Thursday, March 17, 2011

What About Dairy?


I'm exaggerating (a little). But we've gotten a couple of testy emails from hyper-orthodox Paleo readers who check out M's site and freak out over the trace amounts of dairy that remain in our diets. To them, I have this to say:

Please chill out.

It's been a long time since I last wrote at length about milk. And in that time, our dairy consumption has dramatically decreased. Cutting out grains and added sugar already meant getting rid of many of our favorite dairy-delivery vehicles, like breakfast cereals, pizza, grilled cheese sandwiches, frozen yogurt and ice cream. We stopped buying big tubs of fresh mozzerella di bufala, and I no longer devour huge plates of cheese. I don't drink milk (and haven't since I was a kid), and I take my coffee black. And M managed to abstain from dairy altogether during her month on the Whole30.

But we do still eat a small amount of dairy from time to time, including pastured butter, ghee, and a bit of cheese and full-fat Greek yogurt. Frankly, this is a personal choice. We're not saying that you ought to follow our example, or that cow juice is super-awesome for you. We're continuing to learn from others about the physiological effects of the stuff, and it's very possible that one day, we'll decide to eliminate all dairy from our diet. But given that we continue to receive questions about why bovine dairy still pops up in M's recipes, I thought I'd explain our current thinking behind the decision not to go cold-turkey.

In a nutshell:
  • We don't care that cavepeople didn't drink cow's milk.
  • There are proposed mechanisms that suggest that cow dairy is bad for you.
  • But there's still a lack of consensus -- even within Paleo circles -- about whether full-fat dairy actually poses health risks to folks without leaky gut or other autoimmune issues.
  • Plus, on the whole, there may actually be a net benefit to eating some high-quality, full-fat dairy.
  • Still, to be on the safe side, we've cut out most dairy -- but we've made room for certain exceptions.
Let's take these one by one (after the jump)...

We're Not Shooting for a Historical Reenactment

As Kurt Harris has pointed out, some strict Paleo eaters are adamant that we all should avoid dairy 'cause it's a Neolithic food: Cavemen didn't eat it, so we shouldn't, either. This is an argument that Pedro Bastos and Loren Cordain, among others, have raised:
There is a large body of evidence that up until 9,000 years ago in the Middle East and 7,000 years ago in Northern Europe, no human being on the planet consumed non human milk or dairy products. So on an evolutionary time scale, non-human milk is a relative newcomer into [the] human diet. By using the evolutionary template, and knowing that that milk is species specific, we would expect this new habit to have unintended consequences.
Fair enough. And Cordain and Bastos do go on to discuss some proposed mechanisms by which dairy could present health problems. But let's just agree to dismiss out of hand the argument that cow dairy must be avoided because it wasn't part of the human diet until a few thousand years ago. As we’ve discussed before, we’re not in the business of historical re-enactment. As Chris Kresser writes:
We can look to the Paleo era to determine what was evolutionarily normal for humans, but it doesn’t follow that anything that falls outside of that norm is automatically harmful. The argument that we shouldn’t eat dairy now because we didn’t eat it 2 million years ago -- without supporting clinical evidence -- is not convincing.
The absence of cow's milk in the diet of our Paleolithic ancestors simply raises a question that needs to be answered with rigorous testing. The pertinent issue is not whether prehistoric man drank milk but whether dairy -- an admittedly modern food -- is in fact harmful to modern humans.

So what does the clinical evidence actually say? Is all dairy evil?

The Bad News About Dairy

Bastos, Cordain and a bunch of other Paleo luminaries have postulated that a host of problems may be caused or exacerbated by dairy consumption, including:
Then there’s the whole A1/A2 beta-casein issue. Long story short: A1 cow dairy – the dominant type in the U.S. = Not good. It’s been connected to all sorts of disorders, including schizophrenia, autism, heart disease and diabetes.

(Want the longer story? Fine. Beta-casein is a protein made up of a chain of 229 amino acids. If the amino acid in the number 67 position is proline, you’ve got beta-casein from an A2 cow, typically a Guernsey or Jersey. If the amino acid is histidine, you’re looking at an A1 cow, like a Holstein or Friesian. Proline tightly bonds to a small protein fragment called beta-casomorphin 7 (BCM 7), which keeps it from getting into the blood or guts of A2 cows. Histidine, on the other hand, releases BCM 7 upon digestion, so it’s often found in the GI tracts of animals and humans who ingest A1 dairy. And BCM 7 exposure has been linked to neurological and immunological impairment. Have your eyes glazed over yet? Hello?)

You can read more about the parade of dairy-related horribles here.

