the scientific study of pet nutrition by veterinary nutrition specialists and experts.

How do I switch my pet’s food?

How do I switch my pet's food?
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How long should this take?

Unfortunately every pet is an individual and we’ve seen pets that can switch from one food at breakfast to another at dinner with no problems, while other pets require 4-6 week transitions to avoid stomach upset. To be on the safe side, like any big transition, it is best to introduce the new food slowly. We recommend gradually mixing an increasing amount of the new food into to the old diet for over the course of at least one week to allow your pet’s digestive tract the time to adjust. Just like humans, pets have a delicate digestive balance that is important for their overall health. By extending the transition over the course of a week, you allow your pet’s digestive tract to smoothly adapt to the new food.


What should I expect?

It should be noted that some soft stool can occur during a diet change. However, if your pet is experiencing an unusual degree of stomach upset, diarrhea, vomiting, excess gas, or constipation, that may be a sign that you are feeding too much of the new food too quickly or that the new diet is not a good fit for your pet.


What should I do if there are problems?

If you start to notice minor symptoms (loose stool, a little stomach gurgling), but your pet is otherwise acting fine, you can continue the transition, but stretch it out further. For example, if you noticed your pet had loose stool on day 3 when you got to 50% new food and 50% old food, then stay at the most recent ratio that did not cause issues for another day or two until symptoms pass, then continue with the transition.


When should I get worried?

If your pet has continued vomiting, liquid diarrhea, or appears painful or lethargic, call your veterinarian as there may be something else going on, your pet may be intolerant to an aspect of the food (fat, fiber, etc.) and she may need a different diet, or may need supportive care during the transition.


Is there a better way to describe what I’m seeing to my vet?

There are a few stool or ‘poop charts’ available that use a numbering system to help you provide your veterinarian with a better understanding of what you’re seeing in your pet. ‘Loose’ stool may mean something very different to different families and among different pets! {Link to stool chart}


How do I figure out how much to feed each day during the transition?

You’ll want to write down how many cups or cans of food you are feeding of the current diet and then look on the bag or ask your veterinarian how much of the new food your pet should get (hint: foods have varying calories so 1 cup of your pet’s old food may be much more or less than 1 cup of another food!). It’s ok to estimate to make life easier during the transition, too!



  DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7
Old Diet 90% 75% 50% 50% 25% 10%
New Diet 10% 25% 50% 50% 75% 90% 100%

Here’s an example as a guide to help out:

Let’s say you have a 12 lb cat that needs 250 Calories per day according to his veterinarian. Let’s do some math to see how we would switch from one food to another:

Old Cat Food Brand: 500 Calories per cup

New Cat Food Brand: 378 Calories per cup


We want your cat to get the same calories per day, so while he gets 1/2 cup per day of his old food, he would get 2/3 cups per day of the new food. How would we do this transition?


Example Transition

Old Diet 1/2 cup 1/2 cup 1/3 cup 1/4 cup 1/4 cup 1/6 cup 1/8 cup
New Diet 1/8 cup 1/6 cup 1/3 cup 1/3 cup 1/3 cup 1/2 cup 2/3 cup

You’ll notice the calories aren’t always the same everyday, and that’s ok for this one time transition, it’s more important to make sure the switchover is gradual than exact calories for a few days.


What if I’d like to be more exact in my measurements?

Instead of measuring by volume, you can always measure by weight! Many families buy a kitchen scale and then measure out their pet’s food in grams instead. Most foods will have calories (called kcal on pet food labels) per kilogram and then you can do the math to determine how many grams per day your pet needs.


Is it always best to mix the foods?

In particular, for some cats, it may be better to offer both the old and new foods side by side and let your cat make the choice. This may depend on whether your cat likes or avoids new foods. This could be a better option for cats that tend to get easily stressed or are sensitive to changes in their environment. If your cat doesn’t seem to like or try the new food, don’t despair, but remove it after an hour and then try again at the next feeding attempt always providing fresh food for each new feeding. Once the new diet is now familiar (it may take a few tries!) and your cat starts eating it readily, you can slowly decrease the amount of the old food in 25% increments until the change is complete.

More information on tips and strategies for feeding indoor cats can be found at the following educational sites for owners:,


Dr. Deborah Linder, a board-certified veterinary nutritionist, is the head of the Tufts Obesity Clinic for Animals and has had articles appear in Eating Well, the Boston Globe, AARP, SHAPE, and XM Sirius Radio Doctor Channel. She has spoken at national and international conferences and a Capitol Hill briefing, and is an expert in pet obesity, nutrition communication, and in the human-animal bond. 

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