What is an adverse food reaction?

“An adverse reaction to food is an abnormal response to an ingested food or food additive.” (Small Animal Clinical Nutrition). When present, elimination diets can be useful to determine offending foods. 

This may be immunologic or non-immunologic. A food allergy is when the dog’s immune system incorrectly identifies a protein from food as harmful and launches an immune response. Ear and skin infections can occur as can puritis. Some dogs will experience vomiting or diarrhea. Food anaphylaxis is an acute response that can require emergency intervention. A common example of this type of reaction in humans would be a nut allergy- requiring immediate help. Food, plants, food additives, drugs, vaccines, insect bites and stings can all produce anaphylaxis. These are all examples of immunologic adverse food reactions.

Food intolerances describe a wide array of reactions to food- sometimes normal and sometimes abnormal. For example, consuming spoiled food and then developing GI distress is a normal nonimmunologic adverse food reaction. The decreased ability for a dog to tolerate dairy is also an adverse food reaction where there is a lack of adequate enzymes to digest lactose. Lactose intolerance is a nonimmunologic reaction- it is a metabolic food intolerance. A lot of unknown reactions fall under this term as well. 

What do adverse food reactions look like?



Adverse food reactions have no clear set of symptoms and symptoms can manifest across the board. They include but are not limited to papules (red bumps on the skin), erythroderma (reddened skin that can precede peeling), excessive licking or biting at the skin, hyperpigmentation (darkening parts of the skin), and seborrhea sicca (scaly flaky, itchy, red and dry skin). However, the location of skin disturbances can be of importance. Inflammation of the external ear canal where bacterial infections frequent should always be a red flag indicating potential adverse food reactions.


The GI can be damaged by food allergies. Diarrhea, abdominal pain, flatulence, soft feces, and increased elimination may be present with food allergies in addition to skin disturbances. A dog that has itchy skin, disturbed stool formation and increased elimination can strongly indicate that an adverse food reaction is the cause.

Now that we have roughly discerned the different adverse reactions to food, let’s shift gears and discuss abnormal reactions to food and how to determine the offending foods in the diet. Most commonly discussed in canine nutrition circles are the adverse food reactions that result in itchy, inflamed skin that can be seen with or without GI disturbances. It can be extremely difficult to narrow down the cause of these very general skin related symptoms because many things outside of the diet can result in similar symptoms. Environmental allergens and irritants- ranging from pollen or detergent used on blankets or beds- can cause the same itchy skin. Vaccine reactions can also cause similar skin disturbances. Before diving right into developing a plan, it is important to understand how these reactions occur so that you understand why elimination diets are important.

How do common adverse food reactions occur?

Allergies (Immunologic responses): Dogs with GI diseases including IBD have more food allergen-specific serum IgG than normal. This may reflect increased antigen exposure due to increased mucosal permeability. In other words, these dogs’ guts are unable to keep food particles where they ought to be and in addition, may have a hard time breaking down foods. This may be resulting in higher exposure to food antigens.

Food allergies can perpetuate IBD, but may not be the primary cause. Inflammation of the gut predisposes animals to acquire food allergies. When a novel ingredient is fed, we can see a decreased immune-mediated  inflammatory response but how long this lasts is questionable. This means that a novel ingredient can cause initial reduction in symptoms, but the poor gut health may not be fully addressed- leading to another round of adverse food responses. The duration of protein novelty to the gut associated lymphoid tissue (aka GALT) can be quite limited if the gut barrier is highly porous. Feeding changes can therefore help us manage the condition, but is not entirely addressing the underlying issue. However, these changes are important for beginning the healing process. During these times, avoiding foods that typically produce a lot of gas or high fat foods is critical for managing the symptoms in many dogs who are suffering from GI disturbances.

