How to Do an Elimination Diet for Your Dog: Week-by-Week Guide

By BEANS Team · Published 2026-10-25

Most diet trials do not fail because the food was wrong. They fail because something else got in: one treat, one flavoured tablet, one lick of the other dog's bowl. Here is how an elimination diet works, week by week, and how to keep it clean from start to finish.

What is an elimination diet for dogs?

It is how your vet finds out whether food is behind your dog's itch. Your dog eats one diet, and only that diet, for at least eight weeks, then your vet brings old foods back one at a time to see what causes a flare.

Merck's Veterinary Manual calls dietary elimination trials "the reference standard" for diagnosing food allergy in dogs and cats. The diet is usually one of two kinds, and your vet will choose:

• Novel protein. VCA describes this as "one protein source and one carbohydrate source that your dog has never eaten before."
• Hydrolysed. A therapeutic diet in which the proteins are broken into pieces too small for the immune system to recognise, as VCA puts it. Tufts' Lisa Freeman notes most veterinary dermatologists recommend an extensively hydrolysed diet for skin disease.

Want to watch why diet trials fail in 64 seconds?

Our short film follows Miya through the eight weeks and the three slips that send most trials back to the start.

What do you need to do before week one?

See your vet first. VCA says your vet should examine your dog, "because there are many causes for these clinical signs." A food trial run on a dog with fleas or a skin infection gives you a muddy answer.

Before the trial starts, your vet may:

• Treat any infection. Merck says secondary infections with Staphylococcus or Malassezia (a yeast) are common in food-allergic dogs, and "it might be appropriate to treat the patient's secondary infections before beginning the elimination diet."
• Sort out flea and heartworm protection. Keep it going: Tufts says it is "very important" to continue preventatives during the trial. The catch is flavour. Merck notes chewable or flavoured flea and heartworm products "generally contain beef, pork, or soy protein" and recommends unflavoured, injectable or topical products instead.
• Choose the diet. What counts as novel depends on what your dog has already eaten, and Merck says it should be chosen with cross-reactivity in mind. Freeman recommends veterinary diets over shop-bought limited ingredient foods, citing "high rates of contamination with common proteins" in over-the-counter ones. A home-cooked diet must be balanced, ideally by a veterinary nutritionist, says VCA.

Then clear the house. Tufts suggests throwing away or giving away every commercial treat in the home, and warning dog walkers, guests and anyone else who might hand one over. A sign on the fridge helps everyone remember.

What does an elimination diet look like week by week?

Every trial is planned by your vet, but most follow the same shape. Tufts' plan counts the trial from the date you finish switching to the new diet, not the day you open the bag.

Do not stop early just because your dog looks better. The challenge at the end is what proves it was the food.

How long does an elimination diet take to work?

At least eight weeks. That figure comes from a 2015 review by Olivry, Mueller and Prélaud in BMC Veterinary Research, which pooled published reports and concluded that "elimination diet trials should last at least 8 weeks" to diagnose food allergy in more than 90% of dogs and cats.

For dogs, the numbers looked like this:

• By week 3, about half of dogs had a marked reduction in signs.
• From week 5, signs had returned to normal in more than 85%.
• With an eight-week trial, that rose to over 95%.

Now the careful version. The dog figures were pooled from 209 dogs across earlier studies, which is not a large number, and the authors themselves say there is "currently no consensus on the duration" of trials. Merck cites a literature review suggesting "a minimum of 10 weeks might be required to identify 95% of food-allergic patients", and Freeman says specialists generally recommend 8 to 12 weeks for skin problems. So eight weeks is the minimum, not a guarantee. Your vet may ask for longer.

Merck also notes a trial can sometimes be shortened to about four weeks if the diet is started alongside a short course of prednisolone. That is a vet decision for some dogs, not a shortcut to try at home.

What ruins an elimination diet?

Anything else that goes in your dog's mouth. Freeman puts it plainly: a successful trial "has to control everything that goes into your pet's mouth." VCA warns that if prohibited items are eaten, the trial is compromised "and you may need to start over."

