Food Sensitivities/Intolerances Versus Food Allergies

(by Dr. Iuliana Mihai, DVM) 

Pet owners often worry that their pet has diarrhea, vomiting, or fur loss due to the food they consume. Although many times these clinical signs are associated with food allergies, they can also occur in food intolerances.  You may have even heard these two words used interchangeably, but there is a clinical difference between pet food allergies and pet food intolerances.

An intolerance is just a response of the digestive system to a particular ingredient in the food. A good example of food intolerance is lactose intolerance, which is experienced by the majority of adult cats. So, the old-fashioned idea of leaving a saucer of milk out for a cat is actually not always a great idea!

When it comes to food allergies, keep in mind that an allergy is a response of the immune system. A true food allergy involves the pet being exposed several times to the allergen ingredient until the clinical signs appear (as opposed to food intolerance when the clinical signs usually appear immediately after ingestion). In other words, immune system reactions generally require greater exposure to an allergen before the clinical signs can be observed.



Intolerance or Sensitivity

Involves immune system

Involves digestive system

Symptoms develop over repeated exposure to allergen

Symptoms appear almost immediately


Let’s explore each of these situations in detail:


Food Allergies

Food allergies or food hypersensitivities are a medical condition that commonly affects dogs and cats around the world. In general, diagnosing it is difficult and time-consuming for the veterinarian because food allergies don’t occur after ingesting only THE ingredient - the body can react to any ingredients found in a particular diet.


Common food ingredients that cause allergies in pets:


The ingredients that cause food allergies are called food allergens, with the most frequently reported food allergens being:


- Animal protein – from lamb (not so often), beef, chicken, chicken eggs, fish (especially in cats), or dairy products;

- Soy;

- Corn;

- Food additives: artificial colors, dyes, preservatives;

- Gluten.


And when it comes to diagnosing food allergies, although there are a multitude of techniques to diagnose them, the most popular method is to switch the pet to a completely different food than he’s used to. Then, by adding in ingredients from the former food, pet owners can observe which ingredient(s) trigger the intolerance symptoms.

Although this method is popular and easy, changing your pet’s diet can be complicated and might only address the problem partially. That’s because there is such a wide variety of ingredients on the market that are included in pet foods. For this reason, it is difficult to find a variety of foods (diets) that contain a single protein to which the pet has not yet been exposed.

Another explanation for the symptoms could be that the symptoms are actually caused by an illness. Inflammatory bowel diseases or other conditions, such as gastroenteritis, can make the intestinal mucosa permeable to some food proteins that are large enough to be allergenic. These disorders can make pets quickly allergic to a new source of protein.

Consequently, switching from a diet with an antigenic (allergenic) protein to another diet often fails to solve the diagnosis or the long-term maintenance problems that occur in food hypersensitivities.

According to researchers, it has been estimated that 15% of the total dogs in the United States suffer from allergies, 10% of them being food allergies.


Food Allergies Symptoms


When an individual's immune system identifies proteins as a potential intruder rather than a nutrient, an immune response is triggered, which most often manifests itself after an amount of time through gastrointestinal and/or skin reactions.

Skin reactions are most often represented by swelling, itching of the skin or ears (it can lead to skin and ear infections in the long run), including itchy feet (dogs usually lick their feet obsessively), fur loss and coat shine loss.

The gastrointestinal reactions are manifested through vomiting and/or diarrhea, abdominal cramps, gas, and others.

In the worst cases, anaphylactic shock with bronchoconstriction can occur, and sometimes it can be fatal, if not intervened quickly.

Some more unfortunate pets, especially dogs, can have both skin and digestive symptoms, making their lives even difficult, including their owners.

An unfortunate side effect is often having soiling accidents in the home. Many pet owners do not realize that their furry friend may be suffering from a medical condition and think that their pet is going through a period of bad behavior or separation anxiety. Because of this, some pet owners choose to scold or punish their pet, but the reality is that food allergens can be causing your pet a higher need to defecate – or defecating uncontrollably often due to diarrhea.


It’s not always just Allergies, there are other causes for gastrointestinal and skin problems in dogs and cats:

 Among the many causes of gastrointestinal problems in pets, the most common are caused by various pathogens such as viruses (parvovirus, coronavirus, etc.), intestinal parasites (tapeworms, roundworms), protozoa (Giardia spp.), bacteria (Helicobacter spp.), or various diseases, such as pancreatitis.

