One of the most contentious issues in the Paleo nutrition community is whether dairy products are health-promoting or disease-causing.

On one end of the spectrum you have Loren Cordain and his group, who claim that dairy is not fit for human consumption for two reasons: 1) because it’s a neolithic food and not part of our evolutionary heritage, and 2) because of proposed physiological mechanisms by which dairy causes harm when consumed. On the other end of the spectrum you’ve got folks like Kurt Harris, Stephan Guyenet, Chris Masterjohn and the Weston A. Price Foundation who have pointed out the many health benefits of dairy and are generally in favor of its consumption.

My answer to the question of whether dairy is healthy are harmful is, in short: it depends. But before we get into the factors I think the answer depends on, I want to briefly address why I don’t take the evidence against dairy very seriously at this point.

Paleo re-enactment isn’t the goal

I agree with Dr. Kurt Harris on this one.

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.

There’s also the inconvenient (for the anti-dairy set) matter of people like the Masai and Loetschental Swiss that Weston A. Price studied, who were free of modern, degenerative disease despite receiving a large percentage of calories from dairy products.

Human evidence is more convincing than proposed mechanisms

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 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. Here’s what they found:

At baseline, higher circulating levels of trans-palmitoleic acid were associated with healthier levels of blood cholesterol, inflammatory markers, insulin levels, and insulin sensitivity, after adjustment for other risk factors. During follow-up, individuals with higher circulating levels of trans-palmitoleic acid had a much lower risk of developing diabetes, with about a 60% lower risk among participants in the highest quintile (fifth) of trans-palmitoleic acid levels, compared to individuals in the lowest quintile.

Translation: 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.

Since trans-palmitoleic acid is a fatty acid found in the – you guessed it – fat of milk, the study also supports the idea that full-fat, whole dairy products are beneficial. This directly contradicts the low-fat hysteria we’ve been brainwashed with for so many years. But I digress.

Stephan Guyenet blogged about this study and re-wrote the authors’ conclusion in more straightforward terms:

Our findings support eating as much butter as possible****. Don’t waste your money on low-fat cream, either (half-n-half). We’re sorry that public health authorities have spent 30 years telling you to eat low-fat dairy when most studies are actually more consistent with the idea that dairy fat reduces the risk obesity and chronic disease.

Since this was an observational study, it doesn’t prove that dairy fat reduces the risk of T2DM. But it does suggest that the converse isn’t true.

Another study found that people with the highest levels of milk fat biomarkers, suggesting they consumed the most dairy fat, were actually at lower risk of heart attack; for women, the risk was reduced by 26 percent, while for men risk was 9 percent lower.

Another study showed that people who ate the most full-fat dairy had a 69% lower risk of cardiovascular death than those who ate the least.

Finally, this literature review of 10 studies found that milk drinking is associated with a small but significant reduction in heart disease and stroke risk.

I could go on, but I think you get the point. Which is this: evidence of what happens when people actually consume dairy products is a lot more convincing to me than proposed mechanisms of how dairy may effect humans.

The problem with isolating certain effects of a nutrient or food, and then making predictions based on those effects, is that we might miss some other quality about that food that negates the proposed effect.

That’s a mouthful, so let me explain.

T. Colin Campbell is (in)famous for his research linking casein, a protein in dairy products, with cancer. He then made the huge and unsupportable leap to concluding that all animal proteins cause cancer and should be avoided. Most of you know the rest of that story.

However, what Campbell neglected to notice, or mention, is that whey, another protein found in dairy, has anti-cancer effects that completely cancel out the cancer-promoting effects of casein. Oops! This is why it’s so important to study whole foods, not just nutrients.

So let me finish this section by saying that I believe the weight of the evidence on dairy consumption suggests that it is not only not harmful, but quite beneficial.

When dairy may not be beneficial

However, as in most things, there are exceptions. Many of you reading this are probably sensitive to dairy and don’t tolerate it well. I certainly have patients that this is true for, and it’s not at all uncommon.

What’s the deal? Why does it seem to benefit some, but cause problems for others? In my opinion the answer boils down to the health of the gut. 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.

Not all milk is created equal

Something that irritates me is that raw and pasteurized dairy is often discussed as if it’s the same thing. It’s not. Raw dairy is a whole food, and pasteurized dairy is a processed food.

While it’s true that some people (described above) react to the proteins in milk, most who are sensitive are reacting to the sugar in milk: lactose. The enzyme lactase must be present to hydrolyze lactose into its constituent compounds, glucose and galactose. Somewhere between 1% – 95% of people don’t produce lactase on their own, depending on race and ethnicity.

In a sign of nature’s wisdom, raw milk contains lactase, the enzyme needed to digest lactose. Pasteurization, however, kills lactase. So if you don’t produce your own lactase, you’ll have a hard time digesting pasteurized milk. But that doesn’t mean you can’t tolerate raw milk. I can’t tolerate pasteurized dairy myself, but I don’t seem to have any problems with raw dairy.

So the answer to the question I posed in the title of this article isn’t so simple, and it depends on several factors:

The status of your gut barrier

Whether or not you have SIBO or IBS

Whether or not you’re gluten intolerant

Whether you’re eating raw or pasteurized dairy

If you’re not sure where you stand with dairy, the best approach is to remove it for 30 days and then reintroduce and see what happens. Elimination/reintroduction is still the gold-standard for determining sensitivity to a particular food.

But if you tolerate it well, I haven’t seen any evidence in the literature that convinces me you shouldn’t be eating liberal amounts of full-fat dairy.