Showdowner52
Beast
Exposing the Myths About Protein
-from the Hypertrophy-Specific Nurition Series by Bryan Haycock,
M.Sc.
http://www.beyondmuscle.com/exmytabprot.html
Myth #1: High protein intakes will not affect muscle protein
synthesis.
Fact: Greater availability of amino acids means more protein
synthesis within muscle cells.
I will concede that experiments have been performed that indicate
that a lab animal can survive on a very limited protein intake
assuming that fat and carbohydrate intake is adequate. Simply put,
the body begins to reduce that amount of amino acid oxidation in
order to spare nitrogen containing compounds. Yet can we really
apply this kind of example to adult humans trying to build muscle? I
think not.
When the body begins getting stingy with amino acids because of low
protein intake, non essential functions, such as skeletal muscle
protein synthesis, drop to minimal levels. Other functions within
the body such as the immune system, which uses glutamine primarily
of muscle origin for fuel, also begins to suffer.9 This cripples the
body's ability to cope with the stress and tissue damage induced by
intense training. Researchers even believe that currently
recommended protein intakes may actually predispose people to
illness because of the limited reserve of amino acids. Here's what
they have to say about current recommendations for protein intake:
"...It seems reasonable to conclude that the lowered rate of whole-
body and perhaps muscle protein turnover that appears to occur in
healthy adult subjects when intakes of indispensable amino acids
approximate the current international figures, would probably
diminish the individuals capacity to withstand successfully a major
stressful stimulus. Again, for those reasons, we view the
significant reduction in the rate of body protein turnover in
healthy adults, which permits them to more closely approach or even
achieve amino acid balance at currently accepted amino acid
requirement intakes, as an accommodation. Thus we further conclude
that these international requirement intakes are probably not
sufficient to maintain a desirable or adapted state."(Young VR.,
Marchini JS. Mechanisms and nutritional significance of metabolic
responses to altered intakes of protein and amino acids, with
reference to nutritional adaptation in humans. Am J Clin Nutr
1990;51:270-89) Emphasis added.
Research clearly shows that by increasing blood levels of amino
acids you increase protein synthesis in skeletal muscle. It has also
been shown that you can maintain a positive nitrogen balance for
extended periods of time and that nitrogen accretion will tend to
continue as long as protein intake is high.10 Clearly if you want to
maximize your gains in the gym you've gotta get more protein than
the average Joe.
Myth #2: You can only assimilate 30 grams of protein at one sitting.
Fact: The body has the ability to digest and assimilate much more
than 30 grams of protein from a single meal.
Speaking of high intakes of protein, people have been perpetuating
the myth that you can only assimilate ~30 grams of protein at a
time, making protein meals any greater than a 6 oz. chicken breast a
waste. This is anything but true. For example, the digestibility of
meat (i.e. beef, poultry, pork and fish) is about 97% efficient. If
you eat 25 grams of beef, you will absorb into the blood stream 97%
of the protein in that piece of meat. If, on the other hand, you eat
a 10 oz steak containing about 60 grams of protein, you will again
digest and absorb 97% of the protein. If you could only assimilate
30 grams of protein at a time, why would researchers be using in
excess of 40 grams of protein to stimulate muscle growth?1
Critics of high protein intakes may try to point out that increased
protein intake only leads to increased protein oxidation. This is
true, nevertheless, some researchers speculate that this increase in
protein oxidation following high protein intakes may initiate
something they call the "anabolic drive".13 The anabolic drive is
characterized by hyperaminoacidemia, an increase in both protein
synthesis and breakdown with an overall positive nitrogen balance.
In animals, there is a correspondent increase in anabolic hormones
such as IGF-1 and GH. Though this response is difficult to identify
in humans, an increase in lean tissue accretion does occur with
exaggerated protein intakes.14,15
The take home message is that, if you are going to maximize muscle
growth you have to minimize muscle loss, and maximize protein
synthesis. Research clearly shows this is accomplished with heavy
training, adequate calories, and very importantly high protein
consumption. This means that meals containing more than 30 grams of
protein will be the norm. Not to worry, all that protein will
certainly be used effectively by the body.
