Healthy Bones

We have a lot of choices to make about our diet. Add to that – doing the right thing when it comes to treating a chronic illness, fighting a virus, or losing weight, and suddenly, our nutrition choices can seem almost overwhelming.  

Well, I’m here to help. Welcome to the Nutrition Facts podcast. I’m your host – Dr. Michael Greger.

Today, it all comes down to the shape and support of our body, the protection of our organs – and those things – without which we would quickly become a gelatinous mass: our bones.

In our first story, we look at how those eating plant-based diets may be so slim – that they suffer from bone mass loss.

Osteoporosis is estimated to affect 200 million people worldwide. Literally meaning “porous bone”, osteo-porosis is a disease characterized by reduced bone formation, excessive bone loss, or a combination of both, leading to bone fragility and an increased risk of fractures. And bone mineral density is the most robust and consistent predictor of osteoporotic fracture. What can we eat to boost our bone density? Well, we know that increased consumption of plant foods is associated with increased bone mineral density.

There’s an extensive range of micronutrients and phytochemicals packaged within plants that can be powerful promoters of bone health. So, healthcare professionals should be encouraged to advise the increased consumption of plant-based foods, particularly in mid-life, irrespective of the clients’ underlying dietary pattern––meaning no matter how much meat or junk they eat, adding more healthy plant foods may help prevent the development of osteoporosis.

On the other hand, a more animal-source nutrient pattern has been associated with a higher risk of fractures, suggesting that a more animal-based diet is related to bone fragility. So, one would expect less osteoporosis in those eating plant-based diets. But you don’t know, until you put it to the test.

The “Incidence of Osteoporosis in Vegetarians and Omnivores”, the first study, published nearly 50 years ago, and…the density of the bones that were measured was significantly greater in the vegetarians than in the omnivores. In fact, the average bone densities of the vegetarians in their 70s was greater than the densities of the meat-eaters in their 50s. Bottom line, these results suggest that there is less likelihood of vegetarians developing osteoporosis in old age.

Turns out, though, that the researchers screwed up. DEXA scanning, which is what we use now, didn’t come online until the 1980s. So, the researchers were just using regular x-rays, and they confused the readings, such that darker bones on x-rays got a higher score. But, that actually means less bone; so, their conclusion should have been the opposite of what they claimed. So, vegetarians had worse bone mineral density.

Fast forward about 40 years, by which time nine studies had been done on thousands of individuals. And all in all, the results suggest that vegetarian diets—particularly vegan diets––are associated with lower bone mineral density. But, the magnitude of the association is clinically insignificant, meaning the difference was so small as to not really matter out in the real world, reinforcing the fact that vegetarian diets have no clinically detrimental effect on bone health.

And, it is important to note that the findings of lower bone mineral density didn’t fully control for key confounding factors, such as for differences in body weight. We know that people who are obese have stronger bones. Why? Because they’re weight-lifting 50 pounds all day every day. Maybe 100 pounds. If you walked around with a 100-pound backpack every day, your bones would grow stronger, too. That’s how you build strong bones: weight-bearing exercise. So, people who weigh more have denser bones. And vegetarians, and especially vegans, have such low rates of obesity that no wonder, on average, they would have lower bone density. They didn’t take weight into account, but if the difference they found isn’t even clinically significant, who cares? As of 2009, the answer to the question, “Is vegetarianism a serious risk factor for osteoporotic fracture?” The answer was no. Vegetarianism is not a serious risk factor.

By 2018, the latest meta-analysis on veganism, vegetarianism, and bone mineral density, we were up to 20 studies, involving tens of thousands of participants, and…, lower bone mineral density was found in studies of vegetarians and vegans compared to meat-eaters. The researchers conclude that vegetarian and vegan diets need to be appropriately planned to preserve their bones. But wait, did they account for the obesity thing?

No, they did not. They just used what are called crude risk ratios, meaning no adjustments for confounding factors like weight. So, they didn’t control for things like age, smoking, obesity, exercise, and so their results are really uninterpretable. But no one had gone through the trouble of going back through all those studies and making the proper adjustments, until now.

