Many of the same foods that pose a health risk for dogs are also dangerous for cats. Why then is the topic of feeding human foods to cats so rarely discussed?

My guess is that owners simply assume that a cat’s discriminating palate will prevent any problems from developing. Sometimes this proves to be the case, but in other instances, cats have eaten enough of a "forbidden food" to become ill. Following are the top three types of human foods that I tell clients never to feed their cats.

1. Onions, Garlic, Leeks, and Chives

The members of the genus Allium contain organic sulfur compounds that cause oxidative damage to feline red blood cells. The oxygen carrying molecule hemoglobin is so altered by this chemical process that it clumps together and forms a structure called a Heinz body that is visible within red blood cells under the microscope. These damaged cells die more rapidly than normal, resulting in a potentially life-threatening anemia.

Cats that eat as little as 2.3 grams of onion per pound of body weight can become sick, usually within a few days of exposure. Allium spp. are ingredients in many products (e.g., baby food), so owners should carefully examine labels before offering anything new to their cats.

Symptoms of Allium poisoning include depression, a yellowing of the skin and mucous membranes, abnormally dark urine, rapid and/or deep breathing, weakness, exercise intolerance, and cold sensitivity. Loss of appetite, abdominal pain, and diarrhea may also develop. Treatment can involve inducing vomiting (if the cat has recently eaten the problematic food), administering activated charcoal to prevent absorption of the toxins, supportive care, oxygen therapy, and blood transfusions.

2. Grapes and Raisins

We don’t yet know what the causative agent is, but eating grapes or raisins can lead to kidney failure in cats. Vomiting, diarrhea, lethargy, and increased thirst and urination are the first symptoms that develop; but as the kidneys continue to shut down, urine production may slow and then stop altogether.

Inducing vomiting and giving activated charcoal can help in cases that are caught early. Kidney failure is typically treated with aggressive intravenous fluid therapy or other forms of diuresis and symptomatic care (e.g., anti-nausea medications). Prognosis depends on the extent of the damage done to the cat’s kidneys.

3. Chocolate

Chocolate contains compounds called methylxanthines (specifically caffeine and theobromine) that are potentially dangerous for cats. In general, the darker the chocolate the more methylxanthines it contains. For example, unsweetened baker’s chocolate contains up to 500 mg of methylxanthines per ounce, while dark semisweet chocolate is in the 155 mg/ounce range, and milk chocolate contains up to 66 mg/ounce.

At low levels, chocolate intoxication causes vomiting, diarrhea, and hyperexcitability. Higher doses can result in nervous system dysfunction (e.g., seizures), irregular heart rhythms, and death. Mild clinical signs of chocolate poisoning are seen when a cat ingests around 9 mg per pound of body weight. More severe problems occur when cats get into 18 mg or more of methylxanthines per pound body weight.

Inducing vomiting and/or giving activated charcoal to the cat are options when treatment can be initiated within a few hours of ingesting a potentially dangerous amount of chocolate. Otherwise, therapy is limited to intravenous fluids and symptomatic care (e.g., for seizures and cardiac arrhythmias) until the body can rid itself of the toxins.

Dr. Jennifer Coates

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