Lactose Intolerance In Dogs

Joanne Keenan
Lactose Intolerance In Dogs

Ever wonder why some dogs can eat dairy and others can’t?

Dogs may love dairy products like cheese … but some get digestive upsets with diarrhea, vomiting, or even lethargy. 

That’s because dairy products contain lactose … the natural sugar in milk. But like people, many dogs are lactose intolerant. Their digestive systems can’t break down lactose. Dogs, like most mammals, require lactase, a digestive enzyme, to digest lactose. But not all dogs produce it … or enough of it. 

There’s less lactose in cheese than milk … so that’s why it might seem like cheese is okay for some dogs, but they still react to milk.

So here’s some background on lactose intolerance in dogs and why dairy can make your dog sick.

History Of Lactose Intolerance In Mammals

It’s actually perfectly normal for your dog to get sick from eating dairy products. According to animal nutritionist Dr Richard S Patton PhD, it’s only through centuries of genetic adaptation that humans have retained the digestive enzyme lactase that allows them to digest milk as they enter into adulthood (1). 

Several studies point out that after weaning, in most mammals there is a genetically programmed decrease in lactase production that gradually occurs (2). And in fact, about 70% of the world’s adult population displays this reduction of lactase. Yes, 70% of the adult world population is lactose intolerant (3). And within some countries like Sweden and Finland, it can be as high as 75-82%. According to the National Institutes of Health (NIH), lactose intolerance shows up most often in people of Asian and African heritage … where it affects 70 to 100% of these populations (4).

The Vuorisalo study of 2012 concluded that lactose intolerance is higher in countries where cattle herding was not widespread and fresh cow milk was not been part of the traditional diet … such as in northern Europe, Sweden, Finland and Asian countries (5).

Dr Patton says the ability to maintain the production of lactase at maturity is “lactase persistence.” It came into existence 3,000-7,000 years ago when an additional set of genes kept lactase production switched on in the body. This allowed people to consume dairy from their herds past their infancy and well into adulthood. It’s a genetic adaptation that spread quickly among African cattle-herding people. A parallel adaptation happened in Northern Europeans even sooner (6).

So centuries ago, all humans were lactose intolerant after weaning. And today some are missing the gene that allows them to digest lactose. So it’s actually normal for people not to be able to digest dairy … and dogs, too.

Lactose Intolerance In Dogs

A similar process of lactase persistence is at work in dogs. Puppies have lactase in abundance while they’re nursing. But it should wane as they are weaned. They might not be able to digest cow or goat milk in later life unless lactase persistence occurs. So essentially, mature dogs aren’t built to eat dairy products once they’ve been weaned from their mothers … especially dairy products from another animal.

If your dog is lactose-intolerant, lactose found in milk and other dairy products will pass right through his gastrointestinal tract undigested. When it reaches the colon, the undigested sugar will attract water and cause diarrhea. This leads to fermentation of bacteria that’s present in the colon, which can cause gas, bloating and discomfort.

Signs of Lactose Intolerance In Dogs

Dogs can have minor degrees of lactose intolerance … usually because of a low lactose level in what they’ve eaten. But dogs with high lactose intolerance experience the same type of symptoms as people. And that can produce more severe symptoms such as:

  • Loose stools
  • Bloating, flatulence and discomfort
  • Abdominal pain
  • Diarrhea
  • Nausea
  • Vomiting

Symptoms can begin 30 minutes to 2 hours after eating foods with lactose. 

Can Dogs Eat Dairy?

So yes, dogs who produce lactase can eat some dairy products like cheddar, parmesan and swiss cheese that have low amounts of lactose. If your dog can tolerate dairy, you can share some cheese with him in moderation. You definitely want to avoid dairy that’s high in fat and sugar … especially sweetened yogurt.

According to the American Kennel Club (AKC), “Milk is a safe treat in small quantities.” If you feed your dog a few tablespoons of milk he might be fine. But if he reacts with any of the above symptoms, it’s best to keep dairy to yourself. And sometimes large amounts of dairy can give your dog an upset tummy even if he’s not lactose-intolerant. 

In a study by Gallagher et al in 1974, researchers suggested that yogurt had a lower lactose content than milk (7). But in fact they determined it was the bacteria content in yogurt that metabolized the lactose. The lactose content between yogurt and milk was actually very similar. And a 1997 German study by Sieber et al also found that yogurt is very well tolerated by those who are lactose intolerant because of the higher presence of lactase, plus the presence of living lactic acid bacteria. The bacteria in fermented dairy products survives passage through the stomach to continue the digestion of lactose. (8)

But some dairy products contain too much fat … and that can also lead to diarrhea and vomiting. High fat can also lead to pancreatitis, a serious disease, as well as obesity

While low-fat or fat-free options seem like a good idea, you should avoid them. These products have gone through processing that often involves chemicals. Some low fat products also contain more sugar. They can lead to overeating because of a false sense of security in having a non-fat option for your dog. And they can increase the risk of diabetes and obesity. 

But there are probably more reasons for your dog to avoid dairy.

