Senior diet for hyperthyroid cat, now stable

A 12-year-old Tonkinese with a hyperthyroid history — even a stable one — means you're right to think carefully about diet, because what you feed now can really affect how well that stability holds and how well the kidneys cope long-term. Senior cats generally do better with higher protein, reduced phosphorus, and plenty of wet food for hydration. But with a thyroid history in the picture, the details matter more than usual. How long has the hyperthyroidism been stable, is she on medication or managed another way, and what are you currently feeding her?

That's a really good position to be in — stable thyroid on methimazole, kidneys clear so far. Here's the thing to know: treating hyperthyroidism can actually unmask early kidney disease, because high thyroid hormones were artificially boosting kidney filtration. So the fact her kidneys look fine a year in is genuinely reassuring. That said, keeping phosphorus moderate and hydration high is still the smartest move at this stage, which is exactly why shifting more toward wet food is the right call. You mentioned she's fussy — does she have any preference for textures, like pâté versus chunks in gravy?

That's helpful — pâté-style is a good base to work from even with a fussy cat, and rotating proteins can help with the boredom factor. Given her age, the thyroid history, and the need to keep phosphorus in check without restricting protein too aggressively, I'd recommend Royal Canin Renal wet food in the loaf texture. I know 'renal' sounds alarming when the vet hasn't flagged kidney disease yet, but this is actually ideal preventative nutrition for her situation — it's specifically formulated to reduce kidney workload with controlled phosphorus, while still delivering enough high-quality protein. It's highly palatable for many fussy cats too. You can find it on Amazon UK in multipack pouches, which keeps it cost-effective. Keep her on the methimazole and continue those regular thyroid and kidney checks — diet and medication working together is the best protection at this stage.

Completely understandable concern, and it's worth knowing that Royal Canin Renal is available over the counter in the UK — you don't need a prescription to buy it. Prescription renal diets are a separate category for cats with diagnosed, active kidney disease where more aggressive phosphorus restriction is needed. What you'd be choosing is a supportive diet that's appropriate and sensible for a senior cat with her background, not a medical intervention. That said, it's always worth mentioning the diet change at her next vet check — your vet will almost certainly be positive about the direction.

You don't have to go cold turkey on dry food, but tilting the balance strongly toward wet is the right move — aim for wet as the main event, maybe 80-90% of her diet, with dry as a small top-up if she enjoys it. Hydration is one of the biggest factors in kidney health for senior cats, and wet food does that work passively without relying on her to drink enough water. If she does stay on some dry food, look for a low-phosphorus senior variety rather than a standard adult formula. But honestly, if the Royal Canin Renal wet lands well with her, she may naturally lose interest in the dry anyway.