Are Cats Lactose Intolerant? – Catmart
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Nutrition

Are Cats Lactose Intolerant?

Cats love milk—just like the cat who got the cream. But is feeding cats milk safe, is milk good for cats, or can they experience lactose intolerance like us?

Can cats have milk? Cats become lactose intolerant when they wean, i.e. when they stop drinking mother’s milk and start eating solid foods. That’s because its gut stops producing lactase, which is the same problem as is seen in lactose intolerant people. If the cat is continually fed cow’s milk by a person, however, it won’t become intolerant as its gut will still produce lactase. The signs of lactose intolerance in cats include gas, diarrhea and vomiting, but there are no long-term effects.

The guide below first defines lactose intolerance in cats, and how it’s similar/different to that seen in humans. It will also address how common lactose intolerance is in cats, and why is milk bad for cats even beyond intolerance.

What Is Lactose Intolerance?

Can cats drink milk?
Can cats drink milk? Weaned cats shouldn’t, but if you never wean them fully, they’ll be fine. Image courtesy of Pixabay.

Lactose intolerance is caused by lactose malabsorption. That means the gut struggles to break down and absorb lactose, a kind of sugar found in dairy products.

The reason for this problem is that a lactose intolerant cat’s gut doesn’t contain enough lactase (with a second a instead of an o). Lactase is an enzyme, enzymes being the tools that the gut uses to break down proteins, sugars and other things found in food.

What happens is that the lactose is normally broken down in the small intestine, but in this case, it passes through into the colon (large intestine) undigested. The bacteria in the colon then break the lactose down, which isn’t ideal, because this process produces lots of fluid and gas. This fluid and gas are what’s responsible for the symptoms of lactose intolerance.

Mammals & Milk

The root cause of lactose intolerance is that mammals aren’t supposed to continue drinking milk into adulthood.

Mammals are defined as a large group of animals with certain things in common: we all give birth to live young and feed it with milk. Cats do the exact same, as they nurse their young after they give birth to them. This milk contains high levels of fat and protein, which young mammals need to a) support their high energy lifestyles, and b) to grow. The milk of each mammal is perfectly formulated for its young, i.e. with the right levels of carbohydrates, fat and protein, and with the precise vitamins and minerals the young needs. The offspring’s gut contains the corresponding enzymes needed to break down these nutrients.

However, once the young reaches a certain age, it stops drinking milk. This is known as weaning, and it’s normally a slow process. The young will try solid food for a while, but continue drinking milk to support its development. Eventually, though, all mammals that reach adulthood stop drinking milk once and for all. Throughout the weaning process, your cat’s gut will stop producing the enzymes needed to break down milk (and lactose), and produce enzymes that can break down meat instead. Producing lactase when it doesn’t need to would be a waste of your cat’s time and resources.

Genetic vs. Natural Lactose Intolerance

There are two kinds of lactose intolerance in nature. There is the kind described above, wherein a mammal stops producing lactase once it becomes mature.

The second kind is genetic, and this is the kind that most people have. Genetic lactose intolerance is where the body doesn’t know how to produce lactase at all, even during the early stages of life. This means that dairy products cause the effects of lactose intolerance from the moment the kitten is born. In such cases, the kitten would fail to thrive without intervention, since it would be unable to feed on its mother’s milk. It’s typically the former kind of lactose intolerance that’s relevant to cats.

You may be wondering where this leaves cats and milk. Cats are famous for enjoying dairy products, especially milk and cream. But this ‘cats and milk myth’ isn’t based in reality.

Are All Cats Lactose Intolerant?

Not all cats are lactose intolerant. However, lactose intolerance is the norm while the ability to continue drinking milk is abnormal.

Through the weaning process described above, all housecats would become lactose intolerant without human intervention. But since giving cats milk is so popular, some cats never stop drinking milk from the early stages of their lives until they get old. These cats never stop producing lactase, and therefore never lose the ability to process lactose. These cats can therefore safely eat and drink dairy. It’s if there’s a gap between weaning and about 6 months that the cat will become intolerant of lactose.

What Percentage of Cats Are Lactose Intolerant?

There aren’t any stats on how many cats are lactose intolerant. It’s likely that most of them are, as feeding cats milk seemed to be more popular in the 20th century than in the 21st.

Furthermore, this isn’t a major issue either way. Cat foods are made without dairy in them, because even if cats weren’t lactose intolerant, they prefer a diet high in meat more than anything else.