Myth #3: Protein must be rapidly digested to build muscle.
Fact: Both rapidly and slowly digested proteins offer significant
benefits to athletes.
Recent research has brought up the notion of "fast" and "slow"
proteins.11 They are designated as such according to the rate at
which they raise blood levels of amino acids after they are
consumed. Whey protein for example is considered a fast protein and
causes a rapid increase in amino acid levels. Casein on the other
hand is considered a slow protein.
Both rapid and slow proteins offer benefits to someone trying to
build muscle. Research has shown that proteins that enter the blood
stream rapidly significantly increase protein synthesis. Proteins
that enter the blood stream slowly have a pronounced effect on
protein breakdown, significantly inhibiting it even at low
quantities.
By using a combination of proteins that exhibit both fast and slow
properties one should be able not only to jump-start protein uptake
into muscle cells during a grueling workout, but also ensure that
protein synthesis is jump started and that protein break down is
kept at a minimum during the hours following their workout. Take the
fast protein before training, and a slow protein after for maximum
anabolic effect.
In summary, it is a mistake to say that a "fast" protein is better
than a "slow" protein. Both types of protein should be used in
strategic fashion to alter protein metabolism in favor of net
protein deposition (i.e. muscle growth).
Myth #4: A protein must have added peptides of specific molecular
weights to effectively build muscle.
Fact: The body¹s digestive tract makes its own variable molecular
weight peptides from the whole proteins you eat.
As soon as protein hits the stomach it is attacked by powerful
stomach acids. This acid, along with an enzyme called pepsin, serves
to change or denature the proteins structure preparing it for
further digestion in the small intestine. In the small intestine
several other enzymes work to break down the protein into various
molecular weight peptides and free amino acids. Each enzyme acts on
a specific part of the amino acid chain cleaving it in the
appropriate place. Whether you¹ve just eaten a steak, scrambled eggs
or a glass of whey protein, the end result of digestion is the same,
a full spectrum of molecular weight peptides and a moderate amount
of free amino acids perfectly suited for absorption into the body.
The small intestine has special transporters which actively pull
peptides across the brush border membrane and into intestinal cells.
All the various peptide transporters have yet to be clearly
identified. As a result of these transporters, peptides can be
actively absorbed faster than free amino acids. Within intestinal
cells, peptides are further broken down into individual amino acids
by enzymes called protease (prote = protein, ase = to split or
cleave). It has been shown that a very small percent of digested
peptides can enter the blood stream by squeezing between intestinal
cells. Even though some peptides make it into the blood stream
intact, they are quickly broken down by proteases on the surface of
liver and muscle cells. If by some small chance peptides actually
make it all the way into these cells, they are rapidly broken down
by proteases within the cell.
So you see, all this talk about adding various molecular weight
peptides simply means that they predigested an already easily
digestible protein. This simply adds to the expense of manufacturing
the protein. The added cost, of course, is passed on to the consumer.
Myth #5: Arguments over whose protein scores highest on various
methods of protein assessment will make or break your success in the
gym.
Fact: As protein intake increases the influence of protein quality
decreases. In other words, high quantity can significantly make up
for low quality.
The quantity of protein in the diet may in fact add importance to
the scoring assessment of a given protein. In fact, if you only eat
35- 45 grams a protein a day you better make sure you chose the
highest quality protein you can find. On the other hand, if you eat
quantities of protein common among bodybuilders, say 1.6 - 1.8 grams
per kilogram, the large amount of amino acids overcome slight
differences in scoring. Once you achieve a certain levels of quality
in a protein supplement, increasing it further will not
significantly change it¹s effectiveness when consumed in quantities
sufficient to pack on muscle.
Here is a quick overview of the various methods used to determine
protein quality. Keep in mind that tests used to determine protein
quality use the lower threshold of protein requirements. This
creates a metabolic environment far different from that seen in a
well fed bodybuilder or athlete.
