What's Behind Your Dog's Itchiness and GI Issues?

Analysis by Dr. Karen Shaw Becker

pet food sensitivity

Story at-a-glance

  • Pets with year-round itchiness and persistent or occasional GI issues are often reacting to something in their diet
  • Food sensitivities in dogs and cats can be caused by foreign contaminants in ultraprocessed commercial pet food
  • If you suspect your animal has a food sensitivity, the first step is to determine exactly what foods he's reacting to
  • The next step is to introduce a temporary novel diet; preferably a homemade fresh food diet
  • Because each case of food intolerance is different, if possible, it's best to work with a veterinarian with experience creating customized healing protocols

Pets with environmental allergies tend to suffer in the spring and fall, but many canine companions are itchy regardless of the time of year. If this describes your furry family member, it's very likely that something in his or her diet is the culprit.

Because most allergies in pets, regardless of the source, tend to manifest in itchy, inflamed skin, it can be difficult to know initially whether an animal has an environmental (seasonal) or food allergy. It's also important to understand that while the term "food allergy" is commonly used, true food allergies in pets are much less common than food intolerances or sensitivities.

Dogs and cats with sensitivities to something in their diet typically have symptoms such as itchy skin, skin and ear infections, and sometimes, vomiting and diarrhea. Unlike humans and cats, who almost always have gastrointestinal (GI) symptoms when they consume reactive foods, dogs are much more likely to develop skin problems first. There are certain clues that your companion's allergic symptoms may be food-related, including:

  • He's young — under 6 months — or his symptoms didn't appear until he was over 6 years old
  • Her breed is prone to food intolerances
  • He has sores or skin damage around the neck area, especially under the collar, and his whole head is itchy
  • She has received steroid therapy for allergies (which I don't recommend), but the treatment hasn't provided long term relief
  • He has intermittent gastrointestinal symptoms

If your animal is experiencing digestive issues such as vomiting, diarrhea, or constipation, it's important to recognize that these symptoms are also common symptoms of inflammatory bowel disease (IBD) or a leaky gut (dysbiosis), which can predispose pets to food sensitivities, and aren't always indicative of an intolerance to a particular food or ingredient.

Pets with GI inflammation from any cause often have concurrent food sensitivities, and vice versa. To effectively improve these patients long term, both conditions must be managed simultaneously to achieve improvement. Working with a functional medicine vet that understands your pet's dysbiosis and food sensitivities can yield the fastest results.

How Food Allergies and Intolerances Develop

When your pet has a true food allergy, his gut immune system (gut-associated lymphoid tissue, or "GALT") incorrectly perceives that something in his diet is attacking his body. To deal with the "threat," the immune system reacts by launching a counterattack just as it would against a real, infectious danger and produces IgE antibodies that result in a massive inflammatory response, making your pet miserable.

When your pet has food sensitivity or intolerance to a compound or ingredient in their food, the inward response can be the production of IgA or IgM antibodies, but the outward symptoms (skin and GI issues) can be identical to a true food allergy.

Certain substances in the diet are more likely to trigger symptoms than others, and unfortunately, the nutrient your carnivore needs most — protein — can sometimes be the culprit.

Although no research has been published on why carnivores may react to protein (the bulk of their ancestral diet), integrative vets agree foreign contaminants in factory-farmed animal products may be the culprit. Growth hormones, antibiotics and chemical residues may be the inciting triggers for leaky gut, which can set the stage for abnormal immune reactions to occur.1

If we had multiple generations of pets raised exclusively on organic, clean, fresh, species-specific diets, we could conduct studies to determine if they also develop sensitivities to meat proteins. If this population of animals did not develop intolerances to the proteins in their diet, our suspicions about foreign contaminants would be confirmed.

However, since 99.9% of pet foods are made with conventionally raised, factory-farmed meats (and only the leftover, rendered pieces and parts), blended with glyphosate and mycotoxin-contaminated grains known to disrupt the microbiome,2 sensitivities will continue to be an issue for almost all susceptible pets.

And to compound the problem, often it isn't until the GI tract has been significantly compromised by the inflammation caused by a reactive food that a pet begins to show symptoms of digestive dysfunction.

Animals fed the same food day in and day out for a period of months or years can develop a sensitivity to not only the protein source, but to any ingredient in the food, including grains, legumes, vegetables and added food chemicals (dyes, preservatives, emulsifiers, etc.).

If the food is made from inexpensive feed-grade raw materials (which describes most of the pet food on the market) and is highly processed (kibble is cooked 4 times before reaching the bag),3 the food contains high levels of advanced glycation end products, which also trigger the immune system to overreact.4

Figuring Out Which Foods Are a Problem

The first thing I do with pets over one year old who may have food sensitivities is complete a NutriScan saliva test. If the first thing your own veterinarian recommends is antibiotics and/or steroids, I suggest you order a NutriScan test yourself. I also suggest finding an integrative veterinarian who will work with you to identify the root cause of your pet's condition and develop a customized gut and immune recovery protocol.

