I’ve celebrated the goodness of dairy fat  quite enthusiastically in recent weeks. If you were just joining us, you might have gotten the wrong impression that you’d stumbled into a PR wing of the dairy industry, and that the streets of Mark’s Dairy Apple run whitish-yellow with grass-fed  milk fat. No, children aren’t busting open fire hydrants on warm days to dance around in the effervescent spray of kefir , and on winter days it doesn’t rain milk and snow globs of thick Greek yogurt in these parts.
I’m well aware of the darker side to dairy, and today I’ll be exploring the common arguments against dairy consumption. Let’s jump right in:
Grok didn’t drink milk.
True, but the evolutionary argument cannot prove the suitability or unsuitability of a food – it can only generate hypotheses that we can then test or research. The same goes for grain consumption , nighttime artificial light exposure , sedentary living, or any other evolutionary novel activity. It has to be tested.
Takeaway? The relative newness of dairy in the human diet definitely raises concerns about its healthfulness, but it’s not a resounding argument in and of itself.
We’re the only species that drinks the milk of other mammals.
It does seem a bit weird. That’s mankind, though: we do weird things that no other animal could ever conceive of doing. That’s what makes us the top of the food chain. We’re smart and dominant enough to impose our will on nature . It gets us into trouble – see industrial agriculture  and artificial trans-fats  – but it also improves our station – see the decision of hominids three million years ago to “see how this dead herbivore flesh tastes.” Like the previous argument, this one can only raise hypotheses.
Takeaway? Our species’ departure from, or modification of mammalian norms isn’t always bad. Or good. The specifics matter.
Dairy raises insulin.
It’s true, it does. Both the lactose and dairy proteins exert an insulinogenic effect that when taken in concert rival that of many carbohydrate sources. I actually covered this topic in a post several years ago  and found that acute dairy-induced spikes of insulin don’t seem to be related to body fat gain or insulin resistance in healthy people, and that the studies showing a connection between dairy and insulin resistance used skim or low-fat milk, rather than whole. And in athletes trying to recover from training, these insulin spikes may actually promote recovery. Hyperinsulinemia, where insulin is chronically elevated, is another story. If you’re already insulin-resistant, dairy  could be problematic.
Takeaway? Dairy’s insulinogenic effect is good for some groups (lean, insulin-sensitive, athletes or trainees looking for muscle recovery), bad for others (insulin-resistant). Context is important.
The betacellulin in dairy can increase cancer.
Betacellulin is a growth factor found in whey that plays an important role in infant growth. In some in vitro studies, isolated betacellulin has been shown to contribute toward the growth of cancer cells. Chris Masterjohn takes apart this argument  fairly well, explaining how similar in vitro studies that incorporate conjugated linoleic acid (a trans-fatty acid especially abundant in pastured dairy fat) show that CLA  has an inhibitory effect on the promotion of cancer by betacellulin; how most epidemiological studies show no relationship between commercial milk and cancer; how some only support a relationship between low-fat dairy and ovarian and prostate cancer, but not high-fat dairy; and how whole fat milk is actually associated with a lower risk of colorectal cancer.
Takeaway? If betacellulin has cancer-promoting tendencies, it’s probably only when isolated from protective dairy compounds such as CLA and saturated fat . Stick to full-fat, pastured dairy.
Dairy is a general growth promoter and can increase cancer.
Loren Cordain and Pedro Bastos (with a couple other collaborators) released a very interesting paper  in which they suggest that rather than being just food, milk is an “endocrine signaling system” whose various components – particularly the proteins – are meant to stimulate hormonally-driven growth in a “species-specific” manner. So human breast milk is perfect for how human babies are supposed to grow and tissue differentiate, cow milk is ideal for calf growth, goat milk for kid growth, and so on. Milk proteins stimulate growth by activating the mTOR pathway and stimulating IGF-1 release. Cordain and Bastos link dairy-induced mTOR activation and IGF-1 release with prostate cancer, citing in vitro and epidemiological evidence that milk consumption during certain developmental phases (prenatal, immediately postnatal, and adolescence ) can predispose developing prostates to cancer later in life.
More generally, IGF-1 is a growth promoter which is elevated in childhood – because that’s when people are growing at a fairly steady rate – and in certain types of cancer  – because that’s another kind of growth, only unwanted. Since dairy protein consumption is pretty consistently linked to increased IGF-1 , it’s easy to assume that dairy can increase cancer risk. Good for growing bodies, bad for growing cancer cells.
So, people with cancer or at risk of cancer should avoid dairy, right? I’m not sure. This study  found that a whey protein supplement actually increased the vulnerability of cancer cells to chemotherapy among patients with carcinoma. Another study  identified several potential roles for milk proteins in cancer prevention. And there’s the classic tale of Campbell’s rats, where high-casein diets were protective against the development of aflatoxin-induced cancer  but increased cancer progression once initiated.
Plus, the mTOR pathway is also where muscle growth happens, which may be why GOMAD  (gallon of milk a day) is a popular tactic for strength trainees.
Takeaway? Dairy is a growth promoter, which can be good (muscle) or potentially bad (cancer, particularly prostate when consumed at certain developmental stages). It’s unclear if dairy actually promotes tumorigenesis or promotes growth only once the cancer has been established – or neither.
