What Is Hydrolyzed Dog Food? Effects and Selection Criteria

DigestiveQ&AMeongsiljang Veterinary Advisory Board

Hydrolyzed dog food is a specialized diet that breaks down proteins into very small particles to help reduce allergic reactions. We’ve outlined why veterinarians recommend it for dogs with food allergies or chronic digestive issues, along with tips for choosing the right product.

Hydrolyzed Dog Food: What’s the Difference?

An illustration of a puppy sitting next to a hydrolyzed diet food bowl

Hydrolyzed diets are special foods in which proteins are broken down into very small fragments, making it difficult for the immune system to trigger an allergic response. The proteins in regular pet food have large molecular sizes, which can cause the immune systems of pets with food allergies to recognize them as "enemies," leading to reactions such as skin itching, vomiting, and diarrhea. Hydrolyzed diets use enzymes to break these proteins into tiny peptides smaller than the size needed to provoke an immune response. Textbooks explain that these reduced-size proteins are unlikely to trigger immune reactions. However, depending on the type of protein source used and the degree of hydrolysis, some pets may still show reactions, so it's not accurate to say they always prevent allergies.

How Hydrolyzed Diets Work — Why Do Allergies Decrease?

Title: How Hydrolyzed Diets Work — Why Do Allergies Decrease? For the immune system to trigger an allergic reaction, protein molecules must be above a certain size. In studies of IgE-mediated food allergies in humans, it is known that allergenic proteins are primarily those with a molecular weight of 10 kDa (10,000 Daltons) or more. However, it has not yet been sufficiently confirmed whether this same molecular weight threshold applies to dogs and cats (Applied Veterinary Clinical Nutrition). During hydrolysis, enzymes break down proteins into smaller peptide fragments. These smaller protein fragments are less likely to be detected by immune cells, making it difficult for an allergic reaction to occur. That said, depending on the type of protein source used and the degree of hydrolysis, some hydrolyzed diets may still trigger allergic reactions. To put it simply, it’s like a large balloon being easily noticeable, but when torn into very small pieces, it becomes hard to recognize.

Which Pets Might Benefit?

Title: Which pets might benefit? Here are some common situations where hydrolyzed diets can be helpful.

Diagnosed or suspected food allergies: If a specific protein allergy has been confirmed or is suspected, hydrolyzed diets are often used during elimination diet trials.

Recurrent chronic vomiting or diarrhea: Veterinarians frequently recommend hydrolyzed diets when gastrointestinal symptoms persist despite feeding standard foods, due to gastrointestinal hypersensitivity or food allergies.

Gastrointestinal hypersensitivity-related conditions: Hydrolyzed diets may be incorporated into dietary management, at the veterinarian’s discretion, if gastrointestinal hypersensitivity is suspected or confirmed. Since chronic gastrointestinal diseases have diverse causes, it is important to determine whether to feed a hydrolyzed diet only after an accurate diagnosis.

Recurrent skin itching or otitis externa: Hydrolyzed diets can also be effective for skin conditions caused by food allergies.

If you suspect your pet has allergies, please review the Allergy Testing Guide first.

Illustration of a dog scratching its ears and an icon representing allergy symptoms

Regular Food, LID Food, and Hydrolyzed Food: What’s the Difference?

Here’s a clear comparison of the different types of pet food.

Category	Regular Food	LID (Limited Ingredient Diet) Food	Hydrolyzed Food
Protein Processing	No processing	No processing (single protein source)	Broken down with enzymes
Protein Type	Various mixed proteins	New single protein source	Broken-down proteins
Allergy Risk	Possible	Low	Very low
Purpose	Regular diet for healthy pets	Managing mild allergies	Severe allergies & diagnostic testing
Price Range	Moderate	Mid to high	High

LID foods use a novel protein source (e.g., venison, duck, kangaroo) that your pet has never eaten before, helping to avoid allergic reactions.

Do Not Change Food Without a Veterinarian’s Prescription

Hydrolyzed diets should be fed only under a veterinarian’s diagnosis and prescription. Changing your pet’s food without accurately identifying the cause of the allergy can make it difficult to pinpoint the true trigger. In particular, during an elimination diet trial, offering any foods or treats other than the hydrolyzed diet can render the results meaningless, so be sure to follow your veterinarian’s instructions.

Hydrolyzed Diets—Do They Really Work?

Title: Hydrolyzed Diets—Do They Really Work? Veterinary studies suggest that hydrolyzed diets are often effective when food allergies are the underlying cause.

Improvement in skin symptoms: Cases have been reported in dogs with food allergy–related pruritus or otitis externa showing clinical improvement after switching to a hydrolyzed diet. However, not all patients respond equally, and a lack of response to a hydrolyzed diet does not rule out a food allergy.

