Few nutrition topics are in a more constant state of froth than the place of dairy in a healthful diet. And that's really saying something, because nutrition topics in general are pretty frothy.
I have made my case now, more than once, that despite our decidedly imperfect knowledge of nutrition, we do have actual knowledge of nutrition—and that it is the basis for opinions worth sharing. Knowledge and expertise should be the basis of widely disseminated opinions about nutrition, just as they are the basis for such opinions in engineering, architecture, and rocket science.
But nutrition is perennially in a second-rate henhouse, where not only are those with no particular knowledge of hens invited to stand guard and opine, but so, too, are the foxes. In the case of nutrition, that means those who have a specific food-marketing agenda are not only at liberty to disseminate views about what's good to eat, but even to design measurement scales of nutritional quality that the world seems willing to take seriously. It would be as if Dell's assessment of the new MacBook carried exactly the same weight as that of Computerworld or Consumer Reports. Really, it's that weird.
I'm not sure why it is that way—I suppose it's because everyone eats. But for whatever reason, we all wind up chewing on a lot of rather unsavory food for thought in this area. Mere opinions about nutrition are propounded as if gospel, and then milked for all they're worth in the marketing of books, lotions, potions, programs, and platforms.
Which brings us back to dairy.
A Google search of "dairy and health" today yields 139 million sites. Limit that search to news only, and you still get more than 58,000 returns. Search "milk and health" instead, and more than 300 million sites return. Plug in just "milk" and you get upwards of 500 million sites, although admittedly some of those are about Harvey Milk. But not many.
For the most part, this large, churning vat of opinion represents the selective representation of diverging scientific information about dairy intake.
From the dairy advocates, there are claims that milk and dairy intake are vital for bone health; that dairy intake is essential for strong muscles and healthy skin; that dairy defends against obesity, diabetes, heart disease, and cancer. There are claims that the calcium and vitamin D in milk do things that calcium and vitamin D supplements cannot. There are claims that the saturated fat in dairy is not harmful and may even be beneficial. There are claims, in short, that dairy is just about the best damn food there is.
But the dairy detractors—which, interestingly, include two very disparate groups, the herbivorous vegans, and the rather carnivorous Paleo dieters—spout off a panoply of countervailing claims: that dairy increases cancer risk; that dairy increases cardiovascular risk; that dairy is irrelevant to bone health, or actually detrimental; that dairy consumption is abusive to cows, and the planet; that dairy intake by adult mammals is simply…unnatural.
This last one deserves a bit of explanation. Milk contains the sugar lactose, which is comprised of pairings of glucose and galactose. To digest this sugar, we must break lactose into its component parts (lactose is too big to absorb otherwise), and that requires an enzyme: lactase. All infant mammals make lactase, but the gene that does the job shuts off in early childhood, at the time of weaning. Throughout nature and history, the only milk to which mammals had access came from their own mothers in the first months to years of life.
But in humans—and only in humans—something changed. Over the millennia since the dawn of agriculture, the ability to ingest dairy clearly conferred a selective survival advantage on older children and adults in pastoral societies that could access the milk of other species. The result is that human ethnic groups with a long tradition of pastoralism have high rates—all but universal—of lactose tolerance. In contrast, groups with no such tradition have equally high rates of lactose intolerance. This is a clear, if rare, case of natural selection in fast-forward, on vivid display within the span of recorded history.
Competing claims about dairy take us deep into the curds and whey. There are arguments that dairy is good, but only if raw; pasteurization, so goes the contention, ruins everything by destroying the active "enzymes." There are claims that skimming the fat ruins dairy by removing healthful fatty acids, such as conjugated linoleic acids, and other claims that only low-fat and non-fat dairy are good, while full-fat is bad. There are claims that all dairy is good; that milk is good but cheese is bad; that cheese is good, but milk is not; that milk and cheese are good, but butter is not.
I have done my best to keep pace with the literature on such topics, and evaluate it without bias. Honestly, I don't have a strong need to include or exclude dairy from my diet, and have always been willing to do either. I am interested in, and willing to accept, the truth— whatever it is.
