Cat Food Allergies & Elimination Diets: Novel Protein & Hydrolyzed Protein Guide

Food Allergy vs. Food Intolerance

Many owners confuse food allergy with food intolerance, but the two have entirely different mechanisms. According to the Journal of Feline Medicine and Surgery (Verlinden et al., 2006),food allergy is an abnormal immune system response to specific food proteins, involving IgE antibodies or cell-mediated immune reactions;food intolerance does not involve the immune system and is typically related to enzyme deficiencies (such as lactose intolerance) or non-immune reactions to food additives.

The WSAVA Nutrition Committee notes that true food allergies account for approximately1–6% of all feline dermatological cases, but among cats presenting with skin symptoms, they represent about 12–21%.

Common Food Allergens in Cats

According to a systematic review in BMC Veterinary Research (Mueller et al., 2016), grain-based allergens are far less prevalent in cats than animal-based proteins. Therefore, "grain-free" food is not equivalent to "hypoallergenic" food.

Symptoms of Food Allergies

• Skin Symptoms: Head and neck pruritus, symmetrical hair loss, miliary dermatitis
• Gastrointestinal Symptoms: Chronic vomiting, soft stool or diarrhea, increased flatulence
• Ear Problems: Recurrent bilateral otitis externa, which may be the only clinical sign
• Eosinophilic Granuloma: Lip ulcers or skin plaques

AAFP emphasizes that food allergy symptoms overlap significantly with environmental allergies, but food allergies are non-seasonal and persist year-round.

Elimination Diet Trial Protocol

According to ISFM and the consensus of most veterinary dermatology specialists, the elimination diet trial remains the gold standard for diagnosing food allergies. Serum IgE testing lacks sufficient accuracy and is not recommended as a primary diagnostic tool.

1. Select a Trial Diet: Novel protein diet or hydrolyzed protein diet (see below)
2. Strict Compliance: During the trial period, only the trial diet may be given—no treats, flavorings, or other foods
3. Maintain Sufficient Duration: At least 8 weeks; some cats may need 10–12 weeks before showing significant improvement
4. Observe and Record: Document itching severity, skin condition, and gastrointestinal symptoms weekly
5. Provocation Test: After symptoms improve, reintroduce original food components one at a time to observe for recurrence

Novel Protein Diets

A novel protein is a protein source that the cat has never been exposed to before, such as venison, kangaroo, rabbit, or crocodile. According to AAFCO labeling regulations, the protein sources listed on commercial pet food labels must be accurate. However, research shows that some commercial "limited ingredient" diets have cross-contamination issues. A study in the Journal of Animal Physiology and Animal Nutrition (Ricci et al., 2013) found that some commercially available limited-ingredient diets contained undeclared proteins. Therefore, veterinary prescription-grade novel protein diets are generally more reliable than standard commercial products.

Hydrolyzed Protein Diets

Hydrolyzed protein diets use enzymes to break down proteins into very small peptide fragments (typically <10 kDa), making them too small to be recognized by the immune system, thereby reducing allergic reactions. According to a review in Veterinary Dermatology (Olivry & Bizikova, 2010), hydrolyzed protein diets have strong evidence supporting their use in the diagnosis and management of food allergies. Common veterinary prescription hydrolyzed protein diets include hydrolyzed chicken and hydrolyzed soy formulas.

Duration and Considerations for Elimination Diets

ISFM recommends maintaining the elimination diet trial for at least 8 weeks, as skin symptoms typically improve more slowly than gastrointestinal symptoms. During the trial period, keep the following in mind:

• All family members must cooperate and avoid secretly giving other foods
• In multi-cat households, feed cats separately to prevent stealing food
• Flavored medications (such as oral flavored dewormers) may also contain allergenic proteins
• If symptoms do not improve during the trial, discuss with your veterinarian whether to extend the trial or consider other diagnoses

References

1. Verlinden, A. et al. (2006). Food allergy in dogs and cats: a review. Critical Reviews in Food Science and Nutrition, 46(3), 259-273.
2. Mueller, R.S. et al. (2016). Critically appraised topic on adverse food reactions of companion animals: common food allergen sources. BMC Veterinary Research, 12, 9.
3. Olivry, T. & Bizikova, P. (2010). A systematic review of the evidence of reduced allergenicity and clinical benefit of food hydrolysates in dogs with cutaneous adverse food reactions. Veterinary Dermatology, 21(1), 32-41.
4. Ricci, R. et al. (2013). Identification of undeclared sources of animal origin in canine dry foods. Journal of Animal Physiology and Animal Nutrition, 97(s1), 32-38.
5. ISFM (International Society of Feline Medicine). Feline food allergy diagnosis guidelines.
6. WSAVA Global Nutrition Committee. Nutritional Assessment Guidelines.
7. AAFCO (Association of American Feed Control Officials). Pet Food Labeling Guide.