The title gives it away: “Differences in Bone Mineral Density between Vegetarians and Nonvegetarians Become Marginal when Accounting for Differences in Body Size Factors.” Yes, bone mineral density values were significantly lower among vegetarians than among nonvegetarians, just like is the case with nearly every study on bone mineral density and excess body weight. But forget clinical significance; these differences even lost statistical significance upon adjustment for body size factors, suggesting that lower bone mass among vegetarians is in larger parts explained by their lower BMI and waist circumference. Thus, it’s not so much the composition of the diets of vegetarians and vegans as much as it is the fact that they become so much slimmer.

Now, a small but statistically significant difference remained for total lower spine density––a difference of 0.03. This was dismissed as having little clinical relevance, but is that true? If you look at the reproducibility of bone mineral density measurements in daily medical practice, you can see, if you repeat tests back to back, there’s some scatter in the measurements. And so, a significant difference really has to be more than the inherent variation, and indeed, expressed as the smallest detected difference, you really need a BMD disparity of at least 0.05 at the spine before it can be considered a significant change. And so indeed, there does appear to be little clinical relevance. However, even if vegetarians and vegans basically have the same bone density at the same weight, everyone who is skinny is at risk. Low BMI is a risk factor for fractures; so, all persons in a low body weight category consuming any kind of diet should be monitored for osteoporosis.

In our next story, we look at the decades-old dogma that animal protein leads to bone loss.

For most of the last century, a prevailing theory within the field of nutrition was that by eating acid-forming foods (such as meat), we were, in essence, at risk of peeing our bones down the toilet. And, no wonder! Experiments dating back to 1920 showed over and over that if you add meat to the diet, you get a big spike in the amount of calcium being lost in the urine. And so, this made total sense; we had known since 1912 that meat was acid-forming within the body. And, how do you buffer acid? What are in antacid pills, anti-acid pills—like Tums? Calcium.

Meat and eggs have a lot of sulphur-containing amino acids (two to five times more than grains and beans) that are metabolized into sulphuric acid, which the body buffers with calcium. That’s why the antacids, like Tums, are made out of calcium. Calcium can buffer acid. And, where is calcium stored in the body? The skeleton. So, the thinking was that every time we ate a steak, our body would pull calcium from our bones, bit by bit, and over time, this could lead to osteoporosis. Based on 26 such studies, for every 40 grams of protein we add to our daily diet, we pee out an extra 50mg of calcium. And look, we only have about two pounds of calcium in our skeleton; so, the loss of 50 a day would mean losing close to 2% of our bone calcium every year. And so, by the end of the 20th century, there was little doubt that acid-forming diets would dissolve our bones away.

But, if you actually look at all the studies done on protein intake and bone health, that’s not what you find. So, where’s the flaw in our logic? Meat leads to acid, which leads to calcium loss, which leads to bone loss, right?

Well, it’s uncontroversial that protein results in greater calcium excretion, but we’ve just been assuming it’s coming from the bone. I mean, where else could the extra calcium dumped in our urine be coming from, but from our bones?

This is the study that appeared to solve the mystery. An intrepid group of researchers tried feeding a bunch of volunteers radioactive calcium, and then putting them on a high-protein diet. What happens when you put people on a high-protein diet? The amount of calcium in their urine shoots up. And indeed, that’s just what happened. But, here’s the big question: was that extra calcium in their urine radioactive, or not? And, to everyone’s surprise, it was radioactive—meaning that the excess calcium in their urine was coming from their diet. Remember, they were feeding them radioactive calcium. So, the excess calcium in their urine wasn’t coming from their bones, but from what they were eating.

