggesting that the gene had more to do with the mushroom adversity than did the Crohn's.
The occurrence of the OCTN1 gene variant among the Crohn's population is not consistent between European and NZ studies, and has yet to be performed in the United States. I do not find this surprising as even between individual Crohnies of the same community there are variations in food tolerance: the same diet than improves one person's condition may exacerbate it in another (Jowett et al 2004; Riordan et al 1993).
However, the subjects in the Petermann et al study who had the variant OCTN1 gene showed a bias toward intolerance of mushrooms. It is the first I have read of a gene-diet interaction specific to Crohn's disease, and it is awesome. Additionally, it does not exclude mushrooms as a healthy food in a Crohn's diet -- that is to say, if said Crohnie seems to be able to tolerate them. Rather, it explains why some Cronhies can handle mushrooms (ostensibly without OCTN1 vatiation) and some cannot (ostensibly with OCTN1 variation).
The only other Crohn's-mushroom study I can dig up is a 1989 report that, unless chewed with great care, mushrooms maintain their shape and size and can cause obstruction in Crohn's patients (Tschundi and Schmid).
As a final thought, most diet books say that Shitake mushrooms are the easiest to digest, but that fiber can be a harmful factor (homage to obstructions, again) and to eat cooked with other vegetables or gains to reduce an adverse reaction (Raven, The Definitive Guide to Foods & Herbs for Crohn's, Colitis and IBD).
Yay! I always cook my veggies- never, never raw, but I can't imagine anyone eating a raw shroom. I like them because they are a good sub for red meat which sometimes messes with me. Mushrooms and gravy and mushrooms and pizza are just beautiful. Now I have an excuse to eat more!
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