I ask...when you eat sushi what are those movements like? Not trying to be gross but before I went vegetarian and also recently tried vegan fruit diets which helped me a ton I used to eat tons of canned fish like tuna, salmon, and I also bought raw smoked salmon which is used as a sushi substitute. Gotta tell ya, the fish, it wasnt as bad as eating grains and starches which really mess me up in terms of making me go a lot/cramps/blood....but still, on mostly protein/meats, the stools were like all watery, smelly, and sometimes I'd have cramps. I honestly thought this was a good diet though because it was less painful than the standard diet I was on (sandwiches, snacks, lots of grains like cereal for breakfast, or bagels for breakfast, etc!). But it really is no way to live.
In general, after 10 years of this crappy disease =), I go by these rules:
The frequency of stools and the wateriness (or blood in my case) can be a sign if the food is digesting well. Smell too but you dont gotta go there I guess. Plus the pains you get while it is passing through kinda tell ya how it is reacting. I'm not sure about you boys, but when I eat something different I just KNOW it was from that....the pains, the way the stool looks, smells, the frequency...its like being a detective really. Unless you are in a constant state of sickness all the time, I've been there too, like it would be pretty much 5-10 watery stools per day no matter what I did. Now I'm down to 1 so it is easy to tell if I eat something that bothered me. Then I never touch it again because I dont like seeing my money go down the toilet...literally. I guess what I'm saying is the Sushi could be better than the other foods you are eating now, or it could be worse...its all relative. Therefore it will either increase or decrease your symptoms if you replaced one of your normal meals with it.
Although I think meat is harmful for crohn's, I would say there are far worse meats you can put in your body than the fish...it is probably one of the better ones except that it is raw, cooked fish is easier to digest...I'm sure you know that. It kinda depends what you are eating with the sushi too though. Rice is starchy and tough to digest with meat and that soy sauce probably irritates the intestines because of the high salt content and soybean. Hmmm...and if you are eating hot sushi. Heres what I truly believe and something my raw vegan book told me. If it is spicy enough to irritate your mouth, it is probably going to do the same to your gut. I've known this before reading the book but loved spicy foods and just kept eating things like tabasco. But seriously, when they serve your sushi with some wasabi and spicy pink radishes maybe think it over b4 ya use that.