What seemed to be happening is that the excess protein consumption boosted calcium absorption—from down around 19% up to 26%. So, all of a sudden, there was all this extra calcium in the blood, so presumably the kidneys are like, whoa, what are we going to do with it all? So, they dump it into the urine. 90% of the extra calcium in the urine after eating a steak doesn’t appear to be coming from our bones, but from our diet. We’re not sure why protein boosts calcium absorption. Maybe the protein increases the solubility of calcium by stimulating stomach acid production? Whatever the reason, yes; more calcium lost. But, more calcium gained, such that in the end, most of that extra calcium is accounted for. So, in effect, more calcium is lost in the urine stream, but may be compensated by less loss of calcium through the fecal stream.

This was repeated with even more extreme diets— an acid-forming five burgers a day worth of animal-protein diet that limited fruits and vegetables, versus an alkaline diet emphasizing fruits and vegetables. More calcium in the urine on burgers, but significantly greater calcium absorption, such that at the end, it was pretty much a wash.

Other studies have also since supported this interpretation. Here’s an ingenious one. Feed people a high animal-protein diet, but with “an alkali salt to neutralize the acid.” Now, the old thinking would predict that there would be no calcium loss, since there was no excess acid to buffer. But no, even though the acid load was neutralized, there was still [this] excess urinary calcium, consistent with the radioactive isotope study, “challenging the long-standing dogma that animal protein consumption results in an acidosis that promotes the [excess] excretion of calcium…”

Finally today, we look at how the galactose in milk may explain why milk consumption is associated with significantly higher risk of hip fractures, cancer, and premature death.

Milk is touted to build strong bones, but a compilation of all the best studies found no association between milk consumption and hip fracture risk; so, drinking milk as an adult might not help bones. But what about in adolescence? Harvard researchers decided to put it to the test.

Studies have shown that greater milk consumption during childhood and adolescence contributes to peak bone mass, and is therefore expected to help avoid osteoporosis and bone fractures in later life. But that’s not what they found. Milk consumption during teenage years was not associated with a lower risk of hip fracture, and, if anything, milk consumption was associated with a borderline increase in fracture risk in men.

It appears that the extra boost in total body bone mineral density you get from getting extra calcium is lost within a few years, even if you keep the calcium supplementation up. This suggests a partial explanation for the long-standing enigma that hip fracture rates are highest in populations with the greatest milk consumption. Maybe an explanation why they’re not lower, but why would they be higher?

This enigma irked a Swedish research team, puzzled because studies again and again had shown a tendency of a higher risk of fracture with a higher intake of milk. Well, there is a rare birth defect called galactosemia, where babies are born without the enzymes needed to detoxify the galactose found in milk; so, they end up with elevated levels of galactose in their blood, which can cause bone loss even as kids. So maybe, the Swedish researchers figured, even in normal people who can detoxify the stuff, it might not be good for the bones to be drinking it every day. And galactose doesn’t just hurt the bones. That’s what scientists use to cause premature aging in lab animals They slip them a little galactose and you can shorten their lifespan, cause oxidative stress, inflammation, brain degeneration, just with the equivalent of one to two glasses of milk’s worth of galactose a day. We’re not rats, though—but given the high amount of galactose in milk, recommendations to increase milk intake for prevention of fractures could be a conceivable contradiction. So, they decided to put it to the test, looking at milk intake and mortality, as well as fracture risk, to test their theory.

A hundred thousand men and women followed for up to 20 years; what did they find? Milk-drinking women had higher rates of death, more heart disease, and significantly more cancer for each glass of milk. Three glasses a day was associated with nearly twice the risk of death. And they had significantly more bone and hip fractures, too.

Men in a separate study also had a higher rate of death with higher milk consumption, but at least they didn’t have higher fracture rates. So, a dose-dependent higher rate of both mortality and fracture in women, and a higher rate of mortality in men with milk intake, but the opposite for other dairy products like soured milk and yogurt, which would go along with the galactose theory, since bacteria can ferment away some of the lactose. To prove it though, we need a randomized controlled trial to examine the effect of milk intake on mortality and fractures. As the accompanying editorial pointed out, we better figure this out soon, as milk consumption is on the rise around the world.

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