Fuzzypedia - Food Allergies

First of all, let’s talk about the baby elephant in the room. “Food allergy” is a debatable term. We could go back and forth about the differences between adverse food reactions, food intolerances, food hypersensitivities, and food allergies. But that would be very boring, and everyone but the doctors would probably fall asleep.

So, let’s just move forward on the assumption that when we are talking about food allergies, we are talking about foods that can cause symptoms of illness in your dog or cat. (I will return to this debate at the end of the article.)

Those Tests Don’t Work!

As we discussed in episode 3, Monkeys & Middle Schoolers, a simple test does not exist that will detect a food allergy in your pet, so put your wallet away before ordering Dr. X’s Amazing And Incredible And Totally Not A Scam Food Allergy Saliva Scan For Just $19.99.

That’s right, no saliva test, blood test, urine test, hair test, or any other kind of quick lab test is going to get us any closer to an answer. I wish these tests worked, but all reputable research studies on the topic have said that they do not.

No, this isn’t some kind of conspiracy laid out by big pet food companies. If the tests worked, we would use them. That would be way easier than what we do now. Remember, veterinarians are busy folks, and they want reliable answers as fast and efficiently as possible.

Why don’t the tests work? Good question! Typically, they measure your pet’s antibody levels to certain foods. The trouble is, animals produce antibodies to many foods, because the immune system has a process in place to distinguish between “self” and “non-self.” The bottom line is this: Just because your dog has made antibodies to a food doesn’t mean that your dog is allergic to those foods.

As an aside, I have read accounts of veterinarians submitting tap water rather than saliva for testing, only to find out that the tap water was allergic to a variety of foods. So...


The symptoms of a food allergy in your pet fall under two general categories:

1 - Skin issues: May include itchy skin, crusty skin, smelly skin, red skin, darkened skin, foot licking, hot spots (sores on the skin), itchy ears, and smelly ears.

2 - Gastrointestinal issues: May include vomiting, diarrhea, abdominal pain, and weight loss.

Dogs can have one or the other, or both issues.

The trouble is, a lot of other things can also cause skin and/or gastrointestinal symptoms. Since we don’t have a test that will tell us “positive” or “negative” for food allergies, we are stuck with good old fashioned logic. That’s where a diet trial (elimination diet) comes in.

The Elimination Diet

In order to check for a food allergy, a diet trial should be performed by feeding your pet a specially manufactured or cooked diet for at least 6 weeks.

During this period, your pet should not get ANY OTHER FOODS. No, not even one treat. And no, not even that rawhide. And no, not even your homemade peanut butter cookies, Martha. Remember, you are trying to help your dog and not flush your money down the drain. If your dog or cat eats anything else during the 6 week period, then you will need to START OVER. Ugh.

In order to perform an elimination diet, a prescription food from a veterinarian is typically needed. While you might be tempted to go out and buy an over-the-counter diet, studies have shown that cross-contamination is common in pet foods. For example, even if the ingredient list doesn’t say “chicken,” chicken proteins could have been present on shared manufacturing equipment, which allowed some tiny bits of chicken to make it into the food.

Prescription diets come in three varieties:

1 - Novel protein: An uncommon protein is used in these foods, such as rabbit, venison, or duck. Rabbit is my personal favorite starting point, since it is very rare, and it is unlikely that your pet’s immune system has ever been exposed to it before. This is what makes it “novel.”

​2 - Hydrolyzed protein: In these diets, a type of protein, such as soy or chicken, has been chopped up into tiny little pieces. The theory is that your pet’s immune system is less likely to react to these pieces of protein.

3 - Home-cooked: This is really a type of novel protein diet. You would choose an uncommon protein such as rabbit. Don’t just get a recipe off the Internet, though. They are notoriously out of balance. Check out www.balanceit.com instead.

Meat Your Maker

Meat allergies are uncommon in people, but they are relatively common in dogs and cats. Beef and chicken are repeat offenders. You’ll probably also realize that these ingredients are extremely common in pet foods.

I am often told by clients that they are feeding a high quality food, so the food couldn’t possibly be the problem. However, if your dog has a beef allergy, a $60 ribeye from the finest steakhouse in town would still cause problems.

Gluten, the protein found in cereal grains like wheat, is an uncommon trigger in dogs and cats.

So Itchy!

The most common reason a veterinarian will perform a diet trial is with an itchy dog. Once we have ruled out mites and fleas, we need to figure out if a dog has an environmental or food allergy.

Statistically, food allergies are uncommon. When considering all dogs with allergic skin disease, more dogs have environmental allergies (~85%) than food allergies (~15%). Around 5% of the same group of dogs have both food and environmental allergies.

So Gassy!

Here’s where the debate about food allergies vs food intolerances becomes slightly more important.

Diarrhea and vomiting are frequently caused by a particular food ingredient, but an allergic process is usually not taking place. This is where ingredients like dyes and preservatives come into the picture. Also, factors such as fat content can play a role.

Because an allergy usually isn’t present, a novel protein or hydrolyzed diet may not be needed to resolve your pet’s upset tummy. If your pet has the runs, but is otherwise healthy and energetic, then a simple switch to an over-the-counter diet may be all that is needed.

On the other hand, inflammatory bowel disease, which can lead to chronic vomiting, diarrhea, and weight loss, is often triggered by a dietary protein. Some pets with inflammatory bowel disease can see resolution of symptoms with a novel protein or hydrolyzed diet.

Technically, inflammatory bowel disease can only be diagnosed with a tissue biopsy from the gastrointestinal tract. But that’s a story for another day.

Final Thoughts

If you think your pet might have a food allergy, then talk to your vet. Getting to the root cause of your pet’s itchy skin or gastrointestinal problems requires a logical approach based on numerous factors beyond the scope of this article. Your pet’s history and symptoms are unique, so they need to be considered.

Neither Dr. Google, nor myself, will replace the professional skills and experience that a hands-on vet can provide. Ultimately, going to the vet will save you a lot of time and money, and Fuzzy will thank you for it.

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