EMom> Yes, I did recommend "Life Without Bread," and I think it is probably the most important book I have read in the past 2-3 years. (Mind you, I was only diagnosed with Crohn's 9 months ago!).
CrazyHarry already expounded upon the carbohydrates, but here's a quick rundown:
Monosaccharides are single (one sugar) carbohydrates; honey is comprised almost entirely of fructose and glucose, for example. These are absorbed "high" in the gut- past the duodenum (where the stomach lets out into the small intestine), but not too far into the small intestine. The body just grabs them out of the gut and stuffs them into the bloodstream.
Disaccharides are two-sugar carbohydrates; table sugar (sucrose) is a combination of one molecule of fructose and one of glucose. From the time you consume it, the body is working on it with enzymes (invertases) that break it up into its component molecules, which are then absorbed as above. Lactose is another disaccharide; many people lack the enzyme to break it down into its component sugars, glucose and galactose. There are other disaccharides, but they are minor in the diet.
Trisaccharides and tetrasaccharides (three- and four-sugar molecule carbohydrates) are found in vegetables and some other foods. The inability of some to do well on asparagus, broccoli, brussels sprouts, cabbage, soybeans, etc. may be due to these complex sugars.
From there, you have oligosaccharides- molecules that are even bigger. I think they are comprised of chains from 5-9 sugar molecules, while polysaccharides are 10 and up. Polysaccharides would consist of big honkin' molecules like inulin, starch, pectin, that sort of thing.
And this model works very nicely to explain why the "gluten free" diet works well for some Crohnies. If you get rid of gluten like a celiac, then you're excluding barley, rye, oats, and wheat- all are seeds that contain huge honkin' quantities of starch. It also explains certain sensitivities to specific vegetables.
In his book, Lutz suspects it's due to the insulin "pulse" from eating carbs; this causes the digestive system to speed up for a bit, which could push carbohydrates that are not sufficiently digested into the large colon. There they feed undesirable organisms, which in turn cause the gut to go haywire.
After a number of weeks or months (I think Gottschall puts it at 3 months) on carbohydrate restriction, there can be a relapse which involves blood, mucus, and pain that may be interpreted by the dieter that it is not working. To the contrary: I suspect this is a die-off of the previous, sugar-fed flora, which is in turn to be replaced by more "normal" flora that can persist on fewer sugars. Interestingly, I have relatives who offer weight-reduction consults through their medical practice; about two weeks into the diet, they report a similar event (minus the blood). The nature of the mucus, etc. was unknown to them and I informed them it's very simple: out with the old flora, in with the new. Cinch.
I would also opine that this mechanism jibes with the theories that MAP plays a role in Crohn's. MAP presumably colonizes the intestine, resulting in portions of the colon that are then susceptible to secondary infection. The ulcers are made worse by organisms- probably fungi- that can attack this raw tissue, resulting in the pain and bleeding, and making the malabsorption worse. The reason I suspect fungi is that they do better on polymeric carbohydrates, while bacteria prefer small sugars. In fact, MAP is a facultative intracellular parasite- it can live off the glucose fed to the body's cells; the polysaccharides should not affect it directly, only indirectly.
This also explains why probiotics tend to help in that recolonizing the gut with more benign flora is imperative once the changeover begins.
Gottschall has it exactly, on-the-nose correct. Lutz takes a less precise approach, but reaches the same conclusions independently.
Meanwhile, your average gastroenterologist will insist that specific dietary measures are unable to control this disease, and if so, certainly not to the degree that it may be interpreted as a "cure." A little tip:
Go to PubMed:
Search for "diet" and "Crohn's." You will go blind and insane trying to make sense of all the studies, some of which say there is an effect, many of which do not.
Then search for "diet," "Crohn's," and "carbohydrate." You will find the field greatly restricted, and much more open to reading with only 132 hits. Now pore over them, looking for studies in which the authors researched Crohn's management through carbohydrate restriction. They are quite old, but they are there; medicine seemed to give up the study after the mid-1980's, but they're there and (best as I could find) they all showed strong positive results.
Net upshot: no, dietary management of the disease does not look like a valid venue- until one looks only at carbohydrate restriction. At that point, the literature is virtually unanimous: it works. You can verify this yourself through the instructions I give above.