Breaking Down Food is Key. A Healthy Gut Barrier is Key.
Ingesting food requires a functioning immune system.  When you think about it, the digestive system is a long tube that is essentially outside of the body. The gut barrier and digestion in general helps protect the inside of the body from harmful substances that the animal intakes while also allowing beneficial and essential compounds in. A healthy gut barrier is absolutely essential for overall well-being. This gut barrier prevents the overwhelming uptake of food antigens- antigens being a foreign substance that induces an immune response. Optimal digestion is important because digestion breaks food down into small units that are less likely to cause a reaction. The barrier further protects from particles leaving the gut. However, even a healthy gut is not immune to larger particles passing through these defense mechanisms. When harmful compounds pass through the intestinal mucosa, the body is able to defend itself by removing them. When harmful particles arrive, GALT immediately responds to the potentially harmful substances. However, it is important that it does not launch an attack on food antigens. GALT must then “train” to recognize what is harmful and what is not. An immune system that launches an abnormal reaction to food antigens can result in allergic diseases. In summation, poorly digested food, increased intestinal mucosal permeability, age, inflammation, and disturbances in GALT response can play a role in adverse food reaction symptoms.
Nonimmunologic Adverse Food Reactions

There are other substances in food that can cause clinical signs such as histamine. It is worth mentioning that dogs (and humans) will have varying tolerances. Think of your dog as having a histamine bucket. Symptoms manifest when the bucket overflows with histamine- but histamine in the bucket contained does not cause symptoms. Histamine can be found in food, but is also made by the body and used in a myriad of functions including immune response. These guys can cause watery eyes, itching, and sneezing. Both enzymes and gut bacteria break down histamine in food, but it can be helpful to limit the amount of dietary histamine when the dog is dealing with allergic responses resulting in histamine response. Fermented foods, aged foods (like cheese), canned foods (especially canned fish), and prolonged storage of food in the fridge are higher histamine foods and should be limited for any dog struggling with histamine related issues. Perhaps a dog in the middle of winter can tolerate canned sardines, but when spring time allergies role around, the histamine levels get to be too much. For a dog undergoing elimination diets, low histamine is important to remember.

What Foods to Avoid

This is highly dependent on the dogs. Common foods that “cause” (though we know that this is often a symptom) an adverse reaction commonly include beef, dairy, chicken, lamb, and wheat. Though, it is important to note that any food or food additive has the potential to result in an adverse food reaction. Many tests used to determine offending foods (some better than others), are still not as useful as elimination-challenge diet trials.

Because gluten in and of itself can be a primary offending food, this is also something to consider when selecting foods for the elimination diet.

Dairy (yes, even raw goat milk) can be a popular food intolerance in dogs and likely should not be used in most elimination diets.

Food additives can cause adverse reactions. Parabens, dyes, and synthetic preservatives can be offending substances. Therefore, a homemade diet can be enormously useful as it allows you to control exactly what is in the food.

Elimination Diets for Dogs: Tell Me What Works!

Enough of the details- let’s discuss key points in developing a strategy for addressing adverse food reactions. A diet history of the dog will become incredibly useful in selecting novel (never fed before) ingredients. This may not be possible in all cases. In those circumstances, feeding less popular ingredients is likely a safer bet- so don’t reach for popular protein sources if the diet history is unknown.

Before Getting Started

If you are working with a dog with other serious health conditions or are working with a puppy, you should work with a professional. This guide is not for you. This guide will also not tell you how to use NRC nutrient requirements or other requirements since so much of that is available on my other website, www.rawfedandnerdy.com. Understanding nutrient requirements is really a prerequisite. That being said, the key points below certainly apply to raw feeders using ratios or other feeding methods.

Also, working with a veterinarian is important to help manage any other cause of GI or skin disturbances! It is not always food!

A food diary before getting started is also useful. Keeping track of what has been consumed and how the dog has done with different foods can be useful when constructing your elimination diet.

Flavored medications can also be a cause of an adverse food reaction. Work with your vet if these medications are required and see how they can support you and your dog.

