Are Cats Lactose Intolerant? The Reason Why Milk & Kitties Don't Mix

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Reading picture books as a child may have taught you cats love nothing more than to lap up a bowl of milk. And while some cats may delight in the treat, it turns out milk isn’t a great source of nutrition for felines. Cats are lactose intolerant. Their bodies cannot properly process what they take in from milk products. Learn more about how it might affect your pet before setting down a bowl of milk.

Can Cats Drink Milk?

Like many of us, Cailin Heinze, VMD, MS, DACVN and Board Certified Veterinary Nutritionist remembers feeding the family cat milk when she was younger. “My dad let my cat lick the milk out of his cereal bowl every day for 15 years when I was growing up,” she says.

But just because cats do drink dairy, Heinze says doesn’t mean they should drink it. Cats are actually lactose intolerant—meaning their systems are not able to process the lactose found in milk properly, which results in digestive upset. In fact, Heinze notes lactose intolerance is pretty much the rule for all adult mammals (including humans).

How Does Lactose Intolerance Affect Cats?

“The most common signs of lactose intolerance are GI upset, such as diarrhea or vomiting,” Heinze says, noting some cats may not present these symptoms. She adds it’s also possible for pet owners to be unaware of these signs of intolerance, especially if you have a cat who spends time outdoors where their bathroom habits are not monitored, unlike cats who use the litter box each time they go.

Heinze explains why lactose has such an unpleasant effect on cats’ digestive systems (and humans, for that matter). “Lactose is a sugar, and undigested sugars draw water into the intestine, causing diarrhea,” Heinze says. “They are also fermented in the gut, and can cause bloating and flatulence.” So while your cat may like to drink milk, the after effects may be undesirable for both you and your kitty.

My Cat Drinks Milk and She’s Never Been Sick! What Gives?

Even if your cat has milk and does not get sick—like humans, some cats are able to handle milk better than others—there are actually no nutritional benefits to giving cats milk. While they drink their mother’s milk as a kitten, cats lose the ability to process lactose once they are weaned. While some studies have shown it may be easier for cats to digest cheese and other dairy products, experts like Heinze remind pet owners just because your feline likes a particular food doesn’t mean you need to offer it to them.

“If you feel strongly that you are going to feed your cat milk regularly, then you need to consider how many calories that is contributing to their diet so you aren’t contributing to [weight gain],” says Heinze, noting that obesity is the largest health concern for felines. “And you need to remember that milk is not nutritionally complete for cats.”

What Kind of Treats Are Safe to Give My Cat Instead of Milk?

Your cat’s dietary needs are pretty simple. She needs to drink fresh, clean water daily, and eat nutritionally-appropriate cat food that contains animal proteins (since cats are obligate carnivores—meaning their diet must contain meat). If you are going to give your cat milk, consider it a treat, and start with a very small amount to test for reactions.

Heinze says a good rule of thumb when it comes to giving your cat treats—including milk—is no more than 10 percent of their total daily calories. That generally means no more than 20 to 30 calories per day. A cup of skim milk contains 83 calories, while whole milk increases to 149 calories per cup. So really, a little goes a long way.

As for bottle-fed kittens who are still in need of mother’s milk, look for a kitten milk replacement formula product specifically made for kittens instead of standard cow’s milk. As far as other milk products marketed for cats in the pet food aisle, pay close attention to the calories they are adding to your cat’s diet. Have a conversation with your veterinarian or seek out the help of a board certified veterinary nutritionist to come up with a plan to help your cat maintain a healthy diet.