Relief of gastrointestinal symptoms: If chronic vomiting or diarrhea is due to a food allergy, symptoms may improve after transitioning to a hydrolyzed diet. The time required for improvement varies among individuals, so it is important to monitor progress over an adequate period under veterinary guidance.

Use in elimination diet trials: Hydrolyzed diets can be used in elimination diet trials to identify allergenic proteins. Because a lack of response to a hydrolyzed diet does not definitively exclude a food allergy, results should be evaluated together with your veterinarian.

Note that hydrolyzed diets may have limited benefit for gastrointestinal issues caused by factors other than allergies.

An illustration of a dog resting comfortably with healthier fur.

Criteria for Choosing a Good Hydrolyzed Diet

Here are the key points to check when selecting a hydrolyzed diet.

Check the molecular weight: The lower the molecular weight, the less likely it is to trigger an allergic reaction. If the product description includes molecular weight information, be sure to review it.

Type of protein source: Various protein sources such as soy, chicken, and salmon are used. A product based on a protein source your pet has never tried before may be safer.

Degree of hydrolysis: Some products are only partially hydrolyzed. For severe allergies, choose a fully hydrolyzed product.

Compliance with AAFCO standards: Verify that the product meets the nutritional standards set by the Association of American Feed Control Officials (AAFCO). Most prescription diets satisfy these standards.

Veterinary recommendation: The hydrolyzed lines from prescription diet brands are the most reliable in terms of clinical validation.

An illustration of a dog comparing ingredient lists on pet food packaging.

Points to Keep in Mind When Feeding

Title: Points to Keep in Mind When Feeding Here are some helpful tips to keep in mind when starting your pet on a hydrolyzed diet.

Transition Period Required: Switching abruptly from their current food can cause digestive upset. Gradually increase the proportion of the new food by mixing it with their old food.

Treats Must Be Controlled: During the elimination diet trial, no treats or human food should be given in addition to the hydrolyzed diet. Strict adherence to this rule is essential to accurately identify the allergen.

Maintain the Full Feeding Duration: For an elimination diet trial to diagnose food allergies, it is crucial to continue the diet without interruption until clear clinical improvement is observed. The duration is determined by your veterinarian based on your pet’s individual condition, so do not stop or shorten the trial arbitrarily.

Palatability Issues: The hydrolysis process can alter the taste, so some pets may initially refuse to eat it. If this happens, consult your veterinarian to explore alternative options.

If Digestive Symptoms Persist

Title: If Digestive Symptoms Persist If vomiting or diarrhea continues even after allowing sufficient time on a hydrolyzed diet, the cause may not be a food allergy but rather another condition, such as pancreatitis or inflammatory bowel disease. If symptoms do not improve, prompt further testing is necessary, so be sure to inform your veterinarian. For chronic digestive issues, you may also want to read about Symptoms and Dietary Management of Pancreatitis.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Should hydrolyzed pet food be fed for life?

Not necessarily. Once an elimination diet trial has identified the specific allergenic protein, you can switch to a diet that simply avoids that ingredient. Please consult with your veterinarian to develop a long-term feeding plan.

Why is hydrolyzed pet food more expensive than regular pet food?

This is because the process includes hydrolysis, which breaks down proteins using enzymes, as well as the costs associated with prescription-specific quality control and clinical trials. As a result, it can cost two to three times more than regular pet food.

Won’t feeding a hydrolyzed diet cause nutritional deficiencies?

Prescription hydrolyzed diets are formulated to meet the nutritional standards set by the Association of American Feed Control Officials (AAFCO), so you don’t need to worry about nutritional deficiencies. However, if your pet is on this diet long-term, please have their health regularly checked by a veterinarian.

What should I do if my dog refuses to eat hydrolyzed diet food?

The hydrolysis process can alter the food’s taste and aroma, which may reduce its palatability. To help, try mixing in a small amount of lukewarm water or combining it with a wet hydrolyzed diet from the same brand. If your pet still refuses to eat it, consult your veterinarian for recommendations on alternative products.

Can cats also be fed hydrolyzed diets?

Yes, we also have hydrolyzed diets for cats. The same principle applies to feline food allergies, so it's essential to use products specifically formulated for cats. Please proceed under the guidance of your veterinarian.

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References

[1] Applied Veterinary Clinical Nutrition, 2nd Ed — Chapter 8: Commercial and Home-Prepared Diets (Andrea J. Fascetti, Sean J. Delaney)

[2] Small Animal Internal Medicine, 6th Ed — Chapter: Adverse Food Reactions / Food Allergy

[3] Clinical Medicine of the Dog and Cat, 4th Ed — Chapter 25: Nutrition of the Critically Ill Dog and Cat

[4] Cave NJ. Hydrolyzed Protein Diets for Dogs and Cats. Veterinary Clinics of North America: Small Animal Practice, 2006; 36(6): 1251-1268