4 Good & Bad Ways Dairy Affects Your Gut Health

The first dairy product many of us encounter is breast milk, and it's a unique kind of dairy. A study from 2016 found that breast milk produces bacteria in the gut of babies that helps to protect them and their developing immune systems. "Human breastmilk transmits lactoferrin, an iron-binding glycoprotein, to protect the undeveloped infant gut from pathogen colonization," noted Science in 2018. And in 2017 scientists discovered that there's one gut bacterium, Bifidobacterium longum, that evolved to survive on a sugar only found in breast milk.

Breast milk actually produces a different gut bacteria population: if you're breastfed, you'll have a specific gut microbiome that's different from people who were fed on formula. It's not thought that this has a big effect on human health, but it does show that breast milk has evolved to have a very specific effect on infant guts from the moment we're born.

Dairy contains several different elements that can influence the health of your gut. The protein most commonly found in dairy is called casein, which can be taken as a supplement to help muscle growth and is, according to Healthline, "highly underrated" when it comes to human health, because it breaks down very slowly in the gut and fuels cells for a long period of time. The other protein found in dairy is whey, of Miss Muppet fame, and it doesn't seem to have the same gut benefits as casein.

Casein, studies have found, has a lot of branched chain amino acids, or BCAAs. The more BCAAs you have in your gut, the higher your levels of Akkermansia and Bifidobacterium bacteria, and the 'younger' your gut microbiome appears (yep, it shows age like the rest of us) — but scientists aren't entirely sure what links these things, so don't take casein supplements without taking a doctor's advice first.

A lot of the positive press around dairy products and gut health revolves around fermentation. Studies have shown repeatedly that fermented dairy products such as kefir and yogurt carry probiotics, or compounds that boost bacterial growth, and ingesting those can help with gut health. In fact, a study in 2015 found that dairy is one of the best vehicles for 'carrying' probiotics into the body.

So what can fermented milk products do for the gut? A study in Nature in 2014 found that eating fermented milk products increased gut production of butyrate, which is known to help gut health, and decreased Bilophila wadsworthia bacteria, which is linked to intestinal issues like IBS. Fermented dairy products also reduced gut hypersensitivity in rats in a 2012 study. If you do love dairy, it's good to focus on these aspects of the dairy product spectrum to help your gut flourish.

Moderation may be the name of the game when it comes to dairy intake. A 'Mediterranean diet' — which involves lots of "olive oil, assorted fruits, vegetables, cereals, legumes, and nuts; moderate consumption of fish, poultry, and red wine; and a lower intake of dairy products, red meat, processed meat and sweets" — has been shown to be most beneficial for the gut microbiome; a 2017 study noted that Western diets high in red meat and dairy "led to a marked decrease in numbers of total bacteria and beneficial Bifidobacterium and Eubacterium species" in the gut.

A lot of evidence shows that diets high in meat and dairy make the gut less balanced. A study in Nature in 2015, for instance, showed that "rats fed with meat proteins and casein had significantly lower levels of lipopolysaccharide-binding proteins, suggesting that the intake of meat proteins may maintain a more balanced composition of gut bacteria". This isn't great for overall health, from the immune system to digestion. Science says don't max out on dairy intake to make sure your gut can flourish.

There's no one-size-fits-all prescription for how dairy affects gut health, because there are so many aspects to both dairy's composition and the gut microbiome itself. Consuming dairy products, for instance, is linked to the production of trimethylamine N-oxide in the gut, and high levels of that substance have been shown to be a good indicator of future heart health problems. We don't only get trimethylamine N-oxide from dairy; it also comes from the consumption of red meat and eggs. However, it's not really a plus on the side of dairy.

On the other side of the equation, there's vitamin K. Virtually all of the vitamin K in the human body is produced in our guts, and it's essential for human health, particularly for blood clotting. A study in 2017 found that dairy products actually contain high levels of a particular kind of vitamin K called menaquinones, and that's likely where most US adults get their vitamin K from. Full-fat dairy products, particularly soft cheeses, milk and yogurts, had high concentrations of vitamin K. Consume some of those, in other words, and you're prompting vitamin K production in your gut and helping your blood clotting.

When it comes to gut health, dairy is a mixed bag; it helps in some ways and appears to hinder in others. If you do want to cut dairy from your diet, make sure you do your research on replacements that will help gut function and vitamin levels; otherwise, focus on fermented and cultured products like tasty kefir and Icelandic skyr to boost your bacterial population.