When dogs develop food allergies, they can experience uncomfortable, itchy skin as well as chronic conditions such as breathing difficulties, ear infections, and gas. An allergy is the immune system of the body responding to a perceived threat, in this case, brewer’s yeast. In order to definitively diagnose allergy and determine which allergen is causing your pet’s affliction, an elimination diet will be implemented. This can be a time-consuming process, but is necessary in order to deduce which particular ingredient is causing the reaction.

An allergy to brewer's yeast is an over-reaction of your dog's immune system to an unwelcome amino acid found in the brewer's yeast itself.

Canine food allergies can develop at any age, but the majority of dogs who acquire food allergies are three years old or older. Skin reactions are often located on or around the face, groin, under the front legs, or between the toes.

Food allergy - An allergy to food is a response by the white blood cells in the body’s immune system to protect itself against a protein that it views as a threat. An allergic reaction doesn’t happen upon initial exposure to an allergen as it takes multiple exposures to alert the immune system. Some foods, such as beef, chicken, dairy, and eggs are prone to cause allergies in dogs, although any food can become an allergen. 

Food intolerance -  Food intolerance has no immune involvement. It can have several core triggers, including missing enzymes in the animal’s system, toxins, and a natural occurrence of histamine present in the food itself, usually due to improper storage. Gastrointestinal symptoms, such as vomiting and abdominal pain are more common with food intolerance than with allergies alone. Additional symptoms, such as gurgling sounds from the digestive system and a change in the consistency or color of the stools are common with instances of food intolerance.

Allergies are an abnormally intense defensive response by the white blood cells of the immune system to an amino acid that the immune system considers to be an invasive substance. An amino acid is the product of digestion, food, broken down to its smallest parts. Around 60-70% of our immune system cells are estimated to reside in the digestive system where white blood cells called enterocytes absorb the amino acids and transport them to the bloodstream. When proteins are not properly broken down during digestion, the enterocytes see them as intruders and attack. The response of the immune cells become more aggressive over time, and the symptoms intensify. 

Brewer’s yeast has been used as a supplement for dogs for many reasons, including:

Allergic reactions are usually first apparent on the skin, and the symptoms that your dog will exhibit due to an allergic reaction will generally prompt your veterinarian to collect a skin sample from any affected areas to be used for a process called cutaneous cytology, which is a microscopic examination of the cells of the skin to uncover problems like external yeast infections, mites, or even signs of disease. When these types of disorders have been eliminated, a food allergy may be suspected. If brewer’s yeast was recently added as a supplement to the dog's diet and is believed to be the allergen, diagnosis may be made simply by removing the brewer’s yeast from the diet.  

If the core ingredient is not known, an elimination diet is usually implemented to confirm the presence of an allergy. Symptoms caused by an allergy will be extinguished during a properly executed elimination diet and once this has occurred additional ingredients may be slowly added back to the diet until the allergen is positively identified. During this diagnostic treatment, it is of utmost importance that your dog does not have access to anything ingestible other than the food chosen for the elimination diet. A single dose of the allergen can cause the allergy to resurface.

An elimination diet can take several weeks to uncover which allergen is responsible and during the interim, your pet may experience lingering  symptoms. Some veterinarians may recommend antihistamines to calm the itching as well as corticosteroids to reduce swelling. Use of these treatments may also mask the observable signs of allergy, making it harder to establish which ingredient in your dog’s diet is causing the reaction. Because of this many veterinarians prefer to complete the elimination diet before applying these types of medications. 

Additional supplements, including probiotic and Omega-3 oils, may be proposed as well to support the immune system after the elimination diet is completed. This will assist your pet’s body in handling any accidental exposure to allergens as well as helping to prevent the cultivation of new allergies. Secondary skin infections are commonly seen with food allergies, and antibiotics may be prescribed to combat this problem. Once the allergen has been identified, the initial course of action is avoidance of the ingredient.

Allergies to food are not curable, however excluding the allergen from the patient’s diet is usually sufficient to eliminate the symptoms. Brewers yeast is not a common ingredient in dog food and is generally given as a supplement in either pill, tablet, or powder form. Your veterinarian should be consulted before adding supplements into your canine’s diet, and introduction should be limited to a single supplement at a time. This will make it easier to diagnose the origin if allergies do develop. Dogs who develop allergies to brewer’s yeast may be predisposed to the development of new allergies, especially allergies to other types of yeast.