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Canines experience food-related allergies that cause adverse effects to their physical health. Certain dog breeds are more prone to experience food-related allergies, which means that these allergies can be passed down genetically. Allergies can also develop as a product of a dog's environment, or due to a toxicity. The molecules that usually become allergens are intact proteins or glycoproteins. This is why it is important that hypoallergenic dog food diets offer a variety of protein sources that are unique. The strategy is to find and use proteins that are not recognized by the dog's antibodies as being antigens. This is done by adding novel protein sources, such as novel meats that a dog or its ancestors have never been exposed to. Another solution is to create your own "novel protein" by chemically modifying well known protein sources using hydrolysis techniques which render proteins unrecognizable by the gastrointestinal tract. However, not all antigens are specific to proteins, it is possible for anything that the body ingests to become an allergen, so it is important to provide diets with a limited amount of ingredients for diagnostic purposes as well as for dogs who are allergic to common ingredients used in pet food. It is also important that there are certain nutrients incorporated in hypoallergenic dog food, including omega-3 fatty acids, Vitamins A and E, zinc, novel carbohydrates, and fiber.

Allergen responses and symptoms
Allergens can elicit both immunologic and non-immunologic responses. Immunologic reactions, also known as Type 1 reactions are caused by the binding of ingested molecules to specific immunoglobulin E (IgE) antibodies. Once binding occurs, mast cell degranulation follows, releasing granules that initiate the symptoms of an allergic reaction in the body. These immunological reactions are almost instantaneous, and it is widely accepted that the molecules which bind to IgE antibodies are usually intact proteins. Non-immunologic, or non-IgE mediated reactions are less understood, but are known to present similar symptoms as immunologic reactions. These reactions can be classified under food sensitivities and it is argued that they are not truly allergenic. Whether a reaction is truly allergenic in nature or a sensitivity, it is important that hypoallergenic dog foods provide the ingredients necessary to keep canines from experiencing discomfort.

The symptoms of a canine food allergy or sensitivity vary greatly, but the most common to look for include rashes, swelling, itchy or tender skin, and gastrointestinal upsets. These symptoms are very similar to, but should not be confused with Canine Atopic Dermatitis, which is not caused by food allergies.



Hydrolyzed protein diets
One of the possible causes of food allergies in dogs is a reaction of the dog's immune system to the proteins in a diet. One method that may be used to try and combat this immunologic response in dogs with food allergies is the use of hydrolyzed proteins in the diet. Whole proteins are composed of single amino acids organized into a chain, which then interact in order to fold the protein into its final three-dimensional structure. Hydrolyzed proteins are whole proteins that have been broken down into smaller polypeptides through a process called protein hydrolysis. One method of protein hydrolysis involves the use of enzymes specific to proteins called proteases. Proteases act by cleaving or cutting whole proteins at specific amino acids within their structure in order to form multiple small polypeptides from a single whole protein. Different proteases are specific to different amino acids, and as such multiple proteases may be used in order to cut a protein at several different locations. The theory behind the use of these small peptides in food as an alternative to whole proteins is that their small size will prevent them from stimulating the immune system of the gut, thereby reducing and/or preventing an allergic reaction. When hydrolyzed proteins are used in hypoallergenic canine diets it is with the hopes of avoiding an immunologic reaction both in dogs that have consumed the whole protein previously and in dogs whose intestinal tract has never seen the whole protein before but has been known to react to other protein types.

Novel protein diets
Beef, soy, chicken, turkey and egg products are commonly used ingredients in commercial dog foods as a source of protein. These protein sources have been proven to elicit an allergic response in dogs with food allergies. Novel sources of protein can be used in place of these allergenic ingredients to meet the feeding requirements for a dog, while minimizing or eliminating the chances of an allergic response. For a protein to be considered novel, it must be one that the dog has not consumed before. Novel protein sources include venison, veal, kangaroo and fish, such as salmon.

Limited ingredient diets
Introducing a food that consists of limited ingredients is a common method of reducing the occurrence of food related allergic reactions in dogs. Limited ingredient diets are made up of fewer ingredients. This is an attempt to improve digestion and reduce the likelihood of a reaction ensuing in dogs with sensitivities to common ingredients found in most commercial dog foods. These diets will avoid protein and carbohydrate sources, such as beef, dairy, poultry, barley, and wheat. There are many feed ingredients that have been observed to predispose animals to diet related reactions. This is due to their frequent exposure to such ingredients, which makes it likely for them to adopt sensitivities and allergies to commercial dog foods. Studies have shown that it is possible for dogs to have symptoms caused by more than one ingredient in a given diet, this makes the use of a limited ingredient diet relevant as a result of the inclusion of single protein and carbohydrate sources. If symptoms of food allergies persist after the introduction of this type of diet, it can also be helpful for determining the new allergen that is causing the adverse reaction due to the limited number of ingredients. Although these diets consist of fewer dietary ingredients, they still provide all the necessary nutrients to meet the animal's requirements.

Omega-3 fatty acids
Essential n-3 fatty acids in dog food help to treat the inflammation associated with allergic reactions. These essential fatty acids help to manage inflammatory responses by changing the levels of pro-inflammatory and anti-inflammatory eicosanoids produced during a reaction. They also help to maintain healthy skin and to maintain cell structure. These n-3 fatty acids are usually incorporated into dog food diets by using ingredients like fish oil.

Vitamin A
Vitamin A is involved in cell growth and division, as well as hair growth and skin maintenance. Since some of the key symptoms of food allergies include damage to the skin, it is important to include Vitamin A in hypoallergenic diets to help clear up the damage done by any previous allergic reactions a dog may have had. Ingredients in dog food that function as a source of vitamin A are fish oils such as cod oil.

Vitamin E
Vitamin E is an antioxidant which has important functions in immune health. These compounds scavenge for free radicals, protecting cell membranes from damage caused by lipid oxidation. This is beneficial to have in hypoallergenic dog food diets to help maintain cell integrity in case damage does occur due to a reaction. Vitamin E is commonly found just as a vitamin supplement in diets, but it is also present in other food ingredients such as soybean oil, corn oil, olive oil, and sunflower oil.

Zinc
Zinc supplementation in hypoallergenic dog foods aids in the maintenance of skin and coat health. Zinc also plays a role in mitigating inflammatory and immune reactions. Zinc can be found supplemented as a mineral in the diet, but it can also be added in the diet through lamb meat, as this ingredient is known to be high in zinc.

Novel carbohydrates
Carbohydrates are large macronutrients which supply energy to the organism consuming them, and include nutrients such as sugars, oligosaccharides, and starches. Dogs may become sensitive or allergic to certain carbohydrate sources in their diet, and novel carbohydrates may be used in an attempt to avoid this reaction. Novel carbohydrates are carbohydrates which the dog they are being fed to has never consumed before. Some examples of novel carbohydrate ingredients include brown rice and sweet potato, as well as brewer's rice.

Fiber
Negative digestive effects that accompany dietary food allergies can be reduced by including insoluble fibers. Insoluble fibers have a relatively low fermentability, which help to decrease the negative digestive effects such as gas and soft stools. These fibers help to reduce gastric emptying in order to increase the time available for nutrients to be absorbed in the gastrointestinal tract. Compounds called fructooligosaccharides (FOS) are found in most insoluble fibers, which aid in promoting intestinal health. FOS act as a prebiotic to increase the growth of "good bacteria" and hinder the growth of "bad bacteria" in the animal's digestive tract. Common ingredients in dog food that provide insoluble fibers include beet pulp, cellulose and chicory root.