The usual slips, from the Tufts checklist:

• Treats, including rawhides, pig ears, bully sticks and other dried animal parts
• Dental chews and flavoured chew toys
• Flavoured medications, such as chewable heartworm or flea and tick tablets
• Pill pockets or food used to hide tablets: ask your vet for another way
• Pet toothpaste: Tufts suggests brushing without it during the trial
• Supplements, unless your vet specifically recommends them. That includes our own supplement chews, which contain pork
• People food, even fruit, vegetables and anything containing gelatin, like marshmallows
• Dropped food: Tufts suggests keeping your dog out of the room when children eat

And the one that is easiest to miss: the other pet's bowl. Tufts says to "prevent access to the food of any other pets in the house." In a compact flat with a cat or a second dog, bowls are often a few steps apart. Feed them in separate rooms, pick bowls up as soon as meals end, and keep cat food somewhere your dog cannot reach.

If your dog does sneak something, tell your vet. They will decide whether to carry on or restart.

How do you track your dog's itch?

Score it once a week from 0 to 10 and write it down. Vets use owner-scored itch scales like this, and memory is unreliable over eight weeks.

The best-known one was developed by Hill, Lau and Rybnicek (2007) and tested further by Rybnicek and colleagues (2009) in Veterinary Dermatology. The 2009 study set a normal range of 0 to 1.9 for dogs without skin disease. Ask your vet which scale they want you to use.

Alongside the score, note:

• Where your dog scratches, licks or chews
• Any ear trouble, loose stools or vomiting
• Every slip, with the date
• Any new medication

What happens after the elimination diet?

If the itch improves, your vet will challenge with old foods one at a time. Merck says food allergy "is not considered to be confirmed" unless the dog improves on the diet and then relapses when the old food comes back.

How quickly does the itch return? VCA says signs "typically appear in one to three days but can take up to four weeks." Merck says positive challenge responses can take up to 10 to 14 days to appear, so it advises bringing back individual foods no more often than every two weeks. If your dog flares, Merck says they go back on the elimination diet.

The result is a list of foods your dog can and cannot eat. If the itch never improved on the diet, food probably is not the main cause, and your vet will look at other possibilities, such as environmental allergy. Our guide to where your dog scratches explains how the patterns differ.

Can my dog have treats during an elimination diet?

Only what your vet approves. The Tufts plan has a line for "Recommended treats" with a box for "Recommend no treats during trial", which says it all: the vet decides.

Kangaroo Freeze-Dried Pet Treats (SGD $19.90): Pure kangaroo. Nothing else. A novel protein for itchy, sensitive dogs and high-value training.

BEANS Kangaroo treats are a single ingredient, 100% kangaroo, with nothing else added. If your vet has chosen kangaroo as your dog's trial protein, ask whether a treat like this fits the plan. If the trial protein is anything else, or your dog has eaten kangaroo before, it is not suitable. Never add a protein to a trial on your own.

If you are still exploring options, our guide to novel proteins in Singapore covers what is available, and you can browse the itchy pets collection.

Why not just do a food allergy test?

Because the blood, saliva and hair tests sold for food allergy are not reliable. Merck says "none of these methods reliably give consistently accurate results." VCA says the same of tests that claim to find food allergies through blood, saliva or hair.

A Tufts Petfoodology summary by Cailin Heinze describes two 2019 studies. In one, healthy dogs and food-allergic dogs tested positive at similar rates. In the other, 60 to 100% of 30 healthy dogs tested positive for one or more foods. Her conclusion: these tests "should not be used for diagnosis of food allergy." For more on how food allergy causes itch, read Food Allergy in Dogs: How It Causes Itch and How Vets Test It.

Bottom line

An elimination diet is simple on paper: one diet, nothing else, at least eight weeks, then a challenge one food at a time. Most trials fail on the extras. Plan it with your vet, score the itch weekly, and guard every bowl in the house.

Starting a trial this week? Book your vet visit, and ask about the trial protein before you buy a single treat.

This article is general information, not veterinary advice. If your pet has ongoing symptoms, see your vet.