It is important to also address the potential of skin and hair disorders unrelated to adverse food reactions. Fleas are an extremely common cause of skin disorders in dogs. Bacterial and fungal infections should also be investigated and a veterinarian will be essential. Zinc, copper, vitamin A, omega 3, omega 6, vitamin E are all key nutrients that can be short or unbalanced in a diet that may result in skin and hair disorders. For example, many raw diets are high in vitamin A, but can be low in zinc- which is needed for Vitamin A metabolism. Raw diets that utilize liver ingredients not rich in copper (chicken, turkey, pork liver) can cause changes in hair coloring and the ability to break down histamine. Furthermore, breeds can also be more susceptible to hair and skin disorders.

Meeting the Recommended Allowances

For those using nutrient requirements, adult dogs can go without meeting the RAs during initial elimination diets. It is important to consider potential pre-existing nutrient deficiencies. For example, if the dog was fed a homemade diet consistently low in zinc, then it may be advisable to supplement zinc right away if the novel ingredients (discussed below) are quite low in zinc. Zinc, the fat soluble vitamins, selenium, and manganese may all be of extra importance when addressing a dog with symptoms related to the skin. It is quite common for zinc to be at suboptimal levels in homemade diets. As mentioned, zinc is required for the metabolism of vitamin A- also critical for skin and immune health (especially at the gut barrier!) so evaluate the dog and the diet at hand and determine what is of highest importance. Of course, any nutrient suspected of deficiency should be addressed, but not perfectly meeting nutrient requirements won’t be detrimental for otherwise healthy adult dogs. When foods that are not offensive are discovered, the diet can be slowly built to completion using foods first, then supplements.

When selecting supplements, avoiding animal or plant based protein additives is important and can reduce the risk of an adverse food reaction.

It is important that calcium is not forgotten. While some do elimination diets with RMB, I tend to reach for pure calcium carbonate. Whatever your method, be sure that adequate calcium is in the diet.

Cooked or Raw

An elimination diet can be done with cooked or raw. It is worth noting that cooked and raw diets are both digestible, but cooked is actually a bit more digestible than raw. Remember that digestibility greatly affects the amount of larger molecules that make it through the gut barrier. However, cooked foods also need to spend limited time in the fridge to control histamine levels. Many factors may determine whether raw or cooked is appropriate for the dog we are working with.

Choose Your Foods: Novel Ingredients

It is best to select a protein source that has not been used before. For example, if beef and chicken have been fed in the past but lamb has not, lamb can be a useful ingredient.

Some debate whether organ meats should initially be included in the first week of an elimination diet. I personally choose to include liver as soon as possible since liver contains nutrients that are important for proper immune function. For me, this greatly depends on the dog’s history. Many will only do “muscle meat” ingredients that are animal based.


The same applies to digestible carbohydrates. If rice has been fed in the past and oats have not, then cooked oats would be more appropriate. While many raw feeders may scoff at the idea of feeding a digestible carbohydrate, digestible carbohydrates can help lower the amount of animal based proteins in the diet which can be useful in an elimination diet. You do want to be careful to not add carbohydrates that contribute excessive fiber. However, some amount of carbohydrates can improve gut motility, stool formation, and elimination. A diet that does not have digestible carbohydrates will by default be higher in protein and fat. This may or may not be useful. For most dogs, carbs can be useful. Although there are certainly cases I have worked with where higher fat and higher protein was much better tolerated than any form of plant matter and this very much reminded me of Crohn’s disease in humans. In my work, these tend to be the exception to the rule. Really, the level of protein, fat, and carbohydrates will depend a lot on whether GI symptoms are present.


Omega fatty acids- both 6 and 3 are of importance. These fatty acids are the essential fatty acids. Performed omega 6 fatty acids can be found in organ meats and many animal products. Omega 3 is found in oily fish, fish oils, but also in certain parts of land animals. Fish, as briefly mentioned above, can contain compounds that contribute to allergy-like symptoms- especially canned. Therefore, if possible, it would be best to not start out with fish, especially because it can be difficult to formulate fish based diets. Even fish oils can cause an adverse food reaction.

