When Milk Makes Kitties Sick. The Truth About Cats and Lactose


Lactose intolerance is a condition where cats have difficulty digesting lactose, the sugar found in milk and dairy products. This happens because as cats mature, they produce less of the enzyme lactase which is needed to break down lactose in the digestive system.

Understanding lactose intolerance in cats is important because milk and dairy are common components in many cat foods and treats. Feeding milk and dairy products to a lactose intolerant cat can lead to digestive upset and other health issues. Knowing whether a cat may be lactose intolerant can help pet owners adjust their diet accordingly and avoid unnecessary discomfort.

In this article, we will examine the prevalence of lactose intolerance in domestic cats, what causes it, symptoms to look out for, how it is diagnosed, dietary adjustments for management, other possible treatments, what the outlook is for lactose intolerant cats, and how lactose intolerance can be prevented.

Prevalence of Lactose Intolerance

Lactose intolerance is highly prevalent in domestic cats, with 75-95% of adult cats unable to properly digest lactose due to low levels of the enzyme lactase. However, the prevalence varies depending on the cat’s breed and age.

When cats are kittens, their bodies typically produce enough lactase to properly digest their mother’s milk. However, lactase production decreases significantly after weaning. By adulthood, most cats’ lactase levels are very low. Certain breeds like Siamese cats tend to retain higher lactase levels into adulthood compared to other breeds.

According to a 2019 clinical study, over 95% of adult domestic shorthair cats exhibited symptoms of lactose intolerance when given lactose-containing dairy products regularly. Another study found 75% of randomly sampled adult cats were lactose intolerant. So while exact percentages vary across studies, it’s clear the vast majority of adult cats cannot properly digest lactose.[1][2]

Causes of Lactose Intolerance

Lactose intolerance in cats is caused by a lack of the enzyme lactase, which is needed to properly digest the milk sugar lactose. Lactase breaks down lactose into simpler sugars that can be absorbed into the bloodstream. Kittens produce abundant lactase as they nurse from their mothers in the first few weeks of life. However, as kittens grow into adulthood, lactase production decreases dramatically (Source).

Without adequate lactase, undigested lactose travels to the large intestine where it is fermented by gut bacteria. This fermentation process produces gas, leading to uncomfortable symptoms of lactose intolerance. Essentially, the cat’s digestive system is not adapted to properly break down and utilize the lactose found in dairy products. The lack of the lactase enzyme needed to digest lactose makes the majority of adult cats lactose intolerant.


Cats with lactose intolerance can experience a variety of gastrointestinal symptoms after consuming milk or dairy products. Some of the most common symptoms include:

  • Diarrhea – Loose, watery stool is a hallmark symptom of lactose intolerance in cats. The undigested lactose draws water into the intestines, resulting in diarrhea. The diarrhea may contain mucus or blood in severe cases.

  • Vomiting – Some lactose intolerant cats may vomit repeatedly after consuming milk. The vomiting is often accompanied by nausea.

  • Gas and flatulence – Since cats lack the enzyme lactase to properly digest lactose, the undigested lactose ferments in the colon producing excessive gas. This can result in increased flatulence, burping, and abdominal bloating.

  • Abdominal pain and discomfort – The gas, bloating, diarrhea and vomiting leads to abdominal cramping and discomfort in lactose intolerant cats.

  • Constipation – Some cats may experience constipation rather than diarrhea. The undigested lactose can slow down intestinal motility leading to constipation.

The severity of symptoms depends on the individual cat and amount of lactose consumed. Kittens may better tolerate lactose than adult cats. But all cats have limited ability to digest lactose.


There are a few ways vets can test for and diagnose lactose intolerance in cats:

Blood tests – Vets may check blood glucose levels before and after ingestion of lactose to see if there is a spike, which can indicate lactose intolerance. They may also test for low calcium levels, which can occur with lactose intolerance.

Breath tests – Vets can measure hydrogen and methane levels in a cat’s breath after consuming lactose. Elevated levels indicate improper digestion and lactose intolerance.

Stool sample tests – Fecal samples may be examined for presence of undigested lactose.

Elimination diet trial – Vets may recommend removing lactose from the cat’s diet for 2-3 weeks to see if symptoms improve. If so, lactose intolerance is likely.