So what is it?
First, I don't think the issue of dairy consumption being "unnatural" is valid. If we go back in time beyond the advent of agriculture, it's true that adult mammals consuming dairy is "unnatural." But why stop there? If we go back far enough, we were fish—and breathing air is then unnatural. Any such adventures in time travel require some arbitrary stopping point, which can result in silliness.
The simple fact is that environmental conditions and physiology change in tandem—that's what natural selection is all about. A substantial portion of the adult human population is now lactose tolerant, so dairy consumption has become natural for us. At least some of us.
Whether or not consuming dairy is good for us depends on the type of dairy in question, how much of it we're eating—and with what other foods—as well as what we're omitting to accommodate it.
Globally, there is clear evidence that dairy intake is NOT essential for the health of adult Homo sapiens. Populations that drink mostly water, eat mostly plants, exercise routinely, and get sunlight—a fast-vanishing combination, alas—tend to have strong bones and hearts and low rates of cancer, stroke, diabetes, with no thanks owed to dairy for any of it. In populations with more physical activity and more sun exposure, but less dairy intake than in the U.S., osteoporosis is less common, not more. In the U.S., where outdoor physical activity levels are low and protein intake is high, dairy is decisively associated with better bone density.
There is no clear evidence that making room for dairy has any capacity to improve the quality of diet, or health, for those cultures that drink mostly water and eat mostly plants. But in the U.S., we drink lots of soda and consume a bounty of highly processed foods. The inclusion of dairy in diets here almost certainly means less of those items, and the epidemiologic evidence shows clearly a net benefit of that shift. In the U.S., typical diets including dairy routinely are associated with better health outcomes than typical diets that exclude it.
Dairy detractors tend to promote alternatives, such as soy milk. But the evidence of health benefits from soy derive from Asian cultures consuming miso and tofu–not from Western cultures consuming soy milk and soy ice cream. We have no evidence that dairy alternatives offer health benefits over dairy.
The Dietary Approaches to Stop Hypertension (DASH) studies indicate that the inclusion of low- and non-fat dairy in the diet helps lower blood pressure. Other studies, including large meta-analyses, suggest a modest, net benefit in the areas of all-cause mortality and cardiovascular disease, and no net increase in cancers. But such studies do tend to distinguish low- and non-fat from full-fat dairy; in general, benefits seen with the fat-reduced varieties are not seen, or attenuated, with full-fat varieties.
According to my friend, author and animal-rights activist John Robbins, among others, dairy farming is never very good for the cows involved. For whatever it's worth, I have visited some local farms and spoken to family farmers who suggest it can be humane. I share John's concern that all too often it isn't.
Animal husbandry comes at an environmental cost, which is an increasingly important consideration. But the highest priority solution here would be for us to eat less meat, and mostly plants. Dairy farming can, allegedly, be fairly environmentally friendly, according to a recent article published in Slate.
Looking across an expanse of evidence without prejudice, I see a case for low-fat or non-fat, minimally processed, organic, pasteurized dairy as a beneficial element in the American diet. Making this food category a regular part of the diet offers likely health benefits when compared to a typical American diet that favors sugar-sweetened beverages and processed foods. In the context of our culture, milk can displace soda, and yogurt can displace less nutritious snacks.
There are few if any studies comparing optimal plant-based diets with and without dairy, or optimal Paleo diets with and without dairy. Such studies are not even plausible, but in their absence, we can't say that adding dairy to such diets would make them better, or worse. There is no good evidence-based case for healthy vegans to add dairy to their diets. On the other hand, I can find no good evidence that popular dairy substitutes are reliably more nutritious.
Personally, I eat food, mostly plants, and drink mostly water—but I am not a vegan. I don't go out of my way to add dairy to my diet, but I don't go out of my way to avoid it, either—and have some almost every day, just the kind I recommend above. This is about where one lands if the available nutrition science is milked for all it's worth—but not beyond.
David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.