Chemical Scoring
The most obvious way to determine the quality of a given protein is
to break it down into it's individual amino acids. This amino acid
profile is then compared to a standard profile. Egg protein is the
standard that is used in a Chemical Scoring scale for protein
quality and has a rating of 100. Take for example a protein that has
a limited amount of a specific amino acid. This amount is then com-
pared to the amount found in egg protein. If the amount in the test
protein is 75% of that found in egg then the test protein gets a
rating of 75. From this you would assume that if you could feed a
person an amount of this protein that is exactly his requirement,
you would see nitrogen excreted in the urine in the amount of 25
percent of the nitrogen fed.
Although it is relatively easy and inexpensive to do a chemical
scoring of any protein, it does not always accu-rately predict how
well the body can utilize it. So the ad-vantages of chemical scoring
in determining the quality of protein are that it is easy and
inexpensive. It's drawback is that it cannot tell you anything about
the digestibility of the protein. Chemical scoring also involves a
procedure that may destroy certain amino acids and this may lead to
inaccurate values. It is also insensitive to substances in a given
protein that can adversely effect digestibility. To discover this
variable the test would have to utilize living animals.
Biological value (BV)
Biological value (BV) scoring does utilize in vivo testing. To
determine the actual amount of a given protein that will be used by
the body it is necessary to measure not only urinary, but also fecal
losses of nitrogen when that protein is fed to human beings. This
method is used inter-nationally.
When measuring the BV of a protein source, two nitrogen studies are
done. The first study determines how much nitrogen is lost from the
body even when no protein is fed. This amount of nitrogen loss is
assumed to be inevitable and that the body will naturally lose it
regardless of the amount of nitrogen in the diet. In the second
study an amount of the protein is fed that is slightly below what is
required. As before, the nitrogen losses are then measured, but this
time they are compared to the amount of nitrogen consumed. To
determine the actual BV of the protein the re-sults are then derived
using this formula:
NPU = (N retained / N intake) x 100
This method often involves animal test subjects and is more
frequently used. It's draw backs are that if a low NPU is obtained,
it is impossible to know if it is because of a poor amino acid
profile or low digestibility.
Protein efficiency Ratio (PER)
Protein Efficiency Ratio (PER) is the best known procedure for
evaluating protein quality and is used in the United States as the
basis for regulations regarding food labeling and for the protein
RDA. This method involves rats who are fed a measured amount of
protein and weighed periodically as they grow. The PER is expressed
as:
PER = weight gain (g) / protein intake (g)
The benefits of this method are it's expense and simplicity. It's
drawbacks are that it is time consuming; the amino acid needs of
rats are not those of humans; and the amino acid needs of growing
animals are not those of adult animals (growing animals and humans
need more lysine, for example).
The PER is used to qualify statements about daily pro-tein
requirement in the United States. You are assumed to eat protein
with a PER that is equal to or better than that of the milk protein
casein; if the protein's PER is lower, you must eat more of it to
meet the RDA. Food labels have to take protein quality into
consideration, using the PER of casein as a reference point. If a
food has a protein quality equal or better than that of casein, the
RDA is 45 grams. If the protein quality is less than casein you need
65 grams for the RDA.
You may be wondering if it makes any difference if you eat your
protein from a supplement or from food. Remember that by the time it
gets absorbed into the blood stream, all your body knows is how much
of each amino acid was present in the food you ate. If you have the
money, it is certainly convenient to just drink down a high quality
protein supplement. Beyond that, it makes no difference in what form
you get your protein from as long as its a complete protein and
sufficiently digestible.
Protein digestibility-corrected amino acid score (PDCAA) As outlined
above, protein quality can be measured by the quantity of
indispensable amino acids they contain. If a protein contains all
the amino acids essential for life, it is called a complete protein
and is given a high score. Because some proteins are not as
efficiently digested there arose a need to not only test for the
amino acid composition of proteins but also for digestibility. This
type of testing is called protein digestibility-corrected amino acid
score (PDCAA). It is now a federally accepted standard for
determining protein quality for preschool aged children.
