Food allergies and intolerances: the elimination diet explained

A true food allergy arises when the immune system recognises as an enemy a food protein it has already met many times. That is why it almost always develops towards a familiar ingredient, not a new one: repeated exposure is needed for the reaction to build. An intolerance is a different, digestive matter, and can depend on a poorly tolerated fat, an additive or the quantity. Alongside these two, and far more common, are the causes with no link to food: parasites, flea bite allergy, environmental allergies to mites or pollen, and skin and ear infections.

Working out which group you are in changes everything, because a strictly run elimination diet is of little use if the problem was a flea or a mite. That is why the first step is not the bowl but the consultation: the vet rules out the most common causes before starting a path that lasts weeks.

The logic is simple: if you remove the protein that triggers the reaction and the signs improve, and they return when that protein is reintroduced, the link to food is proven. To work, the diet must contain a protein source the animal has never eaten, or a hydrolysed protein, that is one broken into fragments too small for the immune system to recognise. The vet chooses between the two based on the animal's food history, which has to be reconstructed honestly: even a daily treat is food.

The critical point is not which diet you choose but how strictly you follow it. A single different mouthful is enough to void the trial and waste the weeks spent. That is why the hardest part of an elimination diet is not nutritional but organisational: it involves the whole household and everything the animal can get into its mouth.

1. 1

   Reconstruct the food history with the vet

   List every food, treat, supplement and scrap given over recent months. It helps choose a genuinely new protein or favour a hydrolysed one.

2. 2

   Feed one diet and nothing else

   During the trial, the chosen diet is the only thing that goes into the bowl. No different treats, no scraps, no flavoured snacks, no edible chews.

3. 3

   Watch flavoured medicines and toothpastes

   Some parasite tablets and chewable products contain meat flavourings. Ask the vet for neutral alternatives for the trial period.

4. 4

   Continue for the full time without stopping

   It usually takes several weeks before you can judge, because skin and gut heal slowly. The vet sets the exact duration.

5. 5

   Record signs with a steady measure

   A daily itch score and a note on the stools make a gradual improvement visible that the eye, day by day, misses.

6. 6

   Rechallenge only with the vet

   If signs improve, the old food is reintroduced to confirm it is the cause. This is the step that turns a suspicion into a diagnosis.

Most elimination diets do not fail because the diet was wrong, but because it was not respected. Knowing the common traps in advance is the best way to avoid running a long trial twice.

• Changing food after a few days because no result shows: skin takes weeks to respond, not days.
• Still giving the usual treat, convinced a small amount does not count: to the immune system it counts.
• Forgetting access to other food: another pet's bowl, dropped kibble, food scavenged on walks.
• Choosing a supermarket single protein food alone: many contain traces of other proteins not clearly declared.
• Stopping as soon as signs improve without a rechallenge, and so ending up without a real diagnosis.
• Applying the strict rule to only one of several pets, letting them swap bowls.

Once the culprit protein is identified, management becomes simple in principle and careful in practice: that ingredient is avoided for good. This means reading labels with the same care described for any complete food, because the same protein can hide under different names or appear as a minor ingredient.

An animal with a confirmed food allergy can still, over the years, develop sensitivity to other proteins, and can have environmental allergies in parallel that food does not explain. So management is not a single event but a dialogue that continues with the vet, especially if itching returns after a period of wellbeing. Recording episodes over time helps tell a new sensitivity from a seasonal flare or a slipped dietary lapse.

1. Keep a written list of banned ingredients and share it with anyone caring for the animal in your absence.
2. Choose treats that respect the same restriction, or use part of the ration as a reward.
3. Reread the label at every repurchase, because formulations change without notice.
4. Report any return of itching to the vet, with the date and what was given in the preceding days.