She may be right, but not all kitties have clinical symptoms......and diarrhea and weight loss are actually clinical symptoms of Hyper-T.....hard to really tell without a thyroid test (T4 or Free T4 by ED). Not all cats have palpable thyroid nodules.
He's not losing weight & has gained since last time at the vet

(I would say close to ideal atm). It's just the increased appetite & poo that I'm primarily concerned about.
Did she have any suggestions for the diet? Is Mim still losing weight?
As usual Hill's "whatever" was mentioned....I showed her the ZiwiPeak but she wasn't familiar with it. I mentioned going to raw, which there was no objection to.