Some foods however, contain anti-nutritional factors. These factors
sometimes occur naturally like in some beans, or are a result of
heating and/or cooking, and inhibit the ability of the body to
digest and thus absorb certain amino acids. Research has shown the
PDCAA method of scoring protein often over estimates the quality of
foods containing anti-nutritional factors.12
The take home message from all this is that arguments about who¹s
protein scored highest on this test or that test are really
meaningless to the average well fed athlete.
Conclusion
Certainly exposing these myths about protein leaves advertisers with
less fodder to bombard you with. Nevertheless, getting rid of these
misconceptions will only benefit you the consumer. Knowing the truth
about protein will not only save you money but may also open up new
opportunities for muscular gains. Knowledge is the key to effective
supplementation with protein or any other supplement. Don¹t let your
purchasing decisions be controlled by false claims and misleading
pseudo science. A wise man once said, ³...know the truth, and the
truth shall set you free.² In this case, the truth will give you the
freedom to make educated decisions about protein supplementation and
the freedom to discern between marketing hype and honest
manufacturers offering quality products.
References:
1. Tipton K., Ferrando A., Phillips S., Doyle, JR D., Wolfe R. Post
exercise net protein synthesis in human muscle from orally
administered amino acids. Am. J. Physiol. 276: E628-E634, 1999
2. Bennet, W. M., A. A. Connacher, C. M. Scrimgeour, and M. J.
Rennie. The effect of amino-acid infusion on leg protein turnover
assessed by L-[15N]phenylalanine and L-[1-13C]leucine exchange. Eur.
J. Clin. Invest. 20: 37-46, 1989
3. Castellino, P., L. Luzi, D. C. Simonson, M. Haymond, and R. A.
DeFronzo. Effect of insulin and plasma amino acid concentrations on
leucine metabolism in man. J. Clin. Invest. 80: 1784-1793, 1987
4. Fryburg, D. A., L. A. Jahn, S. A. Hill, D. M. Oliveras, and E. J.
Barrett. Insulin and insulin-like growth factor-I enhance human
skeletal muscle protein anabolism during hyperaminoacidemia by
different mechanisms. J. Clin. Invest. 96: 1722-1729, 1995
5. McNulty, P. H., L. H. Young, and E. J. Barrett. Response of rat
heart and skeletal muscle protein in vivo to insulin and amino acid
infusion. Am. J. Physiol. 264 (Endocrinol. Metab. 27): E958-E965,
1993
6. Mosoni, L., M. Houlier, P. P. Mirand, G. Bayle, and J. Grizard.
Effect of amino acids alone or with insulin on muscle and liver
protein synthesis in adult and old rats. Am. J. Physiol. 264
(Endocrinol. Metab. 27): E614-E620, 1993
7. Newman, E., M. J. Heslin, R. F. Wolf, P. T. W. Pisters, and M. F.
Brennan. The effect of systemic hyperinsulinemia with concomitant
infusion of amino acids on skeletal muscle protein turnover in the
human forearm. Metabolism 43: 70-78, 1994
8. Watt, P. W., M. E. Corbett, and M. J. Rennie. Stimulation of
protein synthesis in pig skeletal muscle by infusion of amino acids
during constant insulin availability. Am. J. Physiol. 263
(Endocrinol. Metab. 26): E453-E460, 1992
9. Newsholme, A.E., Parry-Billings M. Properties of glutamine
release from muscle and its importance for the immune system. JPEN.
14 (4) supplement S63-67
10. Oddoye EA., Margen S. Nitrogen balance studies in humans: long-
term effect of high nitrogen intake on nitrogen accretion. J Nutr
109 (3): 363-77
11. Boirie Y, Dangin M, Gachon P, Vasson M-P, Maubois J-L, and
Beaufrère B. Slow and fast dietary proteins differently modulate
postprandial protein accretion (amino acid turnover / postprandial
protein anabolism / milk protein / stable isotopes) Proc. Natl.
