A diet trial is a way of diagnosing a food allergy or intolerance. The most common signs that you might see of a food allergy or intolerance are:
- skin problems (e.g. itching, baldness, redness of the skin)
- digestive system problems (e.g. vomiting and diarrhoea)
There is no short-cut to diagnosing food allergies. Blood tests and hair samples are not accurate and are a waste of money.
A diet trial involves giving a specific food, excluding everything else (i.e. treats, flavoured supplements) apart from plain water. It should be carried out for at least 4 weeks, up to 8 weeks if no improvement seen after 4 weeks. If there is no improvement in the symptoms at this point, a food allergy or intolerance can be excluded. If there is an improvement, to make a proper diagnosis, the original food should be re-introduced to see if the problem recurs. If it does, that is a clear diagnosis of food allergy or intolerance.
What food should I use?
Using a food which is simply sold as ‘hypoallergenic’ is not suitable. The term is not regulated in any way and animals can still have allergies and intolerances to the ingredients.
Commercial hydrolysed diet
This is the option most commonly recommended. These diets are specially formulated for diet trials. The protein component of the diet goes through a special process called hydrolysis which cuts the protein up into small portions which are too small for the body to react to. There are several different products available but they cannot be found in a normal pet shop. The best option is usually to choose one which is made from a soy or chicken feather protein, rather than meat, as it is still possible for a particularly sensitive pet to react to a meat-based one. These foods are still complete diets so provide all the nutrients and minerals that your pet needs and can be used on a long-term basis if needed.
Home-cooked novel protein diet
These are okay for a short-term diet trial but will not be balanced so in the long-term can cause deficiencies of vital nutrients. It is important to choose a protein source which your pet has never had access to in the past. Some suggestions include:
- wild boar
This should be combined with a novel carbohydrate source such as potato or oats.
How do I do the diet trial?
The new diet should be introduced over a period of a week, gradually reducing the old food and increasing the new. Thoroughly clean bowls, scoops and food storage bins to remove any trace of the old food.
After a week, your pet should be only on the new diet. They should have this to eat and plain water to drink.
While your pet is on the diet trial DO NOT GIVE:
- chews such as rawhide or pigs ears
- flavoured medication (unless checked with your vet)
- flavoured toothpaste
- flavoured chew toys
- any other food to give medication
If you want to give your pet a treat, you can give them some of the special food, or use some of the hydrolysed canned food baked in the oven.
Make sure that your pet does not have access to any food belonging to other pets or any ‘human food’. Keep your dog on the lead when outside and prevent scavenging. If you have a cat, it is best to keep them indoors for the duration of the diet trial to prevent hunting or stealing food from elsewhere.
If you have multiple pets, microchip-controlled bowls are a great way to ensure that each animal eats the right food.
What do I do after the diet trial?
The next step depends on whether there has been an improvement or not.
My pet has not improved
Where there is no improvement, as long as the diet trial has been carried out properly, a food allergy can be ruled out. You vet may wish to carry out further investigation to determine the cause of the problem in the case of gastrointestinal problems, or in skin problems, an environmental allergy is more likely and your vet will advise you on treatment options for this.
My pet has improved
To make a firm diagnosis of a food allergy, the pet should be given the original diet again to see if the problem comes back. Many people are reluctant to do this, however.
An alternative is to gradually add in different ingredients, one every 2 weeks, to try to determine what your pet can cope with, or what they can’t. A complete diet can then be looked for which contains only these ingredients. Feeding a home-cooked diet is not recommended on a long-term basis as this will cause nutritional deficiencies.
It is possible to feed a complete hydrolysed diet on a long-term basis without any problems, although they are quite expensive.