Why Dogs Shouldn’t Eat Dairy

So even if your dog can tolerate dairy, is it still okay to feed it to him? Well … you might not see diarrhea or vomiting but there could be other signs that aren’t as noticeable. But they can all be traced back to dairy.


Chronic inflammation leads to skin problems, digestive issues and most disease. And dairy products are pro-inflammatory. They have inflammatory properties that include proteins, hormones and sugar … especially whey proteins. So whether it’s an allergy or lactose intolerance, dairy can create chronic inflammation in your dog and lead to serious health issues. 

Leaky Gut

As noted earlier, undigested lactose from dairy can settle in your dog’s colon and cause fermentation of bacteria. That can disrupt the balance of your dog’s microbiome with bad bacteria and lead to disease. So if your dog often eats dairy repeatedly and doesn’t digest it properly, it can cause ongoing intestinal problems. If the aggravation continues it can damage the intestinal lining of the gut and cause leaky gut. So if your dog is eating a processed food diet, taking medications and is over-vaccinated, they all take their toll on his gut. And dairy could be doing more harm than good. 


Yeast thrives on sugar and carbs so that includes the sugars in milk. Lactose in milk is a form of sugar. To get rid of yeast you need to starve it and eliminate all forms of sugar. Avoid all milk and dairy products for a dog with yeast infection.


A dog with a dairy allergy will have the typical allergic signs:  

  • Itchiness
  • Itchy ears
  • Hives
  • Swelling
  • Skin issues, hair loss and rashes

These can be from an allergy or intolerance to milk so if you stop feeding dairy, they should go away. But if the problem has been ongoing, it can lead to secondary complications and you could be dealing with something more chronic like inflammation, yeast or leaky gut.

Unsafe Additives

Milk and dairy products undergo many forms of processing. Unless it’s a raw product, you need to be aware of additives like these that can harm your dog.

  • Salt. It helps age cheese but too much salt can lead to dehydration in your dog.
  • Added ingredients. MSG and products used to smoke cheeses can be carcinogenic.
  • Processing. Products like cheese slices can contain artificial flavors and colors … and chemicals like sodium phosphate and titanium oxide for color that can lead to health problems.
  • Mycotoxins. They’re found in ripe, moldy cheeses and can cause poisoning in dogs. 

So if you still want to feed your dog dairy, you need to choose the right products.

What Kind of Dairy Can Dogs Eat?

If your dog can tolerate dairy and you want to feed him a little, choose raw, organic grass-fed milk and dairy products

Raw milk has a higher lactase content which helps digest the lactose. Choose milk products from grass-fed, pasture-raised cows that weren’t fed antibiotics, GMO foods or pesticides. Organic dairy products are generally lower in saturated fats, have more protein and have a healthier balance of omega-3 and omega-6 fatty acids

Goat milk and fermented goat milk are better options than milk from cows. Goat milk lacks the kind of casein that can cause inflammation in your dog. Unpasteurized goat milk has both probiotics and prebiotics (oligosaccharides) to support your dog’s gut health (9). 

If your dog has a healthy gut, then feeding him fermented goat milk is also a better idea. It’s richer in prebiotics to nourish the good bacteria in his gut. And it’s got postbiotics to stop harmful bacteria from growing, boost immunity and reduce inflammation. And fermented dairy products are easier for your dog to digest because they’ve already got more enzymes for digestion and absorption of nutrients. But if you’re dealing with yeast issues, it’s best to avoid fermented foods. 

So … knowing that dogs were not genetically designed to eat dairy beyond puppyhood makes you wonder if there’s any reason they should … unless it’s mother’s milk. Why risk it when there are so many other healthy, dog-friendly treats to give him?


1. Patton, Richard S. Ruined By Excess, Perfected By Lack. DN Publishing. 2017.

2. Gerbault P, et al. Evolution of lactase persistence: an example of human niche construction. Philos Trans R Soc Lond B Biol Sci. 2011 Mar 27;366(1566):863-77.  

3. M. Corgneau, et al. Recent advances on lactose intolerance: Tolerance thresholds and currently available answers. Critical Reviews in Food Science and Nutrition. 2017. 57:15, 3344-3356

4. Lactose Intolerance By Country. Britannica

5. Vuorisalo T, et al. High lactose tolerance in North Europeans: a result of migration, not in situ milk consumption. Perspect Biol Med. 2012;55(2):163-74.  

6. Gerbault P, et al. Evolution of lactase persistence: an example of human niche construction. Philos Trans R Soc Lond B Biol Sci. 2011 Mar 27;366(1566):863-77. 

7. Gallagher CR, Molleson AL, Caldwell JH. 1974 Lactose intolerance and fermented dairy products. J Am Diet Assoc. 1974 Oct;65(4):418-9.

8. Sieber, al. Lactose intolerance and consumption of milk and dairy products. Z Ernährungswiss. 36, 375–393, 1997. 

9. van Leeuwen SS, Te Poele EM et al Goat Milk Oligosaccharides: Their Diversity, Quantity, and Functional Properties in Comparison to Human Milk Oligosaccharides. J Agric Food Chem. 2020 Nov 25;68(47):13469-13485.

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