Animal
Health
Protein
and
Bone
Does animal protein in our diet result in higher risk of
bone fractures and osteoporosis? It appears so. A broad
array of clinical epidemiological studies has found a
strong, positive association between animal protein intake
and risk of bone fractures. The protein causes acidosis in
our bodies when we metabolize it, and one of the mechanisms
used to neutralize that acidity appears to be leaching
calcium from our bones.
Transcript
Sources
Credits
Video Transcript:
Harvard’s School of Public Health explains very nicely the
mechanism by which protein can cause problems for bone health.
It says, “as your body digests protein, it releases acids into
the bloodstream, which the body neutralizes by drawing calcium
from the bones. Following a high-protein diet for a few weeks
probably won’t have much effect on bone strength. Doing it for
a long time, though, could weaken bone.”
Now we’ve known for a very long time that meats, including
fish, are acid forming in our body. Scientists from Columbia
University, back in 1912, analyzed acid and base forming
elements in food, and noted that, “all the meats (including
fish)…show a decided excess of acid-forming elements”; all the
“meats (including fish) show [a] decided predominance of acidforming elements.”
Back in 1920, Columbia’s Department of Chemistry also reported
that adding meat to one’s diet results in increase of calcium
loss in urine, thought to be because “the added meat gave to
the diet as a whole an excess of acid-forming over baseforming mineral elements[.]”
And what have we seen from the results of the consumption of
animal protein with regards to bones? Researchers from Yale
University’s School of Medicine looked back across a broad
array of thirty-four prior published studies across sixteen
countries, and they found these studies over time showed “a
strong, positive association” between dietary animal protein
and female bone fracture rates.
So, we’ve known for some time that this association exists. We
know eating a diet high in animal protein results in acidity,
and that our body leaches calcium from our bones to buffer the
acid. One of the mechanisms behind this phenomenon is that
animal protein has a higher amount of sulfur-containing amino
acids, and the “sulfur-containing amino acids from animal
protein lower blood pH”.
So animal proteins — including meat, fish, dairy, poultry or
eggs — have higher amounts of sulfur-containing amino acids
than plant foods. As a result, when we eat diets high in
animal proteins, our body produces sulfuric acid, which
increases the acidity in our bodies. One of the body’s
mechanisms to neutralize this acidity is to draw calcium from
our bones (similar, for example, to when we take antacids that
are made with calcium to neutralize the acidity in our stomach
associated with heartburn). The problem is that constantly
leaching calcium from our bones can reduce bone mass, making
our bones weak and more prone to fractures and osteoporosis.
Moreover, the chronically higher calcium excreted in our urine
can also lead to the development of kidney stones.
This Harvard study published in the American Journal of
Epidemiology followed over 80,000 women over twelve years, and
found that animal protein was associated with increased risk
of forearm fracture, but no increase in risk was observed with
higher intakes of vegetable protein. It found that women who
consumed the largest amount of animal protein in the study had
a 22% higher risk of fracture. Evidence suggests that “higher
protein intakes in young…women have a negative impact on
radial bone measurements”, meaning that women who consumed
higher protein diets have been found to lose bone mineral
content and bone density.
So we know that our body uses base stores (including calcium
from our bones) to neutralize the acidity we get from our
diet. This article from The Journal of Nutrition explains the
same thing. It says, “diets that are net acid producing…induce
and sustain increased acidity of [our] body fluid. With
increasing age, the kidney’s ability to excrete daily net acid
loads declines, invoking increased…utilization of base stores
([from our] bone [and] skeletal muscle) on a daily basis to
mitigate the otherwise increasing baseline metabolic acidosis,
which results in increased calciuria and net losses of body
calcium. Those effects of net acid production and its
attendant increased body fluid acidity may contribute
to…osteoporosis[.]” What this is saying is the neutralizing
mechanism in our bodies of taking calcium from our bones to
deal with the higher acidity caused by our diet can contribute
to osteoporosis.
