Optimum protein intake
Daily requirement -
Indispensable amino acids -
PDCAAS - Optimum
dietary excess has adverse health consequences, and proteins are no exception.
Since the body cannot store proteins, any excess is broken down in the liver and eliminated
through the kidneys. Thus, excess protein elimination puts
additional burden on the
possibly causing organ damage in the long run. The
kidneys being miraculously efficient, even significant reduction in their capacity
wouldn't cause noticeable health effect in most people. However, for those less
fortunate, with less than healthy kidneys, it can make a difference between
getting by fine, and having serious health problems.
The increased rate of fluid output reduces the time that the kidneys
have to reabsorb the minerals, which are consequently lost with the
fluid at a higher rate. More so, if calcium plasma levels are elevated
to buffer acidifying effect of high-protein diet. It was long though
that loss of calcium due to high-protein intake promotes bone loss (osteoporosis).
According to the long-term study of The American Journal of
Clinical Nutrition, even moderately elevated protein intake of 75g per day, with daily
calcium intake as high as 1400mg, already results in
more calcium lost than
Some recent studies, however, indicate that urinary loss of calcium due
to higher protein intake is offset by better absorption rate. But
these studies do not address long term effects, nor how this may vary
individually in the population at large.
In addition to possible negative effect on body calcium level, there is a
number of undesirable metabolic
consequences of high-protein diet.
Excess amino acids, as most other nutrients, can also have toxic
effect, but only if taken in supplemental form in very large doses, or
in large quantities for prolonged periods of time. Some amino acids can cause complications in
pregnancy; some can negatively interfere with MAO drugs.
Excessive dietary intake of proteins can negatively affect body's ability
to use other nutrients, and cause deficiencies (for instance, calcium, iron - from
excessive soy or dairy protein18
- or vitamin B67).
The level of protein intake at which it becomes excessive is somewhat
arbitrary, and varies individually. In general, excessive intake
probably begins at about 20% of total calories from proteins, somewhat less toward
the higher end of caloric intake range, and
somewhat more toward the lower end.
Individual cases of protein deficiency
in adults are very rare in developed countries (read: in the absence of
starvation) except for those at highly restricted caloric intake and,
probably, for older folks. Some studies indicate
that 0.8g/kg/day protein intake may not be generally sufficient to
satisfy protein needs of the elderly, most likely due to proteins being
utilized less efficiently.
Along these lines, safe protein intake does not necessarily guarantee your
body is getting all the protein it needs. While unlikely, deficiency is still possible
and, in its origin, not
likely to be protein-intake-related. It can be caused by faulty digestion, absorption
and/or assimilation (low stomach acid and/or pancreatic
enzymes, malabsorption, deficiency in nutrients needed to metabolize
Thus correcting these problems also corrects amino
acid deficiency. Otherwise, you may get into unhealthy vicious circle of
craving (even more) protein-rich foods, resulting in unbalanced, poor
diet, while what your body really needs are nutrients needed to
efficiently digest and metabolize already available proteins.
Another possible protein deficiency scenario is when your
individual needs are increased by an extended physical or
psychological trauma - regular intense physical activity
resulting in a significant build up of a muscle mass,
significant toxic exposure, or stress level, all fall into this
category - and:
(1) your protein intake is marginal,
protein absorption/assimilation is compromised, and
Possible extent and consequences of such multitude of negative factors
were not specifically addressed when the needs
"normal healthy subjects"
have been established.
Metabolic inefficiency in the digestion of proteins can be caused by
low gastric acid,
likely to inhibit action of pepsin (digestive enzyme). Both are needed
for the initial break down of proteins into peptide forms. Low gastric acid can be
result of the overuse of antacids, mineral imbalance (too much
genetic glitch, toxic exposure, or simply aging.
Absorption of proteins into bloodstream can be inefficient due to low production of
enzymes needed to break proteins down to
amino acids), by the pancreas. And it can be made sluggish by a
number of factors: excessive alcohol, or sugar intake, excessive
intake of processed foods, poor in enzymes and
stress, especially when compounded with the lack of
Another possible protein absorption bottleneck is
inflamed gut lining,
due to anything from genetically based or acquired food sensitivities, to junk
food diet, overuse of antibiotics and prolonged stress, all usually
complicated with intestinal dysbiosis (over-multiplying of bad,
bacteria), and leaky gut.
Yet another is in the
assimilation of amino
acids at the cellular level, due to cellular membranes
damaged by trans-fatty acids and/or free radicals - both
promoted by nutritionally poor diets of junk, over-processed foods,
low in antioxidants and commonly containing
chemical substances -
or some other malfunction related to transport of amino acids across
the cellular membrane.
One has to allow for the possibility that there could be a significant difference between
the level of protein ingested, and that of amino acids reaching
their final destination - the cytoplasm of your body cells. While most people don't
need to worry about sufficient dietary intake of proteins, checking
on your actual protein absorption/assimilation level with
lab tests may
be a good thing to do in any serious, chronic health condition.
Optimum protein intake
Much of publicly circulating information related to dietary protein
and its health significance results from lobbying of the
powerful meat and dairy industries. It perpetuates the hype that
one needs to consume significant proportion of high-protein foods in
order to maintain optimum health.
The fact is that, around the world, native groups
of people with the highest life expectancy and lowest disease rates all have
diets with moderate to low - down to ~50g a day - protein intake, mostly from plant
sources (which may have generally better rate of utilization by the body).
This intake level is also close to the estimated minimum safe level of
protein consumption of 0.75g/kg/day.
On the other hand, Eskimos, who consume as much as 250g-400g of animal proteins
a day, have low life expectancy and often very high rates of osteoporosis.
a strong real-life indication that
moderation in protein
consumption supports optimum health,
as opposed to protein excess. Not surprising,
mind you, since this is rather a general rule.
But we can't directly compare humans leaving in different conditions. Protein needs - as well as those
for most other nutrients - are likely to be higher for us, living in much
more polluted and stressful environment of the modern world, than for
native people in near-pristine environments.
Specific figure is necessarily
speculative to some degree and, as always, reflecting broad average - but the overall set of known factors seems to be
indicating that the optimum average
protein intake in developed countries shouldn't be lower than ~1g/kg/day.
is always the level after which protein intake becomes
unhealthy. That level, for adults - with the possible exception of the
elderly, or individuals with impaired protein absorption/utilization - seems to be
placed above ~1.5g per
kg of body weight a day.
In other words, optimum daily protein intake in urban environments is
probably in the the range between 1-1.5g per kg (0.45-0.68g/lb) of body weight.
the high-protein foods good nutritionally?
Years and decades of promoting "quality" proteins and high-protein foods have
created a myth of their nutritional superiority. The facts, however, seem to be
pointing to the opposite.
Our protein and essential
amino acids needs can be satisfied with most any natural food alone -
brown rice, wheat flour, corn,
potatoes, asparagus, broccoli, pumpkin, beef,
egg, milk, etc. - providing it is ingested in the quantity needed to fulfill
daily caloric requirement. Thus, any actual diet combining various foods
will also satisfy body's protein
and essential amino acid requirements.
There is no danger of protein deficiency for vegetarians,
or even vegans, unless they starve themselves. The concept of protein "value", or "quality" - with animal
proteins rating generally higher
than plant proteins - beside being flawed, is of secondary importance at best.
Nevertheless, it is not only given the center spot but is, evidently, also
The fact is that there is no difference in the chemical
structure and properties of any amino acid - lysine is lysine, whether it
comes from plant or animal foods. Thus,
plant or animal, the intrinsic value of an
amino acid to the body
just the same.
Labeling proteins as being of different "value", or
"quality" when coming from different foods is directly misleading. The
difference is purely quantitative
- including several percentage points lower
average absorption of plant proteins - and should be clearly presented as
such. In fact,
diets based on moderate-protein
foods are inherently
better balanced nutrients-wise, hence also healthier.
Bioavailability of heat
An important consideration not taken into account with the PDCAAS is
the form of protein
intake. Heated (cooked) proteins are denatured by higher temperatures, quickly and
completely as the temperature reaches as little as 60°C.
Denaturing is another
word for re-structuring of the protein's natural molecular form. It is also done by
the stomach acid in the process of digestion. However, if we assume that the way the stomach acid does it
enables the enzymes to optimally break down protein molecules into amino
acids, denaturing of proteins by cooking - unless identical to that caused
by the stomach acid (highly unlikely) - will result in less than optimal enzymatic
action (which works on a lock-and-key principle), and
lower amino acid
If so, at the two extreme ends, row-food diet needs to supply less
protein than all-cooked diet. In effect, cooked foods would have lower
effective protein content than what their nominal raw "label" implies.
Processed foods are also often exposed to heat, acids and/or alkali,
which means that their usable protein content is probably lower
than what their labels indicate.
There is neither consensus nor reliable studies on the subject of how much cooking
and processing lower protein bio-availability (it probably varies both,
individually and with
the protein type). It is surprising, considering how important it could
be in determining our actual protein needs. The two least likely
scenarios are: (1) no appreciable reduction in absorption/assimilation on one, and
bio-degradation on the other end. The truth is, most likely, somewhere
in between, and yet to be determined.
Raw vs. cooked differentiation is important not only protein-wise,
but for our nutritional needs in general. By preserving enzymes,
vitamins and other nutrients, as well as by
avoiding possibly harmful alteration of food molecules caused by cooking,
raw food diets are all but certain to allow for
lower caloric and
than cooked food diets. Unfortunately, there
is very little research done on this subject. Let's just recall that
lower caloric intake alone has been proven in laboratories over and
over again to be the only known factor to significantly prolong the life span.
All the facts in this lengthy consideration seem to be convincingly
turning the table against the common notion of the superiority of animal-origin
foods as a source of "quality protein". Plant foods are as
efficient protein source, and they are certainly the healthier one from
the standpoint of body's overall nutritional needs.
Highly concentrated protein foods with disproportionately
high essential amino acid content - animal proteins in general - but
also some foods of plant origin, like beans or tofu, are
bad choice for the principal protein source.
excessively high in proteins, to the detriment of other nutrients
and calories. In other words, they satisfy the need for protein much sooner than needs for other nutrients.
And vice versa, they can satisfy the need for other nutrients only
at a price of grossly excessive, unhealthy protein consumption.
Therefore, they should be consumed sparsely.
Our overall protein needs are roughly two to three
times lower, in their proportion to other basic nutrients, than what is
found in high-protein foods. Thus balanced, healthy diets are more
easily achievable when based on foods containing comparatively less protein and
more (good) fats, carbohydrates, dietary fiber and nutrients
- description that, in general, better fits foods of plant origin.
┆ NUTRITION ┆