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Food Allergies
Part 3 of a 3 part series

By Dr. Jean Hofve, Veterinarian Advisor


Interested in learning more? Check out the other two articles in the series!
Part 1: Overview of Allergies
Part 2: Understanding Inhalant Allergies
Part 3: Food Allergies

 

"Experts believe that between 10% and 20% of all allergies are food allergies."


 

A Brief Introduction to Allergies

An allergy is an immune system reaction to a specific molecule, which is called an allergen. Most allergens are proteins, but practically anything can become an allergen in any particular animal. In dogs and cats, the most common allergy is to flea bites; followed by “atopy” an allergy to inhaled particles such as pollen, mold, and dust mites.

The medical name for an allergy is a “hypersensitivity reaction.” There are four types of hypersensitivity reactions, but most of the allergies our pets are prone to are Type I or “immediate” hypersensitivity. This reaction takes place quickly; usually within minutes, but up to about 12 hours after exposure. An allergy to bee stings or flea bites are classic examples, but food allergies and atopy also fall into this category. Some allergies are very severe and can be life-threatening, though this is rare in pets.

The symptoms of allergies in pets usually appear in either the digestive system (vomiting and/or diarrhea) or the skin (itchiness, redness, lesions, hair loss, ear infections). It can be very difficult to distinguish atopy from food allergies; and some pets have both.

In this article, we’ll focus on food allergies.

 

 

Food Allergy Symptoms

Experts believe that between 10% and 30% of all allergies are to food. Food allergies are much less common than food intolerances. An allergy involves the immune system, while a food intolerance is a simple reaction to a food’s ingredients—often one or more of the colorings, texturizers, or 25 other categories of allowed pet food additives. Because they involve antibodies and immune-based inflammation, true food allergies are very different from dietary intolerances.

However, the symptoms are often the same: vomiting and/or diarrhea. These symptoms may be chronic or intermittent. However, the other major symptoms of food allergy that don’t usually occur with food intolerance are skin symptoms: itching, redness, rashes, hair loss, and ear infections. Just to complicate things, these symptoms can also occur with allergies that don’t involve food, such as flea bites and pollen, as well as non-allergic conditions.

This chart shows the symptoms most often seen with allergies and intolerances.

Table of Food Allergy Symptoms

Skin symptoms of allergy (referred to as “allergic dermatitis”) are frequently complicated and aggravated by secondary infections by yeast or bacteria. Additionally, these symptoms may not be related to food or allergies at all; there are many potential causes of digestive and skin issues. If your pet is having problems, please have your veterinarian take a look.

 

 

Differences Between Dogs and Cats

Cats are more apt to have food allergies than dogs. Some dermatologists believe that up to 50% of ear infections in cats are due to food allergies, but only 15% of similar infections in dogs.

Allergies typically develop over time and after multiple exposures to the allergen, although they are occasionally seen in young puppies and kittens, or after only one or two exposures. It’s common to think that if a pet has been eating the same food for years, symptoms couldn’t be due to allergies. But just the opposite is true: eating the same food over a long period of time is a recipe for allergy development. Not surprisingly, then, the most commonly used pet food ingredients are the ones pets most commonly become allergic to. For instance, meat by-products, liver, and meat-and-bone meal come largely from cattle, so allergies to beef are common.

Table of Common Food Allergens

The most common food allergens for dogs are: Beef, Chicken, Milk, Eggs, Corn, Wheat, and Soy.
The most common food allergens for cats are: Fish, Beef, Milk, and Milk Products.

Some animals have cross-reacting allergies; that is, if they are allergic to chicken, they are also allergic to turkey, eggs, and other birds; a beef-allergic pet may also react to other cloven-hoofed animals such as bison, venison, or lamb. Pets who have an allergy to one thing are prone to developing more allergies.

Comedian Chris Rock was once talking about friends whose child had food allergies, and asked, “How can anyone be allergic to food?”And that’s a good question! All animals must eat to live, so it doesn’t exactly make biological sense that the body would reject good nutrition, or react so badly to it.

One way that an ingredient can become an allergen is the heat processing that pet food undergoes during manufacturing. Heat can “denature” proteins, which means that it distorts their shape. Shape is how the immune system tells proteins that belong in the body apart from foreign proteins. When an abnormal protein is picked up by an immune cell, the whole system responds, and antibodies are produced. After that, every time that protein appears, antibodies flock to it and stimulate inflammation. The more damaged proteins, the more inflammation. When the offending allergen is in the pet’s everyday diet, the situation can become quite severe and uncomfortable for your companion.