Intestinal biopsies – Biopsies of the small intestine can check for damage to the villi, which impairs lactose digestion. This confirms lactose intolerance.

Overall, vets diagnose feline lactose intolerance through clinical signs, lab tests, elimination diets, and biopsies. The main goal is to definitively tie symptoms to lactose consumption.

Dietary Management

The primary treatment for lactose intolerance in cats is to switch them to a low-lactose or lactose-free diet. As cats age and their lactase production decreases, avoiding milk and dairy products can help prevent gastrointestinal upset. There are many commercial cat foods specially formulated to be lactose-free, containing alternative sources of nutrients found in dairy. According to the TabbyEmpire, “By giving your Tabby cat a lactose-free diet, you can help them avoid potential stomach upset and promote overall health and wellness.” [1] It may take several weeks on the new diet for symptoms to fully resolve. Shelters recommend a strict adherence to a lactose-free diet when transitioning lactose intolerant cats. [2]

Other Treatments

In addition to adjusting the diet, there are some other potential treatments for cats with lactose intolerance:

Probiotics may help improve digestion and reduce symptoms. Certain probiotic strains like Enterococcus faecium can produce lactase, the enzyme needed to properly digest lactose. Giving a cat a probiotic supplement or food with added probiotics may help provide some relief.

Lactase enzyme supplements can also be given. These provide the lactase enzyme that breaks down lactose into simpler and more digestible sugars. Supplementing with lactase may allow cats to better tolerate small amounts of dairy products.

According to Wag Walking, some veterinarians may recommend trying digestive enzymes or giving antacids to help manage gastrointestinal upset related to lactose intolerance.

In some cases, antibiotics may be prescribed short-term if secondary bacterial overgrowth occurs in the intestines as a result of lactose intolerance.


With proper diagnosis and management, the outlook for lactose intolerant cats is generally good. While lactose intolerance is a lifelong condition, most cats can live normally with dietary adjustments to avoid milk and dairy products.

The prognosis for lactose intolerant cats is usually excellent when they are fed a lactose-free diet. As long as dairy products are eliminated, most cats will not have any symptoms or gastrointestinal issues. It’s important for cat owners to check ingredient labels carefully and avoid any foods containing milk, cheese, yogurt or other dairy ingredients.

For kittens, recovery from transient lactose intolerance is usually quick once the gut matures enough to produce adequate lactase. Kittens generally outgrow lactose intolerance by 12 weeks of age. For older cats with primary or secondary lactose intolerance, avoidance of lactose is necessary lifelong.

With proper management, most lactose intolerant cats can live a full, healthy and active life. It’s important for owners to provide a nutritionally balanced lactose-free diet and monitor their cat’s condition. As long as dairy is avoided, the prognosis is good.


There are a few ways cat owners can help reduce the risk of their cat developing lactose intolerance:

  • Avoid giving cats cow’s milk or dairy products after weaning. According to the Kitty Creative Company, kittens can typically tolerate some lactose until they are weaned, but their bodies stop producing lactase as they mature, leading to intolerance.1
  • Choose lactose-free cat foods and treats. Many commercial cat food brands now offer lactose-free options formulated for cats with lactose intolerance.
  • Provide lactase supplements if prescribed by your veterinarian. Adding lactase can help improve digestion of dairy.
  • Switch to goat’s milk as an alternative. Some cats are able to better tolerate goat’s milk compared to cow’s milk.

While lactose intolerance is common in cats, limiting exposure to dairy products can help prevent symptoms from developing.


Lactose intolerance is very common in domestic cats, with the majority unable to properly digest lactose after weaning. Cats lack the enzyme lactase which is needed to break down lactose sugar in milk. Consuming milk and dairy products can lead to digestive upset and diarrhea in lactose intolerant cats.

While lactose intolerance cannot be cured in cats, it can be effectively managed through dietary changes, like switching to lactose-free milk and dairy products. Occasional small amounts of regular dairy may be tolerated, but lactose should not make up a significant part of a cat’s diet. Check with your vet before making any major dietary changes.

Understanding feline lactose intolerance allows cat owners to make informed choices about diet and nutrition. By avoiding lactose and providing digestible alternatives, cat owners can help their lactose intolerant cats live happy, comfortable lives.

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