You’ve just discovered that your pet has allergies and you’ve been advised to do an elimination diet trial. But what exactly is it, and what results should you expect?
Elimination diets can be recommended by your veterinarian for a variety of reasons. An itchy dog that doesn’t seem to respond to medication or a dog with a multitude of gastrointestinal trouble are both examples of cases where a food trial is a good idea.
While the elimination diet is the best way to assess and help dogs with allergies, there is some misconception among pet owners about the process. In this article I will guide you through everything we currently know about the elimination diet for dogs. I’ll also explore different types of elimination diets to explain the science behind each.
Effectiveness of Elimination Diet
Food allergies can occur at any age, although young and old dogs seem to be over-represented in scientific literature. Food allergies can also occur suddenly in dogs that have been on the same food for years.
A properly performed elimination diet trial is the gold standard for diagnosing food allergies in dogs (1, 2, 3, 4, 5, 6). Studies show that elimination diet has over 90% success rate when it lasts at least 8 weeks (7).
A 2015 study of 209 dogs with adverse food reactions showed the following (7):
After 3 weeks – 50% of dogs showed no food allergy signs
After 5 weeks – 85% of dogs showed no food allergy signs
After 8 weeks – over 95% of dogs showed no food allergy signs
There are two other methods – serologic testing with blood samples and dermatologic testing with skin prick tests – but both are less reliable methods for diagnosing food allergies in dogs when compared to elimination dietary trial (8, 9, 10, 11, 12).
Food allergies are not terribly common in itchy dogs. If your pet is constantly itching, he’s more likely to have environmental allergies that outnumber food allergies in dogs (13). With a positive elimination diet trial this subset of itchy dogs can also be adequately treated with just the appropriate limited ingredient diet.
Summary: Elimination diet is the most effective approach we have today for finding what causes allergies in dogs. Statistically, itchy dogs are more likely to suffer from environmental allergies than food allergies.
Signs of Food Allergies
Signs that your dog has a food allergy or sensitivity can be variable. Most commonly dogs suffer from itchy skin and secondary infections, lesions and crusting (2, 14, 15). As per a quantitative study, many owners note there isn’t a seasonal component, but if there are concurrent environmental allergies, this may not be the case (16).
Often, but not always, itchy dogs with food allergies experienced most itchiness on their feet, ears and perianal/tail area (3). In general, seasonal or environmental allergies tend to be more localized to armpits, inner thighs and abdomens.
Less common symptoms of food allergies include dogs that present with non-itchy skin lesions or gastrointestinal issues such as diarrhea and vomiting (17, 18).
Summary: Most common food allergy symptoms include itchy feet, ears and tail area as well as infections, lesions and crusting.
Finding Allergens and Causes
Before you start an elimination diet to rule out a food allergy in your dog, it’s important that any other concurrent skin issues be diagnosed and treated first. This includes secondary fungal, bacterial, and parasitic infections including mites, lice and fleas (14, 19, 20).
Once secondary skin issues have been addressed and cleared, an elimination diet to better understand the underlying cause for the dog’s symptoms can be attempted.
Technically, food allergic dogs can be allergic to anything in their diet. However, studies have examined and found that the most common ingredients for dogs to be allergic to are chicken, beef, dairy, soy and wheat (3, 9, 14, 21).
Today, it’s very popular to blame grains for food allergies in dogs. However, it is untrue that ‘all grains’ are highly allergenic in dogs, and there is no evidence to suggest that. Primarily, pets are allergic to animal proteins – the most popular ingredient in dog foods.
Corn, rye, oats and other whole grains are less likely to be the offending ingredient than the protein sources in the diet. The only exception is the cereal grain wheat; although at 13% of dogs being allergic to wheat it’s still less commonly the offending ingredient than chicken (15%) or beef (34%).
Summary: Skin health problems must be ruled out before starting elimination diet. Grains are unlikely to cause food allergies in dogs, and most common allergens are chicken, beef, dairy, soy and wheat.
Rules for Success
The goal of an elimination diet is to alleviate the pet’s clinical signs, either itchy skin or gastrointestinal symptoms. It is important to remember that an elimination diet is a test. The test is performed at home, and the goal of it is to identify what foods the dog is sensitive to in order to avoid them in the future.
Elimination diets need to be very controlled in order to be performed correctly. The diet trial should last at least 8 to 10 weeks to ensure success, with nothing else in the diet for the specified meal for the whole period – no treats, goodies, table scraps, flavored medications or supplements, or dental products (3, 15, 21, 22).
Things that you don’t even expect to interfere can completely alter the course of the trial. For example, a 2014 study published in the Journal of the American Animal Hospital Association showed that a once monthly heartworm preventative flavored with beef and soy can be enough to make a soy allergic dog symptomatic (22).
The elimination diet is often difficult for pet owners to perform on their dogs, but without following these very strict guidelines it will be impossible to determine what the dog is reacting to. Ensuring the dog has no access to the cat’s food, or the litter box, or any offending ingredients outside is also important.
Summary: Elimination dietary trial must follow strict rules, and continue for at least 8 weeks to ensure success.
