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How to gradually transition cat food for a diet trial or IBD symptoms?

Updated on September 23rd, 2025

Pet's info: Cat | Mixed Breed | Female | spayed | 13 years old | 6 lbs

My cat (13yr) lost lots of weight (now 6#), eats tons, has loose stool, and vomits occasionally but not often. A vet found no masses, and blood and urine panels came back clean. Now I suspect IBD and want to try a food trial. The instructions on this peteducation.com website for a 12wk trial don't mention easing in or out of a trial, but I thought changing food abruptly causes GI problems, which is exactly what I'm seeking to eliminate with the trial. Should food trials be eased in and out of?

2 Answers

Most Helpful Answer

Lauren Kennedy, DVM

Answered By Lauren Kennedy, DVM

Veterinarian

Published on January 30th, 2018

Yes, it is always good to gradually change over to a new diet rather than doing it abruptly. I usually recommend a period of about 5-7 days to switch food.

Start with 25% new food, 75% old food for 2-3 days, then increase the ration to 50:50 for a few days, then further increase it to 75% new,
25% old for a few days, then 100% new food.

I hope the diet change does the trick for Z. Best of luck. Let us know if you have any additional questions!
Vote Icon1Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Sarah Box, BVSc

    Veterinarian

    Poor Z-it sounds like she has a lot going on!! Did your vet check her thyroid hormone level? Hyperthyroidism is common in older cats and can definitely cause some of the signs you have been seeing.
    Regarding your question for transitioning to a new diet: yes-ideally you would spend 7-10 days transitioning to a new food. Start by mixing just a small amount of the new food in with the old food you offer her. By about day 5 you would expect to be at a 50:50 mix and by day 10 completely transitioned to the new diet.
    Be sure and discuss your concerns for IBD with your Vet before starting a diet trial-your Vet may have some additional recommendations and may even offer some diet ideas for you to try that may be most suitable.

    Vote Icon

    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

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How do I gradually switch my cat's food to a new one without problems?
It's recommended to do it gradually over a period of 1-2 weeks, you need to mix the new and old food, start with a small amount of the new food the first few days and gradually increase the amount of the new food and decrease the amount of the old food.
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Cat has diarrhea after new food. How long until she adjusts?
Her stool in the 2nd and 3rd pictures still look a little soft, so I would give it another couple of days on the 25%/75% mixture before going to 50/50. If when you do make that switch to 50/50 and she starts having diarrhea again, then I would say that this food isn't agreeing with her and keep her on her old food instead. I say that because if you've tried the 50/50 mixture, got diarrhea, went back a step for a bit before returning to 50/50 and still get the same result, then it's not a food that agrees with Kitty. Best of luck, I hope this helps!
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My cat has sensitive GI. Is a 10-day food transition long enough?
Great question! Yes, the transition you described for Kitty is just fine. If you do notice any GI upset, go back to her old food and take five days between each transition to the new food. Best of luck!
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How do I safely switch my kitten's wet food without upset stomach?
You can switch their food but you want to slowly transition them to the new food. This means you want to start with mixing only a small amount of the new food in with the old food for a few days then over a 10 day period, increase the amount of new food while decreasing the amount of old food until you are just feeding the new food around day 10. By slowly transitioning them to a new food, it decreases the risk of causes an upset stomach. I hope this helps!
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Can I transition my dog's food 50/50 for seven days safely?
Rather than using a 50/50 mixture for a diet transition, I would instead ideally recommend starting 75/25 old/new food for 2 days, 50/50 for another 2-3 days, then 25/75 old/new food for another 2 days. Chloe is more likely to experience gastrointestinal upset without the more gradual transition. That said, it is possible that she could be perfectly fine with a more consistent 50/50 transition over 7 days. If she does not normally have a sensitive GI tract, you can try a 50/50 mix for 7 days, but if she does develop signs of a GI upset (vomiting, diarrhea, loss of appetite), a more gradual transition will be necessary. I hope this helps clear up any confusion!
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Pet food transition: How much new food and how long should I take?
If you are wanting to switch Kiko to a new food the best way to do it is to transition him slowly from the old food to the new food over about a period of one week. I usually recommend doing about 25% of new food to 75% of old food for 2 to 3 days then increasing that to 50-50, then increasing it 2 to 3 days later 75% new to 25% old and so on. By the end of 7-10 days you should be able to successfully start them on the new food without any problems. Signs to watch out for that can indicate a food intolerance to the new food include vomiting and diarrhea/soft stools. Good luck.
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Is it safe to switch my dog's IBD diet from Royal Canin to Hill's z/d?
Theoretically Trixie could do any of the hydrolyzed diets. Royal Canin carries a hydrolyzed protein diet very similar to the Hill’s diet. Purina also carries a formula as well called HA. Most likely Trixie would do fine on any of these. Make sure any diet transition is slow over the course of 5 to 7 days. I hope this is helpful and please feel free to post any additional questions!
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