Is Excess Protein Harmful?
The average US diet already exceeds protein requirements, but some segments of the population, like athletes and weight-loss dieters, often have much higher …
The average US diet exceeds protein requirements
and provides about 1.2 daily grams of proteins
per kilogram of body weight.
When we refer to high protein diets, however,
we do not refer to the slightly higher protein
intake that all of us more or less have.
We refer to way higher protein intakes, over
2 grams of proteins per kilogram per day,
often 3 grams and even 4 grams of daily proteins
per kilogram of body weight.
There are mainly two segments of the population
that may have such high protein intakes.
One is weight loss dieters.
Many popular weight loss diets are high protein
These diets make you lose weight fast, although
most of the initial weight loss is not fat,
but water, to flush out the extra nitrogen.
The other segment is athletes and especially
We already know that you need a little bit
more protein to build new muscle, but the
protein you get from an average diet is in
general already more than enough.
There is a physiological limit to how much
muscle you can build in a day, and to cover
that, 10 to 20 extra grams of daily protein
will be enough even for the most motivated
of the body builders.
The DRI say that “no additional dietary
protein is suggested for healthy adults undertaking
resistance or endurance exercise”, so their
need for protein is the same as every other
Other institutions agree that athletes need
more protein, some say 0.9 grams per kilo,
some 1.2 grams per kilo, some 1.5 grams per
But anything above that, is wasted.
So when we get all that extra protein, what
do we really do with it?
We know that our body cannot store excess
protein for later use, so one of these two
things will happen.
If we need energy, then we will use the extra
protein for energy production.
And this is the case of athletes on high-protein
diets, they get all this extra proteins, they
need a tiny little bit for muscle growth,
and the rest, they just end up using it for
The other possibility, if we do NOT need extra
energy because we are sedentary, then we will
have nothing else to do with these proteins
other than converting them to fat and store
them in our adipose tissue.
This is what often happens to athletes when
for one reason or another they stop exercising,
but they keep eating the same way they were
eating before, and so all the excess protein
that before they were burning, now just get
converted to fat which will show up in their
bellies within a couple of months.
Many of them will blame the lack of exercise,
but really, the problem is not just that they
stopped exercising, but that they kept eating
AS IF they were still exercising, and now
all those extra proteins they are not burning
Our next question is, is there any particular
concern with high protein diets?
We already know that going on high protein
diets is mostly useless, but is it harmful?
One concern that is very often brought up
is that excess protein overburdens the liver
and kidneys because of the work they have
to do to catabolize them.
The liver has to remove the toxic ammonia,
turn it to urea, and send it to the kidneys
for prompt clearance.
Early nutrition scientists concluded from
this biochemical fact that somehow your liver
and kidney get tired or even damaged from
doing this extra work over the long term.
But the truth of the matter is they don’t,
we have studies done with athletes eating
insanely high amounts of proteins for extended
periods of time, and their liver and kidneys
don’t really care.
Our liver and kidneys are perfectly equipped
to deal with protein catabolism without any
problem, as long as they are healthy.
If they are not, so if you have liver disease
or kidney disease, then protein intake needs
to be more controlled.
Another possible concern is simply that you
may be getting excess calories.
Like we said, if we get extra proteins and
we don’t need them for anything else, we
will just turn them to fat and accumulate
into our adipose tissue.
But it is not a concern for athletes, since
they are burning their proteins for energy,
and while they get more calories from proteins,
they generally get less from fats and carbs.
It may be a problem of excess animal products.
For most people, going on a high protein diet
generally means just eating more meat and
animal products which is bad, not for the
proteins but for everything else, you’re
likely getting a lot of saturated fat, have
a diet that’s low in fiber, your gut microbiota
will change in a way that’s less favorable,
increasing the risk for colon cancer, and
Again, this is not generally a problem for
athletes since they mostly use isolated proteins,
the typical protein shake.
But for normal people, going on a high protein
diet, they’ll just eat a lot of animal food.