Dairy increases intestinal permeability, thus allowing proteins and other bioactive compounds entrance into the bloodstream. This can precipitate or exacerbate autoimmune diseases.
For years, I’ve heard that “dairy is designed to increase intestinal permeability.” After all, infants need a bit of a leaky gut to allow absorption of large things like colostrum. It would make sense for milk to increase permeability so this could happen. But it turns out that infant guts are innately permeable, not permeable because of dairy. If anything, it looks like dairy might actually make guts less permeable. I didn’t find any human research to this effect, but I did find some interesting studies with surprising results:
Hydrolyzed casein restored intestinal barrier function  and prevented diabetes in a diabetes-prone rat. A later study  confirmed these results. A specific casein peptide was also shown to reduce intestinal permeability in another study, and beta-lactoglobulin (another protein component of dairy) had similar effects  on intestinal tight junction function. And finally, a component of whey has also been shown to reinforce tight junction integrity .
Yeah, I was surprised too.
That doesn’t mean there aren’t connections, even causal, between dairy consumption and autoimmune diseases like type 1 diabetes , but the presence of leaky gut may be a prerequisite. This would jibe with the observations that people with type 1 diabetes , multiple sclerosis , rheumatoid arthritis , and other autoimmune diseases sometimes linked to dairy intake have higher intestinal permeability.
Takeaway? Although these were either rodent or in vitro studies using isolated components of dairy, it seems like the evidence points toward dairy upholding intestinal integrity , if anything. Given existing permeability, dairy proteins can slip through and obviously cause problems, but I’m unaware of evidence showing they increase leaky gut or autoimmune disease on their own absent intestinal permeability.
Dairy has a high acid load, which can lead to bone calcium loss.
I’ve always been skeptical of this one because using the same criteria, meat also has a high acid load on the body. Should we forgo eating meat, which has been shown to improve bone mineral density ? Plus, one recent study  found that dairy doesn’t actually make the body acidic. Milk and dairy products “neither produce acid upon metabolism nor cause metabolic acidosis.” Further, dairy is a good source of calcium  and – particularly in the case of gouda cheese – vitamin K2 , both important co-factors in bone metabolism.
Takeaway? Dairy consumption may not ensure or be necessary for good bone health, but it doesn’t seem to negatively impact it.
Dairy contains ample amounts of bioactive hormones which can have negative health effects.
Since a common practice nowadays is the milking of pregnant cows in order to maximize production and estrogen goes up during pregnancy, it seems reasonable to expect elevated levels of estrogen in dairy. Most studies I came across found that some estrogen  is present in dairy, with skim milk containing the most bioavailable form of estrogen  (conjugated estrogen, the same kind used in oral hormone replacement therapy). For the most part, the amount of active estrogen found in dairy seems too low for physiological relevance . We have too much already in circulation for it to be impacted by dietary sources, some of which will be nullified by digestion.
Dairy proteins can certainly increase IGF-1 (as shown previously) in people, but it’s unclear whether the actual IGF-1 found in dairy has an effect on serum levels. If you’re worried about IGF-1, fermentation takes care of most of it . Stick to fermented dairy like yogurt , kefir, or cheese  (which already has health benefits  over regular unfermented dairy).
Takeaway? Hormone levels in dairy vary according to production method, pregnancy status of the animal being milked, and chance. For the most part, the amount of hormones in dairy pales in comparison to the endogenous amounts circulating in our bodies at any given time, so even if we had the leakiest gut in the world and everything we ate was absorbed directly into our blood, it would likely have minimal impact on our hormone levels.
Dairy causes acne.
Among food-sensitive acne sufferers, dairy is probably the most commonly reported offender. Indeed, recent studies suggest a connection between skim milk consumption and acne in teenage boys  (less so for whole milk) and in girls . Researcher Bodo Melnik points the finger  at the mTOR/IGF-1 activating qualities of dairy (and the Western diet at large) as the culprit. It’s a compelling line of argument.
However, one recent study  found that fermented dairy enhanced with lactoferrin reduced the incidence of acne, suggesting that dairy isn’t always antithetical to skin health. Raw dairy might work better than pasteurized dairy, since pasteurization destroys the natural lactoferrin content of milk.
Takeaway? Dairy is a common aggravator of acne  and is worth removing or avoiding if you have it.
That bovine serum albumin in dairy resembles human collagen type 1 and can increase rheumatoid arthritis through molecular mimicry.
Rheumatoid arthritis patients do seem to produce antibodies to bovine serum albumin , and one case study  found that an RA patient achieved relief with cessation of milk consumption and saw symptoms return with resumption. Still, another more recent paper  found that BSA antibodies weren’t associated with disease progression or activity (flare-ups) in rheumatoid arthritis, so it’s still theoretical. I would imagine that the problem (if extant) is exacerbated by the presence of leaky gut.
Takeaway? Seems worrisome enough that people with RA might try avoiding dairy, at least as a trial to see how it affects their symptoms. One confounder is that bovine serum albumin is also found in beef muscle meat. RA patients who are reading this: do you notice problems with beef?
Overall, it appears that dairy has both benefits and risks, and that where you fall depends on several factors, like gut health, insulin sensitivity, activity level, age, as well as the quality and form of the dairy (which though I didn’t really get into are implicit when discussing dairy). In other words, it’s extremely variable and personal.
What do you think, folks? Any other anti-dairy arguments out there? Let me know in the comment section!