1. Onions and garlic
Onions contain a substance (N-propyl disulphide, for you scientists out there) that can destroy the red blood cells in cats, causing a condition called Heinz body anemia. Symptoms include lethargy, loss of appetite, weight loss, and rapid breathing/pulse. Garlic also contains this substance, though to a lesser extent. Shallots, leeks, and other related vegetables are also off-limits. Pay special attention to this one–several foods commonly fed to cats (baby food, meat gravy, etc.) contain onion and can lead to Heinz body anemia over time!!!
2. Nightshade vegetables
Tomatoes (especially green ones), potatoes, eggplants, and other nightshade vegetables will cause severe gastro-intestinal distress for your cat due to a substance called Glycoalkaloid Solanine. And as anybody who’s had to clean up a messy litterbox or experienced a cat fart knows, that’s bad news! Cooking can neutralize the substance, but why bother when your cat is a carnivore and can’t really digest vegetables anyways?
3. Chocolate
We all know about how toxic chocolate is for dogs–but it’s also bad for cats! Neither species can digest theobromine, a substance found in the cacao bean. If you really must feed your cat chocolate, please stick to white chocolate, as it contains insignificant amounts of the substance. Or better yet, don’t feed your cat any chocolate at all.
4. Milk
Forget that age-old image of Mittens lapping from a bowl of milk–the truth is that milk is harmful to cats and can cause digestive distress. Cats, like lactose intolerant humans, do not have sufficient amounts of the enzyme lactase to efficiently digest milk. It may not cause death, but it can case diarrhea, gas, and vomiting. If your cat is currently a milk-addict, then try switching to lactose-fee milk or heavy cream (feed 1/4 cup or less at a time), which has less lactose than regular milk. Your best bet is, of course, to get him off milk completely.
5. Grapes and Raisins
It is well-documented that grapes can cause diarrhea and renal failure in dogs, and the ASPCA recommends not feeding them to your cat either. Nobody is quite sure why grapes are so dangerous, but better safe than sorry!
If your cat has ingested any of these foods, please get him to the vet right away!