Skin problems can also be caused by various pathogens such as parasites (Demodex spp. - demodicosis; Otodectes cynotys - ear mites; fleas; ticks; dust mites), fungi, pollen, certain plants, or some diseases, such as hepatic diseases - they also cause, among other symptoms, itching, fur loss, etc.

Animals that show some of the symptoms mentioned above (or all) only when given a certain diet, may suffer from food allergies or food intolerances.


Diagnosing Food Allergies

When it comes to diagnosing food allergies, there’s no simple way to test for allergies, I’m sorry to say.

Although there are many tests on the market for food allergies in pets, they are not very accurate.

Many of them can give a false-negative or a false-positive result, meaning that healthy animals will test positive for food allergies and allergic animals will test negative. In many studies, researchers have concluded that these tests are not helpful, despite their widespread use to detect food allergies. Moreover, they also showed that many of them have a positive result (i.e. there is a food allergy) to plain water or artificial fur of plush toys.

The most popular method of diagnosing food allergies in pets remains the method of dietary elimination – changing the food systematically to rule out the ingredients causing the symptoms.

With this diet, the pet's symptoms should begin to decrease in intensity until disappearance. The diet will be purchased through a veterinarian or the vet will teach the pet owner how to prepare a homemade balanced one that contains only a few ingredients that the pet has never been fed with before - usually, a protein and a carbohydrate (and the necessary vitamins and minerals). Other variants are feeding the pet with hydrolyzed ingredients (i.e. the proteins are broken into small fragments that cannot be detected by the immune system) or purified ingredients.

Regardless of whether this diet is given by the veterinarian or homemade, it must be administered for at least one month, without consuming anything else. After this "trial" month, if the animal's symptoms have visibly improved, in order for the veterinarian to be able to conclude it was a food allergy, the pet must return to the previous diet and wait a while to see if the symptoms return. A rapid recurrence of the symptoms will suggest a food allergy to one or more of the ingredients in the old diet.

Many pet owners change their pet's diet on their own, and their symptoms improve, but they do not return to the old diet to test whether it was a food allergy or not.


The “Hypoallergenic Diet” Myth

You might have seen “hypoallergenic” veterinary diets on the market designed to reduce food allergies in pets. As it is known, there is no completely hypoallergenic diet - any type of diet can cause food allergies because, as we said, an animal organism can be allergic to any ingredient in a diet.

As for hypoallergenic diets, they are made from hydrolyzed ingredients - ingredients that are broken into small fragments that cannot be detected by the immune system – and have a low percentage of animal protein.


Diet Rotation

Many pet owners prefer to change the pet's food on occasion, believing that their pet is less likely to develop a food allergy if they aren’t exposed to the same combination of ingredients for very long. As others claim, there is no scientific evidence that this is true but on the contrary, this method limits future dietary choices if the animal suffers from a food allergy and needs to be diagnosed (through the dietary elimination method). In other words, the more often the animal's food is changed, the more difficult it is to diagnose a food allergy through the dietary elimination method. This happens because that pet has eaten a wider range of ingredients that could have been used for a potential diagnosis.


What to do if Your Suspect Your Pet Has a Food Allergy


It’s worth noting is that food allergies are more serious than food intolerances. Though you can “treat” food intolerances yourself by narrowing down the best food ingredients that don’t cause symptom, food allergies are a different story.


Here’s what to do if you suspect your pet has a genuine allergy to food:

  • Take your pet to the vet for a consultation – Your vet would want to know what is your pet eating and for how long; depending on your pet's symptoms, he/she will do some blood tests, parasitological, bacteriological, or fungal examinations, ultrasound, etc.
  • Do not change your pet's diet until you talked to a veterinarian.
  • Listen to your veterinarian - Do not give your dog or cat other food or any treats unless your vet says it is OK because you will ruin your dog or cat diet and the symptoms can relapse or get worse.
  • Treat your pet with love and care as always.



Dr. Iuliana Mihai, DVM, Masters In Small Animals And Equines Pathology

Iuliana graduated from the University of Agronomical Sciences and Veterinary Medicine in 2012, Romania. She has a Master’s degree in Small Animal and Equines Pathology and a strong affinity for Veterinary Parasitology and Laboratory. In 2013 she started her Ph.D. in epithelial cancer in dogs and cats. She volunteered at the faculty’s clinic at her 3rd year of study, and continued her career in small animal pathology and laboratory. She has one cat and eleven rats. Her interests outside of work include traveling, writing, and crafting.







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