If your cat experiences severe or repeated vomiting or diarrhea after meals, your veterinarian should be contacted. Unaddressed and undiagnosed eating problems can lead to more serious health issues, so medical treatment is important. Once under your vet's care, more detective work is necessary. The first order of business will be to determine if your cat's food intolerance is being caused by "food poisoning" or allergies.

Cat owners can sometimes find feeding their pets to be a challenging proposition. Felines are of course well known for their picky eating habits. But sometimes even when foods are found that are pleasing to the cat's palate, issues in the form of intestinal, skin, behavioral, and respiratory problems may occur. Adverse dietary reactions in cats are categorized in one of three ways- food intolerance, food intoxication, and food allergies.

Dietary reaction symptoms can be shared by other medical conditions including irritable bowel syndrome and cancer, another reason why early medical diagnoses is important. Symptoms include:

While dietary reactions in cats can be broken down into three distinct subsets, the symptoms in all three cases can often be identical, making determination of the specific cause difficult. Elimination and even observation of the cat's habits may be needed to make a correct diagnosis.

Cats have extremely sensitive dietary systems. Sudden changes to a cat's diet can certainly result in adverse dietary reactions, also known as food intolerance. This is why cat owners are cautioned to make any diet changes by introducing small amounts of new food over an extended period of time. In addition to a dietary reaction being caused by a new type of food, intolerance can also be caused by indirect methods. These dietary reactions can be stimulated by: 

Ironically, the various elements that may be causing adverse dietary reactions in cats may be there because of humans. The coloring, appearance, and odor of pet food is often there to make it more appealing to the humans that serve it, without it doing much for the animal. Pet owners should make sure that veterinarians are aware of any "upgraded" or "new and improved" food that their cat is eating, even if it's the same brand that the animal has been eating for some time. 

In addition, as with humans, chemicals are increasingly producing dietary reactions in cats. Persistent halogenated hydrocarbons (PHAs) are a type of chemical that can now be found in exterior and interior environments, both directly in foodstuffs and in their wrappings and containers (largely certain types of plastic) that can also leach into food. 

The dietary reaction known as food intoxication is often also referred to as "garbage poisoning", because it generally occurs after the pet has consumed household food waste. Unlike food intolerance, food intoxication can result in GI tract bacteria motility being adversely affected by "bad" bacteria. In a best-case scenario, the cat corrects the situation with vomiting and/or voiding of its bowels, and is much improved within a few hours. But severe cases of food intoxication produce a neurological condition, called Penitrem-A toxicity, which is much like strychnine poisoning. Penitrem-A toxicity symptoms include: 

Botulism is another serious by-product of food intoxication, and symptoms here include:

If a cat experiences more than several hours of vomiting and loose stool, owners should not wait for any of these additional symptoms to begin, but should seek emergency care immediately. 

Food allergies in cats are not caused by a direct reaction to the consumed food itself, but rather is an immune system reaction to it. Food allergy symptoms commonly include vomiting and loose stool, and often include skin and respiratory problems. There are no effective testing methods available for allergy testing in animals. Rather, if food poisoning has been eliminated as a cause of symptoms, the affected animal will be placed on a very limited diet to determine allergies. 

The vet will begin by asking the cat owner to recollect the appearance of symptoms and events (new foods, new feeding dishes, cat with access to spoiled food, etc.) To then determine if symptoms are being caused by food intolerance, the cat will be returned to its pre-symptom diet. If symptoms remain, allergies may be indicated, in which case the cat will be placed on a diet that it has no previous exposure to, commonly duck and peas. The cat will remain on this diet for an extended period while being monitored for symptoms. If true food poisoning or food intoxication is thought to be the cause of symptoms, than the vet will conduct urinary, fecal, and possibly blood tests. Owners can help in this diagnoses by noting all changes to that cat's routine, and in quickly taking the cat in for treatment if symptoms don't quickly subside.

If food intolerance is diagnosed as the cause for symptoms, the cat should avoid all food and treats that seemed to spark a dietary reaction. It should also consume food and water from ceramic and metal bowls. Treatment is generally out-patient. 

Allergies are treated by keeping the cat on a prescribed diet for several months while monitoring for symptoms. Because of the difficulty in diagnosing allergies, it's generally recommended that pets be kept on this new diet, with additional food types being added slowly and carefully. Treatment is generally out-patient. 

Severe food intoxication in cats is treated by "flushing" the system out. Mild cases of food intoxication can be treated with bland foods, such as cottage cheese. Severe cases require the digestion of charcoal. Cats with mild cases of food intoxication may be sent home, while severe cases will require hospitalization.

If owners keep cats suffering from food allergies on a limited diet, cats generally do quite well. It is possible to develop reactions to low-allergen foods over time, so owners should remain diligent for changes and symptoms. Likewise, with food intolerances, if the offending materials are quickly found and eliminated, cats generally make a full recovery. Owners should be careful to check all new food sources for offending ingredients, and be attentive to the presence of chemicals and plastics in feeding areas. In the case of food intoxication, a generally healthy cat receiving immediate treatment usually recovers fully. To avoid future incidents, owners should keep cats indoors at all times, and control the cat's access to spoiled food and other garbage.