Add to that, doing the right thing

when it comes to preventing

and treating a chronic disease,

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 a loss of bone mass.

Osteoporosis is estimated to affect 200 million people worldwide.

Literally meaning "porous bone ," osteoporosis is a disease

characterized by reduced bone formation, excessive bone loss,

or a combination of both, leading to bone fragility

and 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 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 there's 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 the x-ray

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, and 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.

The researchers 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, was up to 20 studies,

involving tens of thousands of participants, and, again,

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 how

if you do 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 bone mineral density 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 the lack of 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 sulfur-containing amino acids,

2-5 times more than grains and beans

that are metabolized into sulfuric 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 every 40 grams of protein

we add to your daily diet we pee out an extra 50mg of calcium.

And look we only have about 2 pounds of calcium in our skeleton,

so the loss of 50 a day would mean

losing close to 2% of 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

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 in 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.

The old thinking would predict that there

would be no calcium loss since there is no excess acid to buffer.

But no! Even though the acid load was neutralized

there was still the excess urinary calcium,

consistent with the radioactive isotope study,

challenging this 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

has been 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?