Elimination Diet Trials at Home: How Long, and What Counts
An elimination diet is the way to diagnose food allergy in dogs. What the reviews say about how long it takes, what to test first, and why labels mislead.
Written by thecanineledger
This page carries no advertising, and nothing on it is for sale.
A 2015 review found that “by 5 weeks in dogs and 6 weeks in cats after starting an elimination diet, more than 80 % of patients had achieved a remission of clinical signs” of food allergy (Olivry et al., BMC Veterinary Research 2015).
While five weeks is enough for most dogs, it isn’t enough for all. And the trial has a second half that owners often skip. This page sets out what the reviews say about each step, so you can plan the trial with your vet.
Our note: This page describes the trial, not how to choose the diet. A home-cooked diet can be unbalanced over eight weeks, so plan it with your vet.
1. How long the diet lasts
Eight weeks for most. “Increasing the diet trial duration to 8 weeks leads to a complete remission in more than 90 % of dogs and cats” with food allergy.
The review’s conclusion. “For diagnosing CAFRs in more than 90 % of dogs and cats, elimination diet trials should last at least 8 weeks.” CAFR stands for cutaneous adverse food reaction: a food reaction that shows in the skin.
A few take longer. “Fewer than 5 % of dogs needed an elimination diet of up to 13 weeks for a complete remission of signs”.
What it doesn’t show. The review pooled published case reports and studies, not a single trial.
Disclosure. The authors of all four reviews on this page have lectured for, and received research funding or fees from, a large pet food maker. The company paid the publication charges.
→ The Itchy Dog: Allergies, Atopic Dermatitis, and What Actually Helps
2. The challenge: putting the old food back
Why it matters. Getting better on the diet doesn’t prove food allergy. The diagnosis comes from feeding the old food again and watching for a flare. This is called a food challenge.
How long to wait. A 2020 review found the time for half of dogs to flare was 5 days, and for 90% it was 14 days. Its conclusion: clinicians “need to wait for 14 and 7 days for more than 90% of dogs and cats with a skin-manifesting FA to have a flare of clinical signs, respectively.” (Olivry and Mueller, BMC Veterinary Research 2020). FA is food allergy.
Fast flares. “About 9% of dogs and 27% of cats exhibited a flare of clinical signs on the first day after an OFC”. OFC is an oral food challenge.
Our note: Plan the challenge with your vet.
3. What to test first
The common culprits. A 2016 review found that “The most frequently reported food allergens involved in CAFRs in dogs were beef (102 dogs, 34 %), dairy products (51 dogs, 17 %), chicken (45 dogs, 15 %), wheat (38 dogs, 13 %) and lamb (14, 5 %).” (Mueller et al., BMC Veterinary Research 2016).
Where to start. Its authors say challenges “should begin with beef and dairy products”.
What it doesn’t show. The figures come from dogs in Australia, Europe and North America. They’re counts from published cases, not a survey of all dogs.
4. Why the bag may not be enough
Labels and contents. A 2018 review of pet food testing found ingredients not on the label in “0 to 83% (median: 45%) of tested diets”. For foods sold for elimination diets, the share was between 33% and 83% (Olivry and Mueller, BMC Veterinary Research 2018).
The conclusion. “The mislabeling of pet foods appears rather common, even in those with “novel” or “limited” ingredients proposed for elimination diets.”
Treats count. Anything else the dog eats during the trial can spoil the result. That includes chews and flavoured medicines.
Our note: The “treats count” point is ours, not from these reviews.
Our note: Ask your vet about flavoured medicines during the trial. Don’t stop them on your own.
→ Food Allergy or Environmental? Why Blood, Saliva and Hair Tests Don’t Tell You
5. What we could not verify
| Commonly said | What we found |
|---|---|
| “Two or three weeks is enough” | No. More than 80% improve by five weeks, and more than 90% by eight. |
| “If the itch goes away, it’s food allergy” | Not proven until a food challenge brings it back. |
| “A limited-ingredient food from the shop will do” | Risky. Between 33% and 83% of such foods contained unlisted ingredients, across the studies reviewed. |
| “Grain is the usual allergen” | Not usually. Beef, dairy and chicken were reported more often than wheat. |
Sources
- Olivry T, Mueller RS, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res 2015: systematic review. Authors funded by, and page charges paid by, a pet food maker
- Mueller RS, Olivry T, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res 2016: systematic review. Same disclosure
- Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labeling in commercial pet foods. BMC Vet Res 2018: systematic review. Same disclosure
- Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (9): time to flare of cutaneous signs after a dietary challenge in dogs and cats with food allergies. BMC Vet Res 2020: systematic review. Same disclosure
Always confirm with your vet before acting on anything on this page.