I don't have Chron's (Ulcerative Colitis here), but I agree with other comments on this thread on the reality of diet and IBD/IBS. I do think diet can exacerbate or soothe some symptoms, but it is not the overall reason for progression or aggravation. When I am having a flare of UC, I do typically revert to the B.R.A.T. diet for the entire time I'm flaring to be safe, but eating gummy bears and things like that should not be the reason he is still suffering on such a strong medicine. I am not on immuno-suppressants like Humira, but know they come with an increased risk of infection - perhaps he has contracted a bacterial infection from doctor's visits, etc., and that is really what the problem is? Remember the immune system isn't what it's supposed to be on those medicines, so he will probably get sick easier than he used to.
I do also believe his symptoms need to be reported back to his doctor and that further testing and samples should be done. A week is plenty of time for most medicines to have at least kicked in and if absolutely no relief has come along by now then there is something else underlying that needs to be checked.
I'm not saying he needs to go to the emergency room, but definitely follow up with his doc and let him know he's not doing any better! Good luck!
P.S. - Oh, and lactose! Like scifigal2k said! Keep him off ALL dairy! Couldn't hurt.