I do a lot of myth-busting around here, and it’s usually conventional wisdom that crumbles in the face of scientific evidence. But this time I’m actually siding with conventional wisdom, and busting a myth that’s common in the alternative health community. I addressed this topic in-depth on a recent podcast, but it’s such a common question that I decided to write an article on it for easy reference.
The myth in question is the idea that dairy foods contribute to osteoporosis by ‘acidifying’ our bodies. This claim is especially common in vegan-oriented alternative health media, but also comes up in other internet realms, including those with a Paleo orientation. The claim is based on the “acid-ash hypothesis of osteoporosis,” which I addressed extensively in my ‘Acid-Alkaline Myth’ series a couple months ago. (Check out part two as well.)
For those who missed the articles, this hypothesis states that foods high in phosphate leave an ‘acid ash’ after digestion, thereby lowering serum pH. The body supposedly compensates for this and restores normal blood pH by stealing alkaline minerals (such as calcium) from the bones, thus decreasing bone density.
Because of their phosphate content, milk and other dairy products are usually considered ‘acid-producing’ foods under this hypothesis. Thus, proponents claim that even though dairy contains calcium and other nutrients that can be used to build bone, dairy’s acidifying effect on the body outweighs its calcium content and results in a net loss of bone density.
Although I’ve already written about the hypothesis as a whole, I want to specifically address the claims regarding dairy for a few reasons. First, because my readership is acutely aware of how many times conventional wisdom has led us astray, I think we’re all more likely to believe a hypothesis that directly opposes mainstream health claims. In this case, dairy is so heavily advertised as a panacea for healthy bones that it would seem only natural for those claims to be dead wrong. You’ll see that (for once) this is not the case!
Additionally, I came across a 2011 study that specifically addresses the dairy-acid balance-osteoporosis connection. They came to some interesting conclusions that I want to share with you all, and hopefully we can put this issue to rest.
Dairy, acid balance, and osteoporosis: the real scoop
In this study, “Milk and acid-base balance: proposed hypothesis vs. scientific evidence,” the authors review both the acid-ash hypothesis as a whole and the specific claim that dairy contributes to osteoporosis. After reviewing the scientific evidence (or lack thereof), they reach the same conclusions that I have: the studies available simply do not support this hypothesis.
First, they emphasize that urine pH is not indicative of systemic pH. In fact, except in cases of serious renal insufficiency, diet does not affect serum pH at all. If it did, we’d be in a lot of trouble! The pH of our blood is maintained in a very tight range, and if it deviates significantly, we will die very quickly. No doubt we can really mess up our health by eating the wrong things, but thankfully our minute-to-minute survival doesn’t hinge on whether we can correctly balance the acidity or alkalinity of the foods we eat.
Further, the bones don’t even come into play in the regulation of our serum pH; that’s our kidneys’ job. Any ‘acid ash’ that is left behind by the foods we eat can be easily dealt with and eliminated in the urine. This is why your urine changes pH depending on what you eat. It’s just a sign that your kidneys are doing their job!
In short, their conclusions simply reiterate the points I made in my Acid-Alkaline series, and demonstrate that the acid-ash hypothesis of osteoporosis has no scientific backing. But perhaps the most interesting thing about this particular study on milk is the authors’ assertion that dairy isn’t even acid-forming in the first place!
The authors cite two studies that indicate that milk actually leaves an alkaline ash as opposed to an acid ash, based on measurements of urine pH and net acid excretion (NAE) following milk ingestion in clinical trials. (Remember, this doesn’t mean that milk raises serum pH. Foods can change urine pH, but not blood pH!) So not only is the hypothesis itself wrong; the application of the hypothesis is wrong too, at least in the case of dairy. Even if the acid ash hypothesis of osteoporosis were viable, there would still be no mechanism by which dairy would contribute to osteoporosis.
Dairy probably is good for your bones after all
The majority of the evidence indicates that conventional wisdom may actually be right about dairy. Clinical studies have found that drinking milk leads to a positive calcium balance, indicating that more calcium was absorbed than was excreted. (1) Other studies show that phosphate in general – not just from milk – increases calcium retention and improves bone health. (2) Increased dairy consumption is also consistently associated with lower rates of osteoporosis and better bone health. We all know to take observational studies with a grain of salt, but when clinical data backs up their conclusions, they’re significantly more convincing.
For example, an increased dairy intake in postmenopausal Korean women was associated with a decreased risk for osteoporosis. (3) Another study found that in the US, dairy intake was a significant predictor of osteoporosis among postmenopausal women. (4) And in Polish women, higher dairy consumption during childhood and adolescence predicted better bone health as adults. (5)
Although you won’t see me sporting a milk mustache in a “Got Milk?” ad anytime soon, it does appear that dairy can be beneficial for bone health. That’s not to say it’s necessary; after all, we got along just fine without dairy for most of human history! But based on the evidence, it’s safe to say that dairy does not contribute to osteoporosis, and full-fat dairy (preferably raw) can be a beneficial addition to the diet for many people.