Acad. Sci. USA Vol. 94, pp. 14930-14935, December 1997
12. Sarwar G. The Protein Digestibility-Corrected Amino Acid Score
method overestimates quality of proteins containing antinutritional
factors and of poorly digestible proteins supplemented with limiting
amino acids in rats. J. Nutr. 127: 758-764, 1997
13. Millward, D.J. Metabolic demands for amino acids and the human
dietary requirement: Millward and Rivers (1988) revisited. J. Nutr.
128: 2563S-2576S, 1998
14. Fern EB, Bielinski RN, Schutz Y. Effects of exaggerated amino
acid and protein supply in man. Experientia 1991 Feb 15;47(2):168-72
15. Dragan, GI., Vasiliu A., Georgescu E. Effect of increased supply
of protein on elite weight-lifters. In:Milk Protein T.E. Galesloot
and B.J. Tinbergen (Eds.). Wageningen The Netherlands: Pudoc, 1985,
pp. 99-103
-from the Hypertrophy-Specific Nurition Series by Bryan Haycock,
M.Sc.
http://www.beyondmuscle.com/exmytabprot.html
Myth #1: High protein intakes will not affect muscle protein
synthesis.
Fact: Greater availability of amino acids means more protein
synthesis within muscle cells.
I will concede that experiments have been performed that indicate
that a lab animal can survive on a very limited protein intake
assuming that fat and carbohydrate intake is adequate. Simply put,
the body begins to reduce that amount of amino acid oxidation in
order to spare nitrogen containing compounds. Yet can we really
apply this kind of example to adult humans trying to build muscle? I
think not.
When the body begins getting stingy with amino acids because of low
protein intake, non essential functions, such as skeletal muscle
protein synthesis, drop to minimal levels. Other functions within
the body such as the immune system, which uses glutamine primarily
of muscle origin for fuel, also begins to suffer.9 This cripples the
body's ability to cope with the stress and tissue damage induced by
intense training. Researchers even believe that currently
recommended protein intakes may actually predispose people to
illness because of the limited reserve of amino acids. Here's what
they have to say about current recommendations for protein intake:
"...It seems reasonable to conclude that the lowered rate of whole-
body and perhaps muscle protein turnover that appears to occur in
healthy adult subjects when intakes of indispensable amino acids
approximate the current international figures, would probably
diminish the individuals capacity to withstand successfully a major
stressful stimulus. Again, for those reasons, we view the
significant reduction in the rate of body protein turnover in
healthy adults, which permits them to more closely approach or even
achieve amino acid balance at currently accepted amino acid
requirement intakes, as an accommodation. Thus we further conclude
that these international requirement intakes are probably not
sufficient to maintain a desirable or adapted state."(Young VR.,
Marchini JS. Mechanisms and nutritional significance of metabolic
responses to altered intakes of protein and amino acids, with
reference to nutritional adaptation in humans. Am J Clin Nutr
1990;51:270-89) Emphasis added.
Research clearly shows that by increasing blood levels of amino
acids you increase protein synthesis in skeletal muscle. It has also
been shown that you can maintain a positive nitrogen balance for
extended periods of time and that nitrogen accretion will tend to
continue as long as protein intake is high.10 Clearly if you want to
maximize your gains in the gym you've gotta get more protein than
the average Joe.
Myth #2: You can only assimilate 30 grams of protein at one sitting.
Fact: The body has the ability to digest and assimilate much more
than 30 grams of protein from a single meal.
Speaking of high intakes of protein, people have been perpetuating
the myth that you can only assimilate ~30 grams of protein at a
time, making protein meals any greater than a 6 oz. chicken breast a
waste. This is anything but true. For example, the digestibility of
meat (i.e. beef, poultry, pork and fish) is about 97% efficient. If
you eat 25 grams of beef, you will absorb into the blood stream 97%
of the protein in that piece of meat. If, on the other hand, you eat
a 10 oz steak containing about 60 grams of protein, you will again
digest and absorb 97% of the protein. If you could only assimilate
30 grams of protein at a time, why would researchers be using in
excess of 40 grams of protein to stimulate muscle growth?1
Critics of high protein intakes may try to point out that increased
protein intake only leads to increased protein oxidation. This is
true, nevertheless, some researchers speculate that this increase in
protein oxidation following high protein intakes may initiate
something they call the "anabolic drive".13 The anabolic drive is
characterized by hyperaminoacidemia, an increase in both protein
synthesis and breakdown with an overall positive nitrogen balance.