At What Age Do Cats Become Lactose Intolerant?

Cats stop drinking milk at the age of weaning. Weaning begins about four weeks into a cat’s life, and should be completed between 8 and 10 weeks of age. The kitten will gradually drink less and less milk, and will eat more and more solid food.

Throughout this process, the cat’s gut will produce less and less lactase. It will retain the ability to produce it up until about 6 months of age. But if the cat stops drinking milk, it will lose the ability to produce any lactase, and so become fully lactose intolerant.

Why Do People Feed Cats Milk If They’re Lactose Intolerant?

my cat wont drink, cat water fountain, cat bowls
It’s all about what the person thinks, rather than what the cat thinks!

It seems to be an entirely cultural thing. People assumed that since cats enjoy drinking cream, it must be good for them. Over time, this view became entrenched in western culture (e.g. in the phrase ‘the cat that got the cream’). This cultural memory is passed down from generation to generation.

This is a particularly difficult perception to shift because many cats aren’t lactose intolerant. A person who has fed their cat cream from the time it was a kitten will have a cat that isn’t lactose intolerant. If they were ever challenged by somebody who thinks cats can’t eat dairy, they could rightly say that their cat has never had a problem. At the same time, the person who thinks cats shouldn’t eat dairy won’t feed dairy to their cat, and so it will be intolerant.

Why Do Cats Drink Milk If They’re Lactose Intolerant?

Cats seem to love high-fat dairy products like cream. But why would they eat them if they cause the symptoms of lactose intolerance?

The reason is to do with your cat’s evolutionary history. All animals struggle in the wild, both to find food and shelter. Even in areas of abundance, there is likely to be less food in winter. It’s for this reason that mammals have fat stores: wild cats can convert unused energy from excess food in summer into fat, and keep it for later use. That’s why animals enjoy high-fat, high-protein, high-calorie foods.

Let’s say that a wild cat comes across some kind of nutrient-dense food. Winter is approaching. Even if it isn’t hungry, it will eat whatever food it has found, because this could help it survive through the difficult winter. This fits in with what we know about the overall cat diet, too: according to the journal Veterinary Sciences, ‘studies show that domestic cats balance macronutrient intake by selecting low-carbohydrate foods.’

Unfortunately, your cat doesn’t know that it’s not living in the wild anymore. Or, at least, its body doesn’t. So, when it sees dense high-fat foods, it wants to eat or drink them. It’s for the same reason that we love snacks so much.

How Can I Tell If My Cat is Lactose Intolerant? (Symptoms)

If your cat is lactose intolerant, it will experience the same symptoms of lactose intolerance as a person. That’s because the mechanism by which cats can’t digest lactose is the same by which certain people can’t digest lactose (i.e. a lack of lactase). Since a cat’s gut is in most ways similar to ours, the same symptoms will result.

1) Gas

The first symptom you’re likely to notice is gas. This occurs when the undigested dairy travels through your cat’s small intestine and into its colon. It’s here that the gut bacteria start to break down the lactose, which should really be the job of lactase. Bacteria produce gas when they break down food.

This will be the first symptom to occur. That’s because it’s once the bacteria start to break down the lactose that the gut realizes there’s a problem. It will then do something about it, and that ‘something’ usually isn’t pretty.

2) Diarrhea

Your cat’s gut will take steps to get rid of the lactose in its colon. This is a preventative measure; if it didn’t, it would continue to create gas, which is painful for the cat. So, the gut essentially tries to shoot out the partially-digested food before it causes any more trouble. That’s what diarrhea is.

How soft the diarrhea is depends on how much dairy your cat ate. If it had hardly any, then your cat may only experience soft stools. If it ate a lot, then they may be wet. The wetness of the stool is a function of how long it stayed in the colon, because the colon is where water is absorbed. So, the less time the food got to stay in the colon, the wetter it will be.

Unfortunately for your cat, it will experience severe cramps if it has diarrhea. These cramps are muscle spasms, the purpose of which is to push the food along the gut quicker.

3) Vomiting

cat throwing up
Your cat may bring up some of the dairy it drank/ate.

Your cat’s body may also tell it to vomit. This happens just in case the cat ate any more dairy which has yet to be digested, which is possible.

This is like dealing with the problem before it becomes a problem. Because the food isn’t allowed to reach the colon, it won’t have any negative effects. It’s only when in the large intestine that the bacteria can break it down to cause gas, as it’s in the large intestine that most of the gut bacteria live.

