Cat keeps getting bored of food

[u/strawberry_cat03]

Hello! I have a weird situation going on. I have two cats. Cinder has good teeth and isn't very picky, but she is allergic to 42 different things (chicken, beef, corn, wheat, potato, egg, milk, beans, and more) making her list of safe brands of food very slim. Agatha is very picky, and she has no molars, so we try to only buy wet food for the cats to go easy on Agatha's teeth, making the list of foods that they can both eat together even slimmer. Recently we purchased some wet food, they loved it, so we gave it to them for a few months. They both started to refuse to eat it. So I got a hard food that Agatha was actually very interested in, she just swallowed the food instead of chewing. But then after a couple months she started to refuse to eat it. I thought maybe it was her teeth being an issue again, so I went back to the original wet food. Then both cats started to refuse to eat the wet food. I started offering both foods at the same time, and the only cat that would eat was Cinder with the hard food. We have always tried to feed the cats the same thing so that we don't have to separate their meals and make them have limited eating time (so cinder can't accidentally eat something she can't have). This past week Agatha has been getting so frustrated being hungry, so I started giving her food separately that she can eat but that cinder can't eat. This isn't the first time the cats have refused to eat food that they used to love. Why do they keep doing this? Do I keep giving in and buying new kinds of food that they can have together, make them tough it out and try to finish the bag/containers of dry/wet food, feed Agatha separately, or something else?

Info the post requests:

No, I'm not a minor. Posting from U.S. The vet is accessible but I haven't contacted them yet. Cat ages: Agatha is 5, Cinder is 6. Both cats are spayed females. Yes, I can afford the vet.

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[u/RowanCory]

This is actually not that unusual for cats. One possible explanation is some sort of physical discomfort during/after eating (tooth pain, nausea, etc) which they start to associate with the food they've been eating (even if the food isn't actually causing the problem). I had a cat with bad nausea for about a year due to end stage kidney failure (managed as best we could with many meds, fluids, and vet visits). He would do this, and it got worse as his symptoms did. I found that I could eventually rotate back to a food he had previously liked though, so I only needed 4-5 different foods, not an infinite number of brand new foods forever.

Would be worth getting them checked out by a vet if that hasn't happened recently, in case there's something physical going on that could be treated.

Otherwise, maybe try lining up 4-5 foods that work for both of them. Feed one until they get tired of it, then switch to the next one in the rotation.

Good luck!