In animals, there is a correspondent increase in anabolic hormones
such as IGF-1 and GH. Though this response is difficult to identify
in humans, an increase in lean tissue accretion does occur with
exaggerated protein intakes.14,15
The take home message is that, if you are going to maximize muscle
growth you have to minimize muscle loss, and maximize protein
synthesis. Research clearly shows this is accomplished with heavy
training, adequate calories, and very importantly high protein
consumption. This means that meals containing more than 30 grams of
protein will be the norm. Not to worry, all that protein will
certainly be used effectively by the body.
Myth #3: Protein must be rapidly digested to build muscle.
Fact: Both rapidly and slowly digested proteins offer significant
benefits to athletes.
Recent research has brought up the notion of "fast" and "slow"
proteins.11 They are designated as such according to the rate at
which they raise blood levels of amino acids after they are
consumed. Whey protein for example is considered a fast protein and
causes a rapid increase in amino acid levels. Casein on the other
hand is considered a slow protein.
Both rapid and slow proteins offer benefits to someone trying to
build muscle. Research has shown that proteins that enter the blood
stream rapidly significantly increase protein synthesis. Proteins
that enter the blood stream slowly have a pronounced effect on
protein breakdown, significantly inhibiting it even at low
quantities.
By using a combination of proteins that exhibit both fast and slow
properties one should be able not only to jump-start protein uptake
into muscle cells during a grueling workout, but also ensure that
protein synthesis is jump started and that protein break down is
kept at a minimum during the hours following their workout. Take the
fast protein before training, and a slow protein after for maximum
anabolic effect.
In summary, it is a mistake to say that a "fast" protein is better
than a "slow" protein. Both types of protein should be used in
strategic fashion to alter protein metabolism in favor of net
protein deposition (i.e. muscle growth).
Myth #4: A protein must have added peptides of specific molecular
weights to effectively build muscle.
Fact: The body¹s digestive tract makes its own variable molecular
weight peptides from the whole proteins you eat.
As soon as protein hits the stomach it is attacked by powerful
stomach acids. This acid, along with an enzyme called pepsin, serves
to change or denature the proteins structure preparing it for
further digestion in the small intestine. In the small intestine
several other enzymes work to break down the protein into various
molecular weight peptides and free amino acids. Each enzyme acts on
a specific part of the amino acid chain cleaving it in the
appropriate place. Whether you¹ve just eaten a steak, scrambled eggs
or a glass of whey protein, the end result of digestion is the same,
a full spectrum of molecular weight peptides and a moderate amount
of free amino acids perfectly suited for absorption into the body.
The small intestine has special transporters which actively pull
peptides across the brush border membrane and into intestinal cells.
All the various peptide transporters have yet to be clearly
identified. As a result of these transporters, peptides can be
actively absorbed faster than free amino acids. Within intestinal
cells, peptides are further broken down into individual amino acids
by enzymes called protease (prote = protein, ase = to split or
cleave). It has been shown that a very small percent of digested
peptides can enter the blood stream by squeezing between intestinal
cells. Even though some peptides make it into the blood stream
intact, they are quickly broken down by proteases on the surface of
liver and muscle cells. If by some small chance peptides actually
make it all the way into these cells, they are rapidly broken down
by proteases within the cell.
So you see, all this talk about adding various molecular weight
peptides simply means that they predigested an already easily
digestible protein. This simply adds to the expense of manufacturing
the protein. The added cost, of course, is passed on to the consumer.
Myth #5: Arguments over whose protein scores highest on various
methods of protein assessment will make or break your success in the
gym.
Fact: As protein intake increases the influence of protein quality
decreases. In other words, high quantity can significantly make up
for low quality.