Dehydration is another possible concern, remember
that high proteins induce water loss, so if
you are not drinking enough, that may become
It is however a minor concern, since generally
we drink enough water.
The most significant concern associated with
high protein diets is that they increase urinary
excretion of calcium.
When you go on a high protein diet you start
flushing out a lot of calcium, and we are
not exactly sure why this happens, but very
likely it is because to catabolize amino acids
and especially the sulfur containing ones,
methionine and cysteine, we generate acids
that need to be buffered to maintain the right
The kidneys normally do that, but if we have
a lot then the kidneys alone can’t do it,
and so we use calcium to buffer these acids,
make salts and flush them out.
The first consequence of this is an increased
risk for kidney stones formation, although
this only happens in genetically predisposed
The other concern is bone mineral loss and
risk of osteoporosis and bone fractures.
Indeed, if we are not getting enough of this
calcium from diet, we will need to steal it
from our bones to buffer the protein-generated
And if this happens over and over again, we’ll
deplete our bones of their precious calcium.
Once again, for athletes this is a minor concern,
because resistance training is so good at
increasing bone strength that it more than
compensates any possible issue with calcium.
So in conclusion, exceeding protein needs
is unnecessary because we already get enough
from our normal diet, but for athletes it
is not a major concern, they’ll just use
the excess protein for energy.
However, for sedentary individuals long term
excess protein can be detrimental: it’s
a lot of excess calories, it’s a lot of
animal products, and it will increase calcium
excretion and therefore risk of kidney stones
and loss of bone mineral density.
On top of their function as a part of proteins,
individual amino acids may directly intervene
in some metabolic pathways on their own or
as starting material to build other important
non-protein regulatory molecules.
For example, the amino acid tryptophan is
precursor of the vitamin niacin and of the
neurotransmitter serotonin, and for this reason
it has been marketed as an individual supplement
for pain, depression, or insomnia.
The amino acid tyrosine is the precursor of
neurotransmitters dopamine, adrenaline and
noradrenaline, as well as the skin pigment
melanin, and the thyroid hormone thyroxine
together with iodine.
Glutamate is used to build the neurotransmitter
gamma-aminobutirrate (GABA), by decarboxylation.
Cysteine is used to make taurine, essential
for bile acids metabolism, muscle functioning
and many more.
Lysine and methionine are used to make carnitine,
to transport fatty acids across mitochondrial
The branched chain amino acids, leucine, isoleucine
and valine, are so named because they have
a branched carbon skeleton.
These are the three amino acids that are preferentially
used by our muscle as energy source when glycogen
stores are depleted.
For this reason they are often sold as supplements
and marketed as “amino acids for sport”,
but you’ll likely not need them because
you get enough from food.
They are also abundant in milk whey.
Arginine, glycine and methionine are needed
to build creatine, a quick backup source of
energy in our cells.
Arginine is also a precursor of nitric oxide,
which has a vasorelaxant effect on our blood
vessels thus lowering blood pressure and improving
For this reason it is often marketed as a
sport supplement, as well as glutamine, which
appears to immune immune function but also
preserve lean body mass and promote muscle
On top of the twenty amino acids used for
protein synthesis, there are a few other that
our body needs to regulate specific metabolic
pathways, such as ornithine and citrulline
in the urea cycle.
Although some amino acids are sold individually
as supplements, research is often limited
and we need to be careful not to confuse single
supplements with the therapeutic value of
Single amino acid supplements are almost always
dangerous if used improperly.
The biggest problem with single amino acids,
aside from the fact that they are very expensive
and their taste is horrible, is that they
may alter absorptive mechanisms in the intestine.
Amino acids often share the same carriers
for absorption, as if they all had to all
go through the same door to be absorbed.
If you have large excess of just one or a
few, chances are that the other will not be
They will be lost among this excess of one
single amino acid, and so absorption of all
the remaining essential amino acids may be