Your cat can experience these symptoms as a result of something other than lactose intolerance. As such, you can perform a quick test to see if an intolerance is the problem. Feed your cat its normal diet for a week, and see if it experiences gas, diarrhea or vomiting. If not, feed it some dairy, and gauge its reaction. If they result, then lactose intolerance is to blame.

Is It OK For Cats to Drink Milk?

If your cat isn’t lactose intolerant, then you can feed it milk, but it’s not optimal for your cat’s health. It would be better if you gave it regular water, instead (and of course normal cat food).

Symptoms of Lactose Intolerance are Unpleasant

Your cat will experience the same symptoms of lactose intolerance that a person would. These include intense stomach cramps, diarrhea and gas. These are just as unpleasant for your cat to experience as they are for a person to experience.

These symptoms can have knock-on effects, diarrhea in particular. Diarrhea occurs when the gut forces out food that it hasn’t finished digesting, because there’s something it has to get rid of (like bad bacteria, or undigestible food). Diarrhea can therefore cause malnutrition. This wouldn’t happen if your cat only had a small amount of dairy once, but if it was a regular occurrence, then it could.

Dairy Makes Your Cat Gain Weight

Dairy foods contain lots of fat and protein. For a kitten, that’s a good thing, because the kitten needs extra nutrients to help it grow. But an adult cat doesn’t need all those calories on top of its regular food. And if it eats too many calories-worth of food, it will become overweight. Cats get most of their water from food, and a small amount from drinking water. Adding in a calorific drink instead of water is a bad idea.

These issues apply to other kinds of dairy product aside from milk. Cats shouldn’t drink cream or eat cheese of any kind for the same reasons.

Dairy Is Cow’s Milk

A mammal’s milk is formulated for its offspring. Cow’s milk is no exception: it comprises the exact nutrients that are perfect for baby cows, nothing more, and nothing less.

Cat’s milk has a completely different composition to cow’s milk. It contains roughly 8.7% crude protein and 12.7% fat. That’s far more protein and fat than cow’s milk contains, at abour 3.4% fat and 3.3% protein. That’s good in one way, because it means that if you fed your cat cat’s milk, it would gain even more weight! But it also puts paid to the idea that cow’s milk is something that’s beneficial for your pet.

My Cat Drank Milk: What Do I Do?

If your cat somehow got into the milk, don’t worry. It will be fine.

It will likely experience the effects of lactose intolerance, which it will find unpleasant, but these shouldn’t have any lasting effects. These symptoms typically begin some time around 8 hours after the milk/dairy was ingested, as that’s how long it takes food to reach the colon. They last a few hours and get better after your cat goes to the toilet or brings up any remaining lactose. This isn’t something you can help with, except perhaps to comfort your cat.

Stop Your Cat Drinking Milk

If this is a regular problem, and it’s definitely lactose intolerance, then you shouldn’t allow your cat to drink milk or eat dairy any more. As shown above, it’s not doing your cat any good health-wise. It’s also your job as the owner to ensure that your cat has a long, happy, healthy life and the symptoms of dairy intolerance do nothing to help that.

But if you aren’t feeding your cat dairy, and it’s finding access to dairy on its own, take steps to ensure that it can’t do that any more. If somebody in another home is leaving milk out for your cat, either have a word with them, or keep your cat indoors. Or, if your cat is finding dairy products in the bin, get a bin with a lid that your cat can’t get into. Otherwise, these symptoms will continue.

Talk To a Vet

If for whatever reason your cat experiences a severe reaction, you should take it to the vet. They can properly diagnose the problem and recommend a potential fix.

Can Cats Drink Lactose-Free Milk?

You could feed a cat lactose-free milk, but there’s little point.

Yes, cats enjoy milk, but they enjoy all sorts of things that are good for them (like fish). There’s nothing special about milk that cats crave or need, it’s simply a high-fat, dense food, and cats enjoy most kinds of high-fat dense food.

On top of that, milk is bad for cats beyond the issue of lactose intolerance. Your cat should get all the nutrients it needs from its food: lots of fat and protein, a small amount of carbohydrate, and all the minerals and vitamins it needs for maintenance of health. In giving your cat milk, especially high-fat milk, you run the risk of making your cat gain weight.

Hi! My name is Jamie Fallon. I run Catmart, an online cat health and cat behavior resource. If I'm not sat in front of my PC—and I usually am—then I'm either spending time with my cats or my other half... Whoever jumps on me or asks me for food first!

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