The NutriScan panel tests your dog's sensitivity to 24 purified food extracts that recognize 56 food ingredients:

(bison, buffalo)

(chicken fat, necks,


(soy isoflavones)

(pork fat)


(deer, elk, treats/chews)

(barley water)


Sweet potatoes

(salmon oil)


Hen eggs
(fertilized hen eggs)

(wheat germ meal)



(lamb dairy, goat, goat dairy)

(peas, pea fiber, pea protein)

(cornstarch, corn
gluten meal)

(turkey necks, turkey fat)

(peanut oil)

Cow milk
(cow dairy)

(duck fat)

White-colored fish
(white-colored fish oils, herring, sardines, tuna)

NutriScan test results can often identify the specific ingredient(s) in your pet's food that are causing a problem, which makes it much easier to customize a diet to resolve the issue.

Introducing a Novel Diet

When a dog is having a reaction to something in her diet, her body needs a break from that food. After determining your dog's food intolerance(s) with a NutriScan test, my recommendation is to introduce a novel diet to promote healing. This means transitioning her to a different food she isn't sensitive to made up of ingredients her body isn't familiar with.

Unfortunately, many dog foods claiming to contain "novel proteins," don't. In addition, pet food mislabeling is a widespread problem, so if you're planning to go with a commercially available processed novel diet, be aware it will undoubtedly contain ingredients you're trying to avoid.

Because we don't have a way to quantify a pet's reactivity to the mycotoxins, pesticides, dyes, chemical preservatives and AGEs found in the vast majority of ultraprocessed pet foods, the very safest approach, especially for the first few months, is home prepared meals that allow you to control virtually everything that goes into your animal's mouth.

The second best option is a human grade commercially available fresh food containing an uncommon protein, produced by a company you trust.

It's very important that all foods your pet reacts to be avoided for at least 2 (and preferably 3) months, including previously fed treats. Animals often experience a reaction to both the primary protein and carbohydrate sources in their diet.

In addition to avoiding all problem foods, it's important to reduce or eliminate any filler ingredients and synthetic nutrients that can play a role in food sensitivities and inflammatory conditions. Meeting this criteria for a successful food trial can be difficult when looking at commercial pet food options.

I also believe pets with food intolerances do best on a very low-starch diet. Starch (which are soluble carbohydrates) are pro-inflammatory to the body and can exacerbate small intestine bacterial overgrowth (SIBO) and dysbiosis. Microbiome expert Dr. Holly Gantz has also seen beneficial changes in pets' microbiomes when carbs are reduced.

Until new labeling standards are fully in effect, pet food manufacturers aren't required to list carbohydrate content on their labels, so you have to calculate it yourself. It's worth taking the time to do this before choosing a novel diet (less than 20% carb content is the goal). Wean pets onto the trial diet slowly to avoid more GI upset. The day they eat 100% new food is day 1 of the food trial.

Reintroducing a Regular Diet

A dog with food sensitivities should remain on a novel diet for a minimum of eight weeks (once fully weaned onto the new food) and preferably 12 weeks, to allow the body time to clear out the allergenic substances and begin the detoxification process.

During this 3-month period I also work to resolve dysbiosis (leaky gut syndrome, which results from the inflammatory response in the GI tract) with microbiome restorative therapy and nutraceuticals necessary to address the root cause of the problem. This is where partnering with a functional medicine veterinarian with experience healing dysbiosis is important.

Because each case of food intolerance is different, again, I recommend a custom formulated protocol created by a professional who understands your pet's unique circumstances. Many "cookie cutter" leaky gut and/or allergy protocols aren't particularly beneficial and can even exacerbate symptoms because they aren't a good fit for the patient's specific issues.

With a classic food trial, a patient completes 2 to 3 months on a novel diet, then other foods are slowly reintroduced one at a time, and his or her response is closely monitored. In real life, most pets show dramatic improvement on the new diet, and in those cases, I typically don't rush the reintroduction of food that could be problematic.

This is when you can look for a human grade commercial diet made with the same novel protein, if you no longer want to prepare your pet's meals at home. If you decide to continue feeding a homemade diet, it's very important to follow a recipe that you know meets your pet's minimum nutritional requirements (most found on the internet don't).

Once a pet is stable and doing well, I encourage people to find at least 1 and preferably 2 other well-tolerated protein sources so that every 3 to 6 months they can rotate proteins and hopefully avoid future recurrences. Nutritional variety (rotating brands and protein sources) is one of the best ways to prevent food sensitivities from occurring in the first place.

In addition, I believe the cleaner the proteins, the less chance your pet will become sensitive to them over time. Clean animal proteins are less likely to create reactivity because they come from less toxic and less stressful environments. Wild caught, free range, organic grass-fed food production animals have a healthier diet and environment, so their meat has a better nutrient profile than animals raised in concentrated animal feed operations (CAFOs) or factory farmed.



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