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

Figuring Out Food Sensitivities

Figuring Out Food Sensitivities
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“He has a sensitive stomach.” This is a common complaint heard in veterinary clinics. This phrase is typically used to refer to a pet that has frequent vomiting, diarrhea, or flatulence, especially when these symptoms are recurrent but relatively mild. Pet supply stores are full of solutions for this condition – diets marketed or labeled for “sensitive” pets as well as supplements abound. But are any of these products worth trying? What is the best way to approach your “Mr. Sensitive”?

One of the challenges of non-specific gastrointestinal signs like vomiting, diarrhea, and flatulence is that they can have many causes, both diet-related and unrelated. For diet-related issues, your pet could have an allergy or intolerance to a specific ingredient (although it is important to be aware that food allergies are uncommon!) or, more commonly, be reacting to other factors in the diet such as the amount of fat or fiber or the overall digestibility of the food. Many pets will have these kind of symptoms with a sudden change in diet, regardless of the properties of the diet itself.

Even if your pet otherwise is acting healthy and their symptoms are mild, it is worthwhile to have them evaluated by your veterinarian to rule out any specific health issues that could be causing the signs or contributing. Assuming everything checks out okay, there are some steps you can take to try to identify the cause of the symptoms and improve or resolve them.

  1. Keep a journal of the symptoms for a couple of weeks as a baseline, including an inventory of everything that you feed your pet. THEN:
  2. Eliminate all extras that you are feeding your pet – this includes dental chews, rawhides, treats, human foods (unless your pet is on a home-cooked diet), and any dietary supplements except those required to balance a home-cooked diet (check with your veterinarian first if they were prescribed to treat a specific health concern).
  3. Keep the main diet consistent – feed the same diet every day in the same amounts. Don’t rotate flavors. If you typically feed dry or wet food only, feed only 1 dry or wet diet. If you typically mix wet with dry, use only 1 dry and 1 wet and consider a trial feeding only wet or only dry.
  4. Continue to journal after you make these changes.

You should continue these steps for at least 2 times longer than your pet usually goes between episodes. So, if you pet usually has soft stool once a week, you need to be strict about the diet for at least 2 weeks to be able to determine if it is making a difference.

If your pet improves, great – you can try re-introducing the previous foods and extras and see if you can determine which are the issues (or if your pet is just sensitive to dietary changes in general). Keep your journal during this time to help you sort it out and introduce items one at a time and add only one new thing per week, allowing your pet to get back to normal in between if needed.

If your pet doesn’t improve and your pet’s symptoms are mild, it’s time to consider a diet change (if your pet is vomiting often, having frequent diarrhea, or acting ill, you should see your veterinarian). While there are many diets out there marketed as being appropriate for pets with “sensitive systems”, there are no regulations or necessarily even any consensus among manufacturers as to what this actually means. The most common meaning is that they contain fewer ingredients than other diets in the same line or they may contain ingredients that are exotic or less common – e.g. lamb or salmon or even venison or rabbit.

It is best to select a high-quality diet that has a short ingredient list as this decreases the number of variables. It’s okay to choose different ingredients than the current diet, but we recommend avoiding exotic ingredients. If you’ve been feeding a higher fat diet (many wet foods and many higher calorie dry foods), you can try one that is at least 25% lower. Keep in mind that you shouldn’t be comparing the “crude fat” on the labels directly between different diets, especially wet and dry, as this can be misleading. You’ll have to get the typical or average fat content from the manufacturer which should be on a “per 1000 kilocalories” or “per 100 kilocalories” basis, not percent. If the manufacturer can only give you the percent fat, use our calculator to make sure you are making these comparisons accurately.

Many pets may respond to fiber in the diet, but unfortunately, it is extremely difficult to compare the fiber content between diets as there are many types of fiber that can all have different effects on the gut and the amounts of fiber on the label are wildly inaccurate for most foods. The label reports only crude fiber, which is a measure of most of the insoluble fiber, but misses all the soluble fiber which can play a big role in gut health.

Once you’ve selected your new diet, introduce it gradually and give it a try as the only food that your pet gets, just like you did before. Keep your journal. If your pet improves,  then you can stay on that diet, or you can try to figure out what it was about the old diet that didn’t work so you know for the future.

If your pet doesn’t improve at all or gets worse, it’s time to talk with your veterinarian. Further diagnostic tests may be appropriate and the next step diet-wise may be to try therapeutic diets specifically designed (and tested) to be used in pets with gastrointestinal issues. This category includes diets designed to help diagnose food allergies or intolerance as well as diets with high digestibility and diets that are very low in fat (lower than is available over-the-counter).

While diet trials for pets with gastrointestinal disease are typically trial-and-error, your veterinarian can help you to narrow down a strategy and prioritize – should you try to test for a food allergy first, or is fat a more likely issue? Is your pet likely to benefit from fiber supplementation and if so, which kind? While it may take a few trials to find the best diet, you can reduce the time it takes by being strategic about your choices rather than just randomly trying various diets. A Board Certified Veterinary Nutritionist®   can also help you with this often-frustrating process of determining the best diet approach. And it’s important to realize that many dogs with chronic gastrointestinal issues require a combination of diet and medication to control their symptoms.

One of the biggest mistakes I see well-intentioned pet owners make is trying too many diets on their own haphazardly before seeking veterinary help. I’ve seen many pets that have been on over a dozen diets, sometimes for only a couple days at a time. This kind of diet history can make it that much harder to get to the bottom of things and can really limit the remaining diet options, resulting in an even more challenging process to control the pet’s symptoms.



Dr. Cailin Heinze is a Board-certified Veterinary Nutritionist® and the Executive Director and Chief Academic Officer of the Mark Morris Institute, a non-profit organization whose mission is to promote optimal companion animal health by providing educational opportunities for veterinary students and veterinarians in clinical nutrition. She has also done some consulting work for Balance IT, a company that makes software and supplements for home-cooked pet diets. She is an expert in home-cooked diet formulation and general pet nutrition and has a special interest in feeding pets with kidney disease and cancer.

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