In my opinion/experience, there are a few ways food affects GI trouble:
1. high fiber/irritating food - Raw fruits and veggies, nuts, seeds, maybe alcohol and very spicy-hot things will irritate inflamed intestines and cause some trouble. The cause and effect is pretty obvious.
2. Starch/carbs - this one is a little controversial. According to those who follow the specific carbohydrate diet (and similar), high carb diet (starch, disaccharides, etc) can change the population of bacteria in your gut, increasing the numbers of bacteria/microbes that your immune system is reacting to. The cause and effect relationship would be harder to recognize since it could takes weeks of eating too much starch to shift the population of gut bacteria to something that would cause trouble. Similarly, it could take a long time on a low-carb diet before you see any benefit.
3. Immune-reactive food - long term GI trouble may disrupt the complicated relationship between your immune system and intestinal contents. Some people get tested (ie - Entero labs) for IgA antibodies against things like gluten (wheat), casein (dairy) and certain proteins in soy, eggs, oats, chicken....lots of other foods. It probably is not the cause of Crohn's, but if your body reacts to these things, then you won't feel good eating them.
4. FODMAPs - A hyper-sensitive gut will not like anything that tends to drawn in fluid or produce gas (that stretching/inflating of the intestines will be painful or trigger intestinal trouble). This seems to be especially relevant for IBS. A low FODMAPs diet avoids apples, onions and a long specific list of fruits and vegetables.
....so, I guess what I'm trying to say is that if you decide to follow the Specific Carbohydrate diet (like #2 above), you have to also keep in mind #3 above. SCD allows dairy products, but if you're having a reaction to casein you may not notice the benefit of the SCD. You'll have to consider all of that.