"Alkaline Diets, Animal Protein, and Calcium 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.
So if our body isn't buffering the acid formed from our diet
with our bones, how is it neutralizing the acid?
Maybe with our muscles--alkaline diets may protect our muscle mass—
all covered in my next video,
entitled "Testing Your Diet with Pee and Purple Cabbage".
Stay tuned!