Food Allergies

Food allergy in dogs is an immune-mediated response to specific proteins in the diet. The most commonly implicated proteins are beef, chicken, dairy, wheat, and lamb - not because these are inherently allergenic, but because they're the most commonly fed proteins, so dogs have the most exposure.

True food allergy is distinct from food intolerance (a non-immune digestive reaction). Both can cause gastrointestinal signs, but food allergy typically also causes skin signs - itching, ear infections, and skin changes that are non-seasonal and don't resolve with environmental allergen management.

Diagnosing food allergy: the elimination diet

There are no reliable commercial blood or skin tests for food allergy in dogs. The only way to diagnose it is a strict dietary elimination trial:

1. Feed a diet containing a single protein and single carbohydrate source that the dog has never eaten before (novel protein diet), or a hydrolysed protein diet (where proteins are broken into fragments too small to trigger an immune response)
2. Feed nothing else for 8–12 weeks: no treats, dental chews, flavoured medications, rawhide, or table scraps
3. If signs improve significantly during the trial, it suggests food allergy
4. Re-introduce the original diet (food challenge) - if signs return, the diagnosis is confirmed
5. Re-introduce individual proteins one at a time to identify specific triggers

What to log during an elimination diet

The elimination diet is where a log becomes essential. Record daily:

• Itch score (0–10) - the target is a 50%+ improvement by week 8
• Ear status - better, same, worse
• Stool quality - food intolerance often causes loose stools that improve on the elimination diet
• Exactly what was eaten - every meal, every treat, every scrap from the table or floor
• Date any new item was introduced (during the re-introduction phase)

Any break in the diet resets the clock. A single piece of toast fed halfway through the trial may explain why signs didn't fully resolve. The log is the evidence.

Year-round vs. seasonal itching

Food allergy causes non-seasonal symptoms - the same level of itching year-round, regardless of pollen count or season. If itching is clearly seasonal, atopic dermatitis is more likely. Many dogs have both.

Year-round itching that doesn't respond to environmental allergen treatment (Apoquel, Cytopoint) is a signal to investigate food allergy.

Food choices during the trial

Options for the elimination diet:

• Novel protein commercial diet - commercially prepared food using a protein the dog hasn't had before (duck, venison, rabbit, kangaroo, salmon) paired with an unfamiliar carbohydrate
• Hydrolysed protein diet - a prescription diet (Hills z/d, Royal Canin Anallergenic, Purina HA) where proteins are broken down below the threshold for immune recognition

Avoid over-the-counter "hypoallergenic" foods - many contain trace amounts of common proteins from manufacturing lines. Prescription diets have better manufacturing controls.

When to contact your vet

Contact your vet for a routine appointment to:

• Plan a dietary elimination trial (which diet to use, what to watch for)
• Review progress at week 6–8 of the trial
• Discuss re-introduction protocol once the trial period is complete

Contact promptly if:

• Skin infections are developing or worsening during the trial
• Your dog is not eating the elimination diet and losing weight

Frequently Asked Questions

How long does a food elimination trial take? 8–12 weeks minimum. This allows enough time for existing dietary antigens to clear and the immune response to settle. Shorter trials frequently give false-negative results.

My dog has been eating the same food for years - can they suddenly develop an allergy to it? Yes. Food allergies develop through repeated exposure over time. A dog can eat chicken-based food for three years and then develop an allergy to chicken. This is why previously tolerated foods are not safe to use in an elimination trial.

Can I home-cook for the elimination diet? Yes, but it must be strictly nutritionally balanced for a home-cooked diet to be safe over 8–12 weeks. Your vet can refer you to a veterinary nutritionist or use commercial software to formulate a balanced recipe. An unbalanced home-cooked diet for this duration risks nutritional deficiency.

Can I test for food allergies with a blood test? Commercial blood tests for food allergies in dogs have poor sensitivity and specificity - they produce many false positives and false negatives and are not recommended for diagnosing food allergy. An elimination diet is the only reliable diagnostic tool.

My dog has both skin allergies and food allergies - is that common? Yes. Many dogs have more than one allergy - concurrent atopic dermatitis and food allergy is well-documented. Managing both requires treating environmental allergens and identifying food triggers, which is why response to atopy treatment alone may be incomplete.