How to Switch Your Pet’s Food

Golden retriever smiling with two grey and white kittens smelling plates of food

So, you’ve decided that it’s time to change your pet’s diet – perhaps there is a need for your pet to begin a prescription diet, or maybe you just want to switch to a different brand. While there are many reasons for a diet change, there are a few basic rules to make the process as easy and painless as possible.

First, we will go over some rules and tricks that apply to both cats and dogs, and then discuss differences between the two species when it comes to diet transitions. You need to realize that changing your pet’s diet will take time – possibly a week or more! Plan ahead for diet changes (unless it’s an emergency, of course), and don’t wait until you are out of your old food to switch to a new brand. 

Special Note if Your Cat or Dog is Switching to a Prescription Diet

If you are switching to a prescription veterinary diet – perhaps your pet has a sensitive gastrointestinal tract, has bladder stones, or is being tested or treated for food allergies – you need to know that getting your prescription approved, filled, and shipped or picked up may take several days. Again, it’s important to plan ahead when implementing any dietary changes. 

How to Start Your Pet on a New Diet

Once you have both your old and new diets on hand, you can begin the transition process. Use a percentage rule when preparing your pet’s meals during the transition. Begin by making up your pet’s portion with 75% of the old food and 25% of the new food. Keep using this ratio for several days and monitor closely to see whether your pet is eating both the old and new brands. After 3 to 5 days, increase your ratio to 50% old food and 50% new food. After 3 to 5 more days, increase to 25% old food and 75% new food. Eventually, you will work your way up to using only the new diet. 

Common Side Effects After Transitioning Your Pet to a New Food

The most common side effects that scare many owners away from finishing the transition process are GI disturbances, such as diarrhea, vomiting, nausea, or increased flatulence. Just as humans may experience some of the same symptoms when traveling to a new part of the world, eating unfamiliar foods, or drinking unfamiliar water, your pet’s GI system is acclimated to the type of food that they are used to. Any change can be quite drastic for them. They do not experience, for the most part, the variety of food that humans do on a regular basis, so even small changes can cause upset.

If your pet is experiencing mild signs, such as diarrhea, flatulence, a “gurgley” stomach, or has a decreased appetite during the transition, I would encourage you to continue the process. Stay at the ratio of old to new food until your pet’s symptoms subside, and only then go up to the next step. 

To support a pet who is experiencing mild GI discomfort as described above, use a probiotic supplement. Probiotics come in many forms, but they are available over the counter (no prescription required). They add lots of healthy gut bacteria to help support your pet’s GI system. While we do not promote or work with any specific brand of probiotic, there are several brands that are widely accepted as reputable and proven to work, including Fortiflora (a powder), Proviable-DC (a capsule), and Pro-Pectalin (available as both a tablet and a paste). Regardless of the format or brand that you choose, keep in mind that probiotics are considered supplements, meaning they are not regulated in any way by the government. Purchase a probiotic that is specific to felines or canines, as they have different bacterial needs than humans, and purchase from a reputable company that can provide evidence to show that their product works as advertised. When used appropriately, probiotics can be an excellent and simple way to support your pet’s GI tract during the dietary transition process. 

Severe Side Effects of Transitioning Your Pet’s Food

Is your pet experiencing more severe side effects? If your pet is vomiting repeatedly, begins to refuse food altogether, or if its diarrhea does not improve or worsens over the course of several days, we would recommend backing off your diet transition: either step back to a lesser percentage of new vs. old food or discontinue the new food altogether for the time being. You can always begin the diet transition again, more slowly, after starting a probiotic for GI support. If the symptoms do not improve, seek the assistance of your veterinarian to help you get your pet back to normal and to help advise you through the transition. 

Special Considerations By Species

Finally, let’s discuss some of the different rules that cat owners and dog owners need to consider for their pets. Although similar in many ways, cats and dogs do react differently when experimenting with new foods, and thus need different approaches from their humans to help them work through the process.

Changing Your Dog’s Diet

Many dogs have a preference for their old, familiar food. If they don’t initially enjoy the new food it doesn’t mean that they never will – dogs just require a little bit more patience and, if necessary, some tough love from their owners. Letting a dog get hungry enough to eat new food is OK (in normal circumstances with a healthy pet!). Many times, owners will feel bad for their dog and relent by feeding treats, human food, or the old food to ensure they are not too hungry. Once your dog learns that he only needs to wait you out, he will be less inclined to eat the new food. 

Changing Your Cat’s Diet

We will give cat owners almost the exact opposite guidance, in a twist that exposes a key difference between these two species. Cats must not be starved into liking their new diet; because of this, their transition may take longer or require more effort from the owner. If cats do not eat for a while (this varies from cat to cat, but generally for only a few days), they can suffer serious and even fatal consequences. Ensuring that your cat is eating something during the transition is extremely important. Try to make your transition slow and encourage your cat to eat the new food by offering extra incentives – treats mixed into the new food, a splash of tuna juice or chicken broth on top, or a sprinkle of Fortiflora powder – it is both a probiotic AND an absolutely addicting taste for most cats!


Now that you know the potential risks of diet transition, when to push through, and when to back off, and you have the ‘percentage rule’ stored in the back of your mind, you are ready to start the process of a diet change for your dog or cat. Your pet may have a very easy time or struggle with some of the side effects of the change, so keep working through the process with your pet’s specific needs in mind. When in doubt, remember that your veterinary team is a great source of information, aid, and support for your entire family as you work through this transition.