The quantity of protein in the diet may in fact add importance to
the scoring assessment of a given protein. In fact, if you only eat
35- 45 grams a protein a day you better make sure you chose the
highest quality protein you can find. On the other hand, if you eat
quantities of protein common among bodybuilders, say 1.6 - 1.8 grams
per kilogram, the large amount of amino acids overcome slight
differences in scoring. Once you achieve a certain levels of quality
in a protein supplement, increasing it further will not
significantly change it¹s effectiveness when consumed in quantities
sufficient to pack on muscle.
Here is a quick overview of the various methods used to determine
protein quality. Keep in mind that tests used to determine protein
quality use the lower threshold of protein requirements. This
creates a metabolic environment far different from that seen in a
well fed bodybuilder or athlete.
Chemical Scoring
The most obvious way to determine the quality of a given protein is
to break it down into it's individual amino acids. This amino acid
profile is then compared to a standard profile. Egg protein is the
standard that is used in a Chemical Scoring scale for protein
quality and has a rating of 100. Take for example a protein that has
a limited amount of a specific amino acid. This amount is then com-
pared to the amount found in egg protein. If the amount in the test
protein is 75% of that found in egg then the test protein gets a
rating of 75. From this you would assume that if you could feed a
person an amount of this protein that is exactly his requirement,
you would see nitrogen excreted in the urine in the amount of 25
percent of the nitrogen fed.
Although it is relatively easy and inexpensive to do a chemical
scoring of any protein, it does not always accu-rately predict how
well the body can utilize it. So the ad-vantages of chemical scoring
in determining the quality of protein are that it is easy and
inexpensive. It's drawback is that it cannot tell you anything about
the digestibility of the protein. Chemical scoring also involves a
procedure that may destroy certain amino acids and this may lead to
inaccurate values. It is also insensitive to substances in a given
protein that can adversely effect digestibility. To discover this
variable the test would have to utilize living animals.
Biological value (BV)
Biological value (BV) scoring does utilize in vivo testing. To
determine the actual amount of a given protein that will be used by
the body it is necessary to measure not only urinary, but also fecal
losses of nitrogen when that protein is fed to human beings. This
method is used inter-nationally.
When measuring the BV of a protein source, two nitrogen studies are
done. The first study determines how much nitrogen is lost from the
body even when no protein is fed. This amount of nitrogen loss is
assumed to be inevitable and that the body will naturally lose it
regardless of the amount of nitrogen in the diet. In the second
study an amount of the protein is fed that is slightly below what is
required. As before, the nitrogen losses are then measured, but this
time they are compared to the amount of nitrogen consumed. To
determine the actual BV of the protein the re-sults are then derived
using this formula:
NPU = (N retained / N intake) x 100
This method often involves animal test subjects and is more
frequently used. It's draw backs are that if a low NPU is obtained,
it is impossible to know if it is because of a poor amino acid
profile or low digestibility.
Protein efficiency Ratio (PER)
Protein Efficiency Ratio (PER) is the best known procedure for
evaluating protein quality and is used in the United States as the
basis for regulations regarding food labeling and for the protein
RDA. This method involves rats who are fed a measured amount of
protein and weighed periodically as they grow. The PER is expressed
as:
PER = weight gain (g) / protein intake (g)
The benefits of this method are it's expense and simplicity. It's
drawbacks are that it is time consuming; the amino acid needs of
rats are not those of humans; and the amino acid needs of growing
animals are not those of adult animals (growing animals and humans
need more lysine, for example).
The PER is used to qualify statements about daily pro-tein
requirement in the United States. You are assumed to eat protein
with a PER that is equal to or better than that of the milk protein
casein; if the protein's PER is lower, you must eat more of it to
meet the RDA. Food labels have to take protein quality into
consideration, using the PER of casein as a reference point. If a
food has a protein quality equal or better than that of casein, the
RDA is 45 grams. If the protein quality is less than casein you need
65 grams for the RDA.
You may be wondering if it makes any difference if you eat your
protein from a supplement or from food. Remember that by the time it
gets absorbed into the blood stream, