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Ask Your Vet: Food Allergies by Stefanie Wong, DVM
November 19, 2014

Can I stop my pet’s itching by changing their diet?

It’s that time of year again, where allergies are at their worst and pets are itching, licking, chewing, biting and scratching non-stop. For pets with seasonal allergies, flare-ups are often seen twice yearly – in the spring and again in the fall. Although we are in the homestretch for dogs and cats with environmental allergies (whose itching will subside once the leaves fall off the trees and temperatures fall), dogs and cats with food allergies will continue to itch well into the winter and often year-round.

Allergies are, no doubt, one of the more frustrating things we see – for the pets, who are constantly itching and uncomfortable, for the owners, who are kept awake by the itching/chewing and find themselves visiting the veterinarian over and over again, and for veterinarians – because it’s not a simple fix. It often requires detective work on our part to figure out what type of allergy your pet has (if not multiple) and what the best treatment for them is (all dogs and cats are individuals after all). As you may know, allergies are often caused by one of three things:

1) Fleas

2) Food

3) Environment

For an overview of allergies and the strategies we use to treat them, you can read more here.

The most treatable conditions are 1) pets that just have a flea allergy (we simply place them on an effective flea preventative) and 2) pets that just have a food allergy (we simply switch their diet). That being said, it is not uncommon for pets to be affected by more than one of these (some are unlucky enough to be allergic to all three). In this article I will be going into more depth about food allergies and why we may recommend switching your pet’s diet when they come into us itching and scratching.

Why owners often don’t think to blame the food (common misconceptions)

Fiction: If my pet was allergic to the food, I should be seeing stomach upset (diarrhea or vomiting). The fact that they don’t have these things means they don’t have a food allergy.

Fact: In a lot of pets, we will only see itching and scratching – often centered around their head, face and neck. Some pets with chronic ear infections actually have low grade food allergies.

Fiction: My pet has been on the same food since they were a puppy or kitten. The fact that they are just starting to itch now means it must be something else.

Fact: Think about human allergies. Very commonly, as children we will not have symptoms of allergies – we pass through the seasons allergy-free. However, once we get older, we all of a sudden start to develop sneezing, running noses and itchy eyes. Pets are the same. It takes time for allergies to develop.

Recommended diets

Pets with allergies respond best to one of two diets:

1)      Hypoallergenic diets – also known as novel protein diets, these are diets that focus on a single meat source and a single carbohydrate source – our goal is to find a protein that your pet has never eaten before, which often means we’re reaching for more exotic proteins, like venison, duck or rabbit. Often the carbohydrate source is potato, as we do want these diets to be grain free.

  • Protein sources to avoid: Beef, dairy or wheat account for 68% of dog food allergies. Beef, dairy and fish account for 80% of cat food allergies.
  • Recommended: Royal Canin Hypoallergenic, Hill’s D/D

2)      Hydrolyzed protein diets – these diets focus around the concept that if you break down the protein into small enough pieces the body will not react to them

  • Recommended: Hill’s Z/D


Important note: Grain free diets have recently become very popular – almost all the pet food companies have hopped on the bandwagon, which makes it seem like there are endless options to choose from. It is important to know that all diets are not created equal. Some companies will run their beef diet through the production line, and then right after that run their “hypoallergenic” diet. If your pet is truly allergic to beef, even this small amount of contamination may be enough to set them off. Prescription diet companies have a separate dedicated facility to produce their hypoallergenic diets to avoid this problem from happening, which is often why they are recommended first.


Common causes for treatment failure

Have you tried a food trial recently for your pet and found yourself discouraged? Here are a few reasons why it may not have worked.

  • The trial was not long enough.
    • Pets need to be on the diet for a minimum of 8 weeks (some dogs require 12-16 weeks). That means at least 2 months before we can call the diet a success or a failure.
  • Your pet was not on the diet exclusively.
    • While on the diet trial, your pet cannot receive any table scraps, human food, treats (aside from the kibble that they’re on), rawhides, or bones.
    • Live in a multi-pet household? It is very important that your pet cannot have access to the other pet’s food – solutions to this problem include separating them from the other animals at feeding times or placing the other pet on the same diet.
  • Your pet has an environmental allergy in addition to a flea allergy.
    • In this case, you will likely see a partial response/improvement but not a complete one.


If it works

If your pet is no longer itching or shows improvement on the diet, then it should be a life-long diet. If you want to be sure that it is a food allergy and that your pet truly needs to be on this diet long-term we can conduct a challenge study – meaning, we switch them back to their original diet. If they start itching/scratching again within 14 days, then we have diagnosed a food allergy.

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