Snowy had weight issues due to her liver issues - she had raised liver enzymes for 10 months with no meds and just the odd bit of prescription food before it developed into anything more serious - and even then, it was something potentially treatable, just I manage to get cats that refuse all meds (Snowy started hiding from me and stopped purring, which I couldnt have), so fingers crossed Tom's can be controlled for quite a while like hers was, and if you can get him to eat the food, maybe longer. Do remember it is about quality and not quantity though, so if he wont eat the special food, let him have what he likes - and fish doesnt have a lot of taurine in it, so can't be used as a long term diet.