Brain, from a reputable source, is rich in preformed omega 3 DHA which is needed for immune response resolution. DHA can also be found in dark meat of poultry (although often poultry is not a candidate for being a novel ingredient). You do not need to and often should not add these ingredients right away and feeding different parts of the muscle meat from animals will result in different fatty acid profiles. Omega 3 can also be provided from plant based sources, but their bioavailability is lower and they should still be a novel ingredient.

It is important that when adding lipids you do not add a lot of fish oil. While fish oil contains omega 3 and specifically EPA, higher amounts can mask the symptoms. It can also interfere with omega 6 metabolism. Omega 6, wrongly blamed for the root cause of inflammation, is actually critical for a healthy gut barrier. Interference of omega 6 metabolism can be detrimental to the gut and the skin because it is required in a tightly knit gut.


Once you have selected your novel protein, carb, and if needed lipid or other supplements, a journal should be kept. The dogs behavior, stool, skin, and breath should be monitored. Absolutely NO other foods should be fed. It is important that the process below be monitored so progress or regression is noted with the offending foods.

The Feeding Plan

Textbook guidelines generally state that the food formulation made above should be fed for 4-6 weeks and assess:

  1. If with 100% certainty all ingredients were novel and symptoms have not improved or become worse, then an adverse food reaction becomes less likely. It does not mean that leaky gut is absent.
  2. If partial improvement occurs, continue feeding for another 4 weeks. If partial improvement continues, this may be a food reaction in addition to something else non-food related. Initiate a challenge food. If a challenge food is fed and results in worsening of symptoms, adverse food reaction is likely. Remove food and re-initiate the process.
  3. If dramatic improvement occurs. Initiate a challenge food by adding an ingredient- building the diet. If signs worsen after challenge food, adverse food reaction is likely.

That being said, I have found these time frames to vary quite a bit. Often times we can see dramatic improvement or worsening of symptoms in as little as a week. Keep the process and end goal in mind. Never have I had to go a full 4 weeks.

As you start to build the diet and make progress, you can begin looking at healing the gut. It is very important, though, that the initial elimination-challenge trial be followed as it both allows us to determine the likelihood of an adverse food reaction and what the offending food may be. It also allows the gut to catch a break by removing offending foods. Once a foundation has been built, then you can begin looking at some of the tools we add to address the gut. These will often be highly specific to the dog and may include probiotics, proteolytic enzymes, bone broth, certain kinds of fats, and an herbal protocol.



Gut health

is important. Leaky gut means the body’s defense mechanism is compromised.

Diet History

Addressing the total diet history will give us information on what has been fed and potential nutrients that may be deficient or in excessive amounts.

Digestion Matters

Digestion is important. Getting food broken down lowers the antigen load

Narrow in on Symptoms

Looking at both GI and skin related issues can tell us more about the kind reaction and how we should build the diet.

Address All Possible Causes

Making sure to address ALL possible causes of skin and gut disturbances outside of food. This can include fleas, bacterial and fungal infections, and pre-existing nutrient deficiencies and excesses.

Select Ingredients Carefully

Building a diet of novel ingredients or ingredients less likely to cause a reaction is important for the initial elimination diet. This also includes avoiding fish ingredients initially and high histamine foods. It means avoiding gluten and dairy.

Make & Follow a Plan

To follow an organized plan based on timelines but also the dog’s reaction.

...And That Plan Only

Make sure to ONLY feed the diet- no other treats etc.

Follow Through with Challenge Foods

Challenge foods are important because it allows us to provide more nutrients from food and to not inaccurately determine offending foods.

Don't Stop at the Basics

Take care of the gut after building a solid foundation in nutrition