Adverse food reactions (Proceedings)
Adverse reactions to food are quite common in both dogs and cats. However, contrary to common believe, only few cases of adverse food reactions are due to true food allergies. Adverse food reactions represent a group of disorders that are defined by gastrointestinal, dermatological, and less commonly respiratory signs in response to ingestion of a certain food. It should be remembered that there are other specific conditions that are either thought to be due to or worsened by diet that are not considered adverse food reactions such as acute pancreatitis, megaesophagus, or portosystemic shunts.
A nomenclature of adverse food reactions has not been agreed upon for veterinary gastroenterology. The following definitions are therefore based on a nomenclature put forth by the American Academy of Allergy and Immunology. In general there are three groups of adverse food reactions: dietary indiscretion, non-immunologic adverse food reactions, and immunologic food reactions.
The most common type of an adverse reaction to food in dogs is dietary indiscretion. Dietary indiscretion is defined as an adverse reaction resulting from such behaviors as gluttony, pica, or ingestion of indigestible materials. Such behavior is commonly seen in puppies and the link between the ingestion of an "indigestible material" such as a ball directly leads to clinical signs such as vomiting, obviously without any involvement of the immune system.Non-immunologic food reactions or food intolerance includes several types of adverse food reactions such as metabolic food reactions, pharmacologic food reactions, food idiosyncrasies, and food poisoning. Metabolic reactions to food are defined as adverse reactions as a result of an effect of an unusual food component on the physiological metabolism of the animal or as a result of a common dietary component on the defective metabolism of the animal. The former is rather rare in dogs and cats but the latter does occur. The most common example is lactose intolerance, which is present in many adult dogs and cats. This condition is due to lack of the brush border enzyme lactase. Lactose can no longer be digested and will instead be fermented by members of the gastrointestinal microbiota, leading to clinical signs such as bloating, flatulence, and diarrhea. Pharmacologic reactions to food are reactions that are due to a pharmacologic effect in the host. One example of such a reaction is chocolate toxicity in dogs. In these cases the theobromine in the chocolate leads to neurologic, gastrointestinal, and renal malfunction and resulting clinical signs. Food idiosyncrasies are abnormal responses to a food substance or additive that resemble a hypersensitivity response but do not involve an immunologic mechanism. Food idiosyncrasies have been described in human beings but have not been well documented in dogs or cats. Food poisoning is an adverse reaction based on a direct toxic effect of a food. Food poisoning is usually due to toxic substances that have been produced by a microbial contaminant, but can also be due to a toxic principle naturally present in the food. One such example would be onion toxicity in dogs. Finally, food poisoning could also be caused by a toxic substance that has reached a pet food accidentally or through malicious behavior. Such an example would be the melamine scandal a few years ago where rice and wheat gluten from China had been found to have been adulterated with melamine, probably to falsely increase the protein content of said rice or wheat gluten.
Immunologic food reactions include food allergy and food anaphylaxis. Food anaphylaxis should be viewed as a type of food allergy that leads to systemic clinical signs.