2. DairyThis almost surprises most people but dairy is not good for your cat. Many cats get an upset stomach from milk and diarrhea is common too. Who would have thought that cats would be inclined to have lactose intolerance? Turns out cartoons don’t always get it right. Your cat doesn’t actually know what’s best for it just because it might know to turn down spoiled meat. Milk is a contributing factor to feline obesity. Just like humans, the older a cat gets, the harder it is for them to process lactose. If a kitten was separated from their mother, the pet store sells special cat milk replacers, cows milk does not have the proper balance of whey and caseins. While kittens have the lactase they need to break down their mother’s milk, they don’t have it as they mature.