All of this should be enough to scare any reasonable-minded Paleo eater off of dairy forever, right? Well, hold on a minute.

Not Everyone Agrees!

Unlike the case against gluten, not every Paleo-minded thinker agrees that the evidence against dairy is altogether damning.

For example, some argue that the cancer issue may not be so clear. As Mark Sisson put it:
Cordain thinks milk leads to cancer, citing a fairly impressive array of studies that seem to suggest a link between milk consumption and various types of the disease. He fingers betacellulin, one of milk’s epidermal growth factors, as the causal agent. In the fetus and suckling newborn, betacellulin helps with growth and tissue differentiation. It’s completely essential for growing infants. In adults, Cordain says it passes cleanly into the gut, completely intact and free to enter circulation, where it can bind to receptors and enhance cancer cell growth. 
What Cordain doesn’t mention is conjugated linoleic acid (CLA), which is also found in milk fat (especially raw, grass-fed milk, which is never included in any study) and has been shown to possess anti-cancer effects by inhibiting breast cancer cell growth and reducing the activation of insulin-like growth factor receptors (the same receptors Cordain identifies as sensitive to betacellulin). The studies Cordain cites as support of the milk-cancer connection are interesting, but their messages are muddled. 
As Chris Masterjohn points out, milk proteins mostly appear harmful only when separated from their natural fat. Low fat and skim milk appear to have associations with certain cancers (like prostate), while whole milk appears protective (of colorectal cancer) or neutral. It would be nice to see researchers take a good, long look at full-fat, pastured dairy’s effects on cancer rates. Conventional milk consumption probably isn’t advisable, but the jury’s still out on whether raw, pastured, whole milk is also problematic. We need more data.

Similarly, the claim that dairy contributes to obesity and Type 2 diabetes isn't super-straightforward. First of all, some studies indicate that drinking full-fat milk is associated with lower body weight. As for the diabetes issue, Kresser writes:
Cordain’s group has published and reviewed several papers proposing various physiological mechanisms by which dairy causes harm. One recent example is a paper by [Bodo] Melnik called Milk Signalling in the Pathogenesis of Type 2 Diabetes. The theory presented is that milk consumption beyond the weaning period may overstimulate pancreatic beta-cells and promote beta-cell apoptosis. Since proliferation and apoptosis of beta-cells are hallmarks of type 2 diabetes (T2DM), it follows that milk consumption must contribute to T2DM.

Or does it?

If that theory were true, we might expect to see increased rates of T2DM in people consuming dairy products. But in fact we see just the opposite.

This study looked at serum levels of trans-palmitoleic acid, a fatty acid found in milk, cheese, yogurt and butter, and correlated them with risk factors for diabetes. [...The researchers found that] people with the highest trans-palmitoleate levels had 1/3 the risk of developing diabetes over the three years volunteers were followed. Not only that, after adjusting for confounding factors trans-palmitoleate levels were associated with smaller waist circumfrence, lower triglycerides, higher HDL and lower C-reactive protein.
Okay -- but what about the chronic inflammation caused by the casein in dairy? Mark Sisson again:
Paleo opponents of dairy say casein wreaks similar havoc on our guts [as gluten], and it’s true that gluten intolerance goes hand-in-hand with casein intolerance. But is casein a primary cause of leaky gut, or does it slip in only after gluten has opened the floodgates? Once a floodgate is opened, any protein can enter and cause issues. And after all, casein is the primary protein in human breast milk…
Sisson's not alone; this same position has been taken up by Peter over at Hyperlipid (among others). In fact, some studies have found no correlation between dairy consumption and autoimmunity. And other studies indicate that casomorphin doesn't trigger addiction.

Further, while skim milk has been shown to be linked with acne, full-fat milk doesn't appear to have as strong a correlation. (Though if you're desperate to camouflage a big swath of fiery pus-balls on your face in hopes that your prom date won't notice, you should probably stop guzzling milk altogether.)

A quick note about lactose intolerance: I'm really not all that concerned about it. Lactose intolerance is the inability to digest lactose -- a type of sugar found in dairy. A lot of people have it because they can't produce the enzyme lactase, which is necessary for digestion of lactose. But guess what? Milk contains lactase! Or it does until pasteurization, a process that kills the lactase. This isn't a problem with raw milk. (And if you think that raw milk is dangerous and its sellers need to be taken down with armed SWAT teams, just avoid it. Remember: Lactose intolerance may be uncomfortable and stinky, but it's not actually harmful to you.)

In other words, there are more sides to the dairy story than a casual reader of Cordain's "The Paleo Diet" may be led to believe.