Three Ways to Do It
There are three types of diets that can be considered appropriate to ensure a correct elimination trial for dogs. Remember that simply switching from one brand of dog food to another is not the right way to rule out food allergies.
Many dog food brands use the same main ingredients, including chicken and beef, because these are excellent sources of nutrients and protein for pets. Switching from one brand to another doesn’t necessarily eliminate or narrow down the ingredients being fed.
1. Hypoallergenic dog foods
One option for a correct dog food elimination trial is to feed a commercial diet meant specifically for food allergies (7, 9). These diets have typically one novel type of protein and one novel carbohydrate. A classic example is Lamb and Rice dog food recipe. There should be nothing else.
It is important, however, to use a diet designed specifically for food allergic dogs. Many brands claim the diet is lamb and rice, but upon closer examination of the ingredients listed, there may be other protein or carbohydrate sources added as well.
This isn’t an indication of a poor diet for all dogs; it’s merely an indication of a diet not appropriate for an elimination trial.
Another potential problem with commercial diets is that many brands will manufacture more than one diet in the same plant. Therefore, they are unable to guarantee that due to processing equipment being shared there may not be some cross contamination with a diet that does contain a more allergenic ingredient (5, 9, 22, 23). While it’s a viable option, over-the-counter commercial dog foods may not always be effective (24, 25).
There are a handful of non-prescription diets available over the counter that do a good job of pairing one novel protein with one novel carbohydrate (26, 27). Natural Balance, for example, certifies their hypoallergenic diets are manufactured in plants free from other allergens and ensure the ingredient list is limited.
There are also many veterinary prescription allergy diets available for elimination trials (5). These typically have to be purchased through a veterinary office and tend to be more expensive than over the counter dog foods.
The benefit of using a commercial diet (prescription or over-the-counter) for an elimination trial is the convenience of dry kibble. That said, it still needs to be fed as the sole source of calories for 8 to 10 weeks, with no other additives in order to be a true elimination diet for dogs.
2. Hydrolyzed dog foods
Another option for elimination diets to rule out food allergies in dogs is to use a hydrolyzed diet (28, 29). A hydrolyzed diet is available only as a prescription through a veterinary clinic and current scientific evidence regarding these diets is very promising.
The science behind a hydrolyzed diet is that the allergenic ingredients are rendered so small at a molecular level that the body doesn’t recognize them as allergens (30, 31). These diets have the convenience of being in a kibble form, but the downside is usually the hefty price tag that goes along with it.
3. Homemade dog foods
The third option for a well conducted elimination trial for dogs is going the homemade dog food route. The basic rules still apply: you pair one novel protein source with one novel carbohydrate source. For example, you might try venison and potatoes.
Note that contrary to popular belief, providing a nutritionally balanced home cooked dog food diet for long term use is not as simple as grilled meat and veggies. Dogs have very specific requirements for vitamins and minerals that cooking simple ingredients at home won’t provide. Home cooked diets over time can lead to mineral deficiencies if not properly balanced (32).
A short term 8 to 10 week elimination trial with a home cooked diet, however, is perfectly acceptable. Many veterinary dermatologists actually prefer this method over other elimination options because it allows you, the pet owner, to have complete control over what is consumed by your dog (33).
Summary: Using real hypoallergenic foods with novel protein and carbohydrate source is the most common way to approach elimination diets. Some commercial allergy food brands may be contaminated. Hydrolyzed foods are good but can be expensive. Homemade dog food can be used, but only short-term for the duration of the trial.
Once you have determined that the limited ingredient diet has eliminated the allergy symptoms in your dog, then ingredients can be added back in weekly. Typically, allergy symptoms in dogs will return within 24 to 48 hours after being challenged, although the non-itchy skin lesions may take 7 to 10 days (34, 35). Observe your dog closely at this time.
Expect that it will take some trial and error to formulate the clearest picture of what ingredients your dog should avoid. After the diet has been started, allergy symptoms usually lessen within 3 to 5 weeks, and go away completely at 8-10 weeks (5, 6).
For those cooking at home, you can choose to continue to preparing a homemade dog food diet by yourself, but for long term use, it is important to work with a veterinary nutritionist to balance the diet and provide essential nutrients and minerals (32).
When the offending ingredients are isolated, (for example, soy or dairy), then you can carefully select a commercial dog food that doesn’t contain these ingredients. In my practice I often see dog owners who found that the thing their dog is reacting to is actually a brand of dog treats or rawhide chews.
Summary: Symptoms begin to disappear in 3-5 weeks time. After the trial is finished, ingredients can be added back in weekly and the dog must be observed for symptoms to reappear.
In conclusion, it must be understood that elimination diet for dogs to diagnose food allergies is just a test. It’s the gold standard for allergic pets, and has a high 95% success rate in helping owners diagnose and eliminate allergens from the dog’s diet.
The trial must be performed properly using novel protein and carbohydrate source, and under strict rules. No other sources of food such as table scraps, treats, raw hides, flavored supplements or other pet’s food can be used.
It must be continued for 8 to 10 weeks to be successful, and all other secondary skin infections must be treated first.