Adverse Reactions to Food in Cats

I’m not sure I understand the difference between food allergies and adverse reactions to food in cats. My veterinarian tells me that food allergies—like shellfish allergies in humans—are actually not as common in cats as one might think. Is there really a difference?

food_aversion_in_catsTraditionally, the terms “food allergy” and “food intolerance” have been used to describe any and all adverse food reactions in cats. The term “food allergy” or “sensitivity” is really most accurately applied when the immune system is involved in creating the signs and symptoms that result. “Food intolerance” is a far more accurate term to describe adverse food reactions in cats that cover a large category of reactions that do not involve the immune system and are generally digestive issues.

Adverse food reactions in cats often mimic food allergies because there are only so many ways that the body can demonstrate a problem with food. One characteristic of food intolerance is that it occurs on the initial exposure to that food or food additive. Immune-system regulated reactions (allergies or sensitivities) generally require several exposures before signs are seen. The incidence of food intolerance versus food allergy is not known. There are several general categories of food reactions that may occur in cats:

Food poisoning

Food poisoning is an adverse reaction caused by the direct action of a food on the cat. Food poisoning may include the following:

  • Ingestion of excessive amounts of a specific nutrient like vitamin A or vitamin D
  • Scavenging of putrefied food
  • Ingestion of plants that can cause GI irritation like rhubarb

Food additives

Adverse reactions to food additives are frequently reported in people and include compounds like sulfites, monosodium glutamate, and certain spices. Despite an impression that food additives can cause problems in cats, data are lacking. One food additive that can cause problems is disulfide. Disulfides are found in onions and can cause damage to red blood cells.

Drug-like reactions to food

Histamine, which can sometimes cause severe clinical reactions in humans—flushing, diarrhea, sweating, nausea, vomiting, and facial swelling—may not be an issue in cats except for the occasional idiosyncratic reaction.


There are several important disorders of carbohydrate intolerance in humans. Recognized carbohydrate intolerance in cats is less frequent. One fairly common carbohydrate reaction in cats is lactose intolerance. The signs include diarrhea, vomiting, bloating, and abdominal discomfort after ingesting cow’s or goat’s milk.

Dietary indiscretion

Dietary indiscretion is far more common in dogs than in cats, but cats are not immune to eating things they should not. Gastrointestinal signs may be caused by bacterial contamination, fat or grease, or from bones.

It is important to distinguish whether a cat’s reaction to something they have eaten involves an immune system reaction, or whether it is a gastrointestinal issue. Either type of reaction requires a comprehensive approach to restore the body to a state of balance. Knowing the cat’s feeding schedule, nutrient profile, and the timing and severity of any signs and symptoms will help your veterinarian distinguish between a one-time adverse food reaction and a food allergy or hypersensitivity


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