That said, there are a couple of issues on which everyone (outside of the dairy industry) seem to agree. First of all, A1 beta-casein still looks like some scary shit. Secondly, if you already have leaky gut syndrome or other autoimmune issues, steer clear of dairy.
If someone has compromised intestinal permeability, or “leaky gut”, it’s more likely that their immune system will respond to potentially allergenic components in milk such as alpha- and beta-casein, casomorphin and butyrophillin. This is especially true for people who are gluten intolerant, because it has been shown that milk proteins commonly cross-react with gluten. Put another way, if you react to gluten, it’s more likely that you’ll also react to milk. Along these same lines, people with small intestine bacterial overgrowth (SIBO) – which is one of the major causes of irritable bowel syndrome (IBS) – may be more likely to react to milk because the bacteria in their small intestine aggressively ferments lactose, the sugar in milk, causing gas, bloating and other G.I. symptoms.

What's So Great About Dairy?

With the insane amount of bad science out there, it's possible to find "evidence" to support just about any hypothesis. Still, it's worth nothing that there's (admittedly epidemiological) support for the argument that dairy may confer some net health benefits to those who choose to ingest it. (The full-fat variety, anyway.) For example:
Again, I'm sure there are plenty of other studies that point to the opposite conclusion. Still, it's worth considering whether avoiding dairy is akin to throwing the baby out with the bathwater.

On Balance, We're Leery of Dairy -- But Not Enough to Avoid It Altogether

So: Is cow dairy harmful for people without autoimmune disorders?


There are some proposed mechanisms for dairy-derived damage. And just like every other food product that's been processed to become "low-fat" or "no-fat," skim and low-fat milk are ridiculous.

Still, there doesn't appear to be a consensus in the Paleo community about the health effects of full-fat, pastured dairy. On the one hand, you have the Loren Cordain/Pedro Bastos/Robb Wolf/Whole9 gang beating the drum against dairy intake, and on the other, you have the Kurt Harris/Mark Sisson/Chris Masterjohn/Chris Kresser/Hyperlipid crew spreading the word that dairy may have gotten a bad rap. Who to believe?

In the end, I think Dallas Hartwig of the Whole9 has made a pretty compelling argument for taking a conservative better-safe-than-sorry approach and avoiding all but the highest-quality, full-fat dairy:
We, too, think high-quality dairy fat is great stuff, but consider conventional milk/cream/butter and most of the milk protein-containing stuff (cheese, yogurt, kefir, etc.) less good. Personally, we avoid it altogether. We do use copious amounts of organic, pastured, clarified butter, and have have nothing but positive experiences. 
So… I guess my take on Dr. [Kurt] Harris’ perspective is that he and I agree on the goodness of dairy fat, but he is less convinced on the downsides of small amounts of dairy proteins, which we tend to avoid. I’m pretty cautious on the inclusion of food that has some evidence against it (even if it’s not completely damning evidence). I feel differently than Chris Kresser who says the burden of proof is to demonstrate beyond a shadow of a doubt that dairy is harmful. 
I prefer a more conservative stance, because after all, it’s that same “burden of proof” argument that let so many people think that smoking was totally fine for you for so many decades, even though there was early evidence that it wasn’t awesome. (Funny how we fight for our vices, eh?) If I see evidence suggesting that smoking might harm me, I’d rather quit smoking now than insist that the evidence against smoking is incomplete and inconclusive. An extreme example, perhaps, but I prefer skipping out on stuff that has serious potential to be harmful, and adding it back in later if it’s proven totally safe.
I tend to agree with this point of view, and have therefore cut out most conventional dairy from my diet. For the most part, we now limit ourselves to high-quality, full-fat dairy in the form of pastured / grass-fed butter and ghee. However, we don't have any autoimmune issues, so you'll see us throwing some full-fat Greek yogurt into a recipe or two because, well, we like it. And just as we don't refuse to eat grain-fed steaks and vegetables stir-fried with canola oil when we're out at restaurants, we're not going to freak out if our salad arrives with a bit of unexpected cheese sprinkled on top. (But we're also not going out of our way to order the cheese plate, either.)

In sum, we're not stressing about this small amount of dairy intake. But it's a personal thing. Are we just making excuses for our casomorphin addiction? Are we lying to ourselves? Are we less than perfectly Paleo? Maybe. But we're just a couple of dumb bloggers. We've been wrong before.

Your mileage may vary. You may decide that dairy's not worth touching with a ten-foot pole, and that's great. We applaud you, and promise not to send you emails demanding an explanation.