Jones has IBD(possible lymphoma) and had severe pancreatitis, that if something made anything flare up I was done with that food. He lost a tremendous about of weight and with the diabetes from the steroid given (pred), I needed him to eat! And I did the dance - he would eat something for two days and then stop eating eat it. I had food everywhere.
Have you ever considered allergy testing? It was suggested by a member here to get Jones tested (which the clinic one can be expensive) but actually suggested this one.
ImmuneIQ. This is linked to groupon where you can order it. Best money I spent so far I think. You will see a line in my signature - Allergy Report if you want to see a sample of the report you will receive. It was quick and easy. It at least allowed me to know the red zone items - what to definitely avoid! Which oddly enough I was giving Tuna as an enticement to eat - that was the wrong thing to do! I recently went through all the food I was feeding him and ones I wanted to try to see how many of them had red zone (allergic to) items in it or a lot of the yellow zone(don't hurt but don't help either) items. It was an eye opening experience. Since I have done that and selected the best canned food I can, he shifts less frequently and it more of a - I am done with salmon, can I get some lamb please type of thing.