The very fact that this reaction takes place at the lining of the gut causes changes in the lining itself. Swelling and inflammation cause the normally tight barrier of gut lining cells to become “leaky.” This “leaky gut” will absorb more things it shouldn’t, causing the reaction to move into the bloodstream, where it can cause inflammation elsewhere, notably the skin.

 

 

How Diet Changes and Supplements Can Help a Pet with Allergies

Fortunately, both food allergies and food intolerances respond to dietary therapy. This may be as simple as changing brands, since each manufacturer uses its own proprietary formulas and ingredients. Many food intolerances will disappear with any new food. Allergies are harder to deal with, but the treatment for food allergies also happens to be one of the simplest ways to diagnose them.

Changing your pet’s diet to a “novel ingredient” diet, also sometimes called a “hypo-allergenic” diet, allows the immune system to settle down and the inflammation to resolve. The new diet should contain protein and carbohydrate sources that the animal has not had before.

Here’s how to do a “diet trial” for food allergies:

  1. Choose a food that does not contain the same ingredients that were in the food your pet was eating when the allergy began. There are several ways to go:

    • Often, it’s best to start with a very simple home-cooked diet, such as plain turkey and white rice. For the short period of a food trial, it’s usually safe to skip supplements; a deficiency is unlikely to occur that quickly. However, work with your veterinarian to make sure your pet’s unique nutritional needs are met during this time. A pre-mix or a complete homemade diet are also great options if you don't have time to prepare a full meal at home.

    • Use one of the many ready-made commercial pet foods that can be used for a novel ingredient diet. Choose an unusual protein such as rabbit, bison, and duck, with a carbohydrates like sweet potatoes, brown rice, and green peas. There are veterinary diets for this purpose, but their ingredients tend to be poorer quality than a good natural food brand.

    • Change food forms, i.e., from dry to canned. There have been cases where an animal who reacts to a dry food does fine with the same brand’s canned version. Canned foods are processed at lower temperatures, and may be less allergenic.

    • Consider a raw diet. As with dry and canned foods, sometimes animals who are allergic to an ingredient in a processed pet food will readily tolerate the same ingredient in its raw form. However, in pets with leaky gut syndrome, the natural bacteria in raw meat may be a risk. You can lightly cook the food for a while until the gut has healed.


  2. In most cases, it’s best to switch diets gradually over a week or two. Cats are notoriously finicky, and it may take even longer for them. If your pet is willing to eat the new food right away, you can make the change faster, but be aware that digestive symptoms could get worse at first, because the gut has not had time to adjust.

  3. Feed exclusively the new food for at least 8 weeks. No cheating—no table scraps, no treats. Giving anything but the new diet will put you back to square one, and you’ll have to start the 8 weeks all over again.

    • When the symptoms are all gut-related (vomiting, diarrhea), improvement may be quite fast.

    • Skin symptoms may take up to 12 weeks to resolve, but there should be at least noticeable improvement within about 8 weeks.

  4. If the symptoms aren’t changing at all, you may need to switch to a different diet. Remember that allergies can cross-react, and that your pet may be allergic to more than one ingredient.

There are also several supplements that can be very helpful for allergies. These can be used independently or in conjunction with a diet trial.


  1. Digestive Enzymes help break food down into smaller particles, which will be less reactive in the gut. They also help “clean up” areas of inflammation.

  2. Probiotics are “friendly bacteria” that are important for gut function and health of the cells that line the digestive tract. They also have some anti-inflammatory properties.

  3. Omega-3 Fatty Acids (fish oil, cod liver oil). These essential fats are strong anti-inflammatories, and are also important for skin health.

It’s an interesting phenomenon that even pets who aren’t food allergic, often respond to a diet trial. The problem may actually be atopy, asthma, or any number of other inflammatory conditions. Simplifying the diet reduces the total number of allergens a pet is exposed, and that seems to help many non-allergic conditions, as well as allergies other than food.

Remember that allergic pets tend to develop more allergies—including to new foods. Lamb and rice was once a popular combination for allergic pets, but after eating it over a long period of time, many pets became allergic to lamb, too. If your pet is prone to developing allergies, it’s wise to switch foods (to different protein and carbohydrate sources) every 3 or 4 months to prevent future problems.

 

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