UnXmas.. The answer is body mass.. I went from 245 lbs to less than 170 in 3 months.
I agree that dieticians/nutritionists can screw up.. or give bad advice.. or poor advice. I think that Crohns is problematic for medical professionals of all ilks. Giving anyone a custom tailored diet/nutritional plan isn't something I'd consider feasible, practical, even logical. Why? Well, what exact damage has the disease done to a patients GI tract? My guess is that even with the best diagnostic imaging, scopes, etc., what one person can tolerate, absorb, benefit from.. is going to be vastly different than the next patient. I think that is why keeping a food diary is so vital. A nutritionist may tell you that this or that is good food... but, if your food diary indicates it isn't a good idea for 'you', then avoid it. I discovered I was extremely intolerant of lactose back then, and I avoided it in dairy products. But I was still having issues. Nutritionist taught me how to 'read' food labels... and I discovered lactose was in lots of stuff.. like margarine.. or vitamins.. I never would have guessed. And recently, with the diabetes... before seeing a diabetic nutrition counselor, I had eliminate sugars.. But she taught me about carbohydrates. At my 3 month labs, thanks to controlling diet, my sugar levels are about 6.3, near normal.
If you know all there is to know about diet, nutrition, etc., then don't waste your time. But, if you don't, seeing someone who specializes in that field, especially if applicable to your specific disease.. it seems like there is a lot of potential benefit to be had for you.