To be honest in the UK the general advice is that a gluten free diet can do more harm than good unless you medically need it. Most gluten containing foods have a higher sugar content to make up for the lack of taste, and many are high in fibre. By cutting out large amounts of foods, you cut out lots of vitamins etc and yes it is really expensive and a real nightmare when trying to eat out, especially if you're really sensitive to it which coeliacs are.
I would suggest that anyone trying this diet makes sure that their doctors know, and gets frequent blood tests. I have had coeliac for 10 years now and still have yearly reviews with a dietitian which I have to have for the rest of my life, and also have a yearly review about it with my consultant with full panels of bloods for all nutrients as well as blood sugar checks.
I'm not saying that this can't be effective as symptom management for some people, but it has to be done in the correct way. You probably will find you gain weight, because the food is generally higher in calories, for most people your body adapts after a little while.
Also, for someone with coeliac disease it is totally vital to avoid all gluten. If someone with coeliac ate it, then the coeliac would flare and the immune system would become over active, which of course would kick the crohns off, so yes, if someone with coeliac ate gluten it would likely cause an increase in crohns symptoms, but this is probably because of the immune systems response rather than the gluten on its own. In the case of someone with coeliac, it takes about 6-12 months for it to work completely because that's how long it takes to repair the damaged villi, but most people will notice they start to feel better much sooner than that. I don't know if the time span actually applies in the case of people going gluten free for other reasons.