This journal review in The European Society for Clinical
Nutrition and Metabolism further discusses the issue, noting
how problems associated with acidity become even worse with
age. “The modern Western-type diet…contains excessive animal
products, generating a state of metabolic acidosis, whose
magnitude increases progressively with aging due to the
physiological decline in kidney function.”
As explained in this peer-reviewed study from the Journal of
Nutrition, “The average American diet, which is high in
protein and low in fruits and vegetables, generates a large
amount of acid, mainly as sulfates and phosphates. The kidneys
respond to this dietary acid challenge with net acid
excretion, [and] the skeleton supplies buffer by active
resorption of bone.” The study concludes, that, “Overall, the
evidence leaves little doubt that excess acidity will create a
reduction in total bone substance…. An acid-ash diet [means] a
diet that creates acid in the process of its metabolism[,]”
and this article concludes, “[m]odern peoples are now eating
high protein, acid-ash diets and [are] losing their bones.”
This study, published in the official journal of the Council
on Renal Nutrition of the National Kidney Foundation and the
International Society of Renal Nutrition and Metabolism,
compared the net acid secretions among vegans (who eat no
animal products), lacto-ovo vegetarians (who eat no meat, but
do eat dairy and eggs) and omnivores (who eat a traditional
Western diet of meat, dairy and eggs). The study found that
net acid secretion was higher in both lacto-ovo vegetarians
and omnivores than in vegans, suggesting “that higher protein
intake results in more renal net acid excretion and more
acidic urine.” In addition to increased incidents of kidney
stone development, higher protein intake was also found to be
associated with “increased urinary calcium excretion.” It
noted, “higher protein intake, especially animal protein, was
linked to an increased rate of bone loss and increased risk of
hip and forearm fractures in women.” The study concludes,
“Because acid-base balance has significant implications for
renal and bone health, it is important…to introduce
appropriate dietary modifications to prevent or treat the
conditions, including kidney stones, bone loss and/or [bone]
fractures, and possibly osteoporosis.”
So to recap, eating animal proteins increases body acidity,
and one of the body’s mechanisms to neutralize this acidity is
to leach calcium from the bones. Doing this for a long time
can lead to loss of bone mass and weakened bone, increased
risk of fractures and osteoporosis, as well as kidney (or
renal) stones. And, an easy way to avoid the increased risk of
these problems is avoiding animal protein.
This transcript is an approximation of the audio in above
video. To hear the audio and see the accompanying visuals,
please play the video.
Video Sources:
• Harvard T.H. Chan, School of Public Health: Calcium and
Milk: What’s Best for Your Bones and Health? Available here
(accessed Feb. 11, 2016).
• HC Sherman and AO Gettler. The Balance of Acid-Forming and
Base-Forming Elements in Foods, and its Relation to Ammonia
Metabolism. J. Biol. Chem. 1912 11: 323-338. Available here
(accessed Feb. 11, 2016).
• HC Sherman, AR Rose and MS Rose. Calcium Requirement of
Maintenance in Man. J. Biol. Chem. 1920 44: 21-27. Available
here (accessed Feb. 11, 2016).
• BJ Abelow, TR Holford and KL Insogna. Cross-cultural
Association between Dietary Animal Protein and Hip Fracture: A
hypothesis. Calcif Tissue Int. 1992 Jan; 50(1):14-8. Available
here (accessed Feb. 11, 2016).
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Relation to Prostate Cancer: A hypothesis. Cancer Causes
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• D Feskanich, WC Willett, MJ Stampfer and GA Colditz. Protein
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Adverse Effects of Sodium Chloride on Bone in the Aging Human
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• LM Ausman, LM Oliver, BR Goldin, MN Woods, SL Gorbach and JT
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Feb. 11, 2016).
Video Credits:
This presentation was written and narrated by Sofia Pineda
Ochoa, MD, and edited by Bob Rapfogel.
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