On the occasion of World Dog Day, we look at a common condition affecting our four-legged friends: food allergies and intolerances. Here is what it's good to know to treat and prevent these disorders.
Food allergies and intolerances in our four-legged friends appear to be increasingly widespread. Dogs and cats, in fact, often suffer from problems related to their daily diet, with a range of symptoms that go from dermatitis to frequent vomiting and diarrhoea. In this field, however, a fundamental premise is necessary: foods are often wrongly blamed as the cause of common dermatological or gastrointestinal complaints without any real basis of intolerance or allergy, and this leads not only to an incorrect diagnosis, but above all to poor nutritional management.
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The support of a veterinary nutritionist is essential in cases of suspected food allergies or intolerances in dogs and cats, not only for diagnostic purposes, but above all to define a diet that takes into account the health status and therefore the nutritional requirements of the individual for whom it is designed. "Dogs and cats affected by adverse food reactions deserve an approach that goes beyond the elimination diet, which should have a defined duration and then allow for the gradual introduction of new foods," explains Dr Barbara Tonini, veterinary nutritionist. Allergies and intolerances to certain foods are not, in fact, expressions of the same disease. Both are, however, adverse food reactions that result in a variety of clinical presentations following the ingestion of a food (or, more rarely, an additive), either involving the immune system (true allergy) or without its involvement (in which case one speaks of food intolerance).
"Adverse food reactions with an immune basis are true food allergies and consist of an abnormal response by the immune system when a food that should normally be tolerated is ingested," explains Dr Tonini. "Food intolerances, by contrast, are adverse food reactions in which the immune system is not involved, but rather metabolic reactions (for example, failure to digest lactose or starch), pharmacological reactions (histamine from fish) or toxicological reactions (as occurs with garlic, onion, pathogenic bacteria or irritant substances)."
The onset of the first symptoms of these disorders can occur at any age (from 4 months to 12 years) in both dogs and cats. It has been calculated that in dogs 30 per cent of individuals show the first symptoms before the age of one, while in cats 50 per cent do so within two years.
Another interesting aspect is that these individuals, theoretically "allergic", often do not show the symptoms of allergies or intolerances again when they consume the "incriminated" food once more. The nutritionist explains: "This suggests that in some cases, underlying inflammatory bowel disease, there is a transient loss of so-called oral tolerance, and that therefore these are not true food allergies or intolerances in the strict sense, but it is more accurate to define them as diet-'responsive' enteropathies."
The foods most commonly responsible for food allergy and intolerance are proteins of animal origin. Among the most implicated meats are chicken and beef, as well as fish (especially in cats), milk and eggs. "Other protein sources to be considered with extreme care are plant proteins: wheat, maize, soya and rice are the most common," the expert continues. "Given that the foods listed above are among the most widespread, it immediately becomes clear that the choice for resolving symptoms should fall on a product with a single and novel (not previously consumed) animal or plant protein source (for example pork and tapioca)." Changing the brand or flavour of food without having assessed all the ingredients present in the diet makes no sense and does not resolve the situation.
Caution is also needed with certain ingredients that have a reputation for causing allergies or intolerances in our animal friends. "Gluten intolerance, and therefore coeliac disease, for example, plays only a marginal role in adverse food reactions in both dogs and cats (in the latter it has never actually been diagnosed)," explains Dr Tonini. "The common tendency to believe that gluten-free diets are healthier therefore has no real scientific basis, but is above all a trend, whose most fervent supporters are found among certain pet food manufacturers. Choosing to exclude wheat (or other cereals) from the diet can therefore only make sense within the context of an elimination diet, one that excludes this food because it was previously consumed."
"Among the most effective diets is the home-cooked one, which makes it possible to select foods without the interference of other ingredients (for example oil, protein sources, palatability enhancers) or additives (examples include antioxidants or thickeners) normally present in pet food," notes Barbara Tonini. If one chooses to go down this route, however, it is important to consult a veterinary nutritionist, rather than resorting to a do-it-yourself approach.
At present there are no truly reliable blood tests for the diagnosis of food allergy or intolerance. Numerous studies have, in fact, demonstrated that it is normal to find IgE or IgG antibodies against commonly ingested foods without any correlation with signs and/or symptoms of adverse food reactions being identifiable. "The level of these antibodies is correlated with the regular ingestion of the corresponding foods," observes Barbara Tonini. "50 per cent of dogs showed symptoms again after consuming one of the foods to which they had tested negative! Another widely used test, and one that is absolutely unreliable from a diagnostic standpoint, is the cytotoxicity test. This test, when repeated at different times, produces conflicting results in the same patient, with a high number of false negatives and positives that undermine its diagnostic reliability."
There are, however, certain breeds that are more prone to food intolerances and allergies in both dogs and cats. Among dogs we find the boxer, the dachshund, the poodle, the cairn terrier, the cocker, the collie, the dalmatian, the golden retriever, the labrador, the German shepherd, the English setter, and the Irish setter. Among cats, Siamese are among the most predisposed breeds. In any case, food allergies and intolerances appear to be increasingly widespread among our four-legged friends, even if the causes of this increase have yet to be clarified. The most widely accepted hypotheses are the same as those emerging in human medicine, pointing to the environment and our diet as the main suspects, though we must not forget the genetic aspect (and therefore an increase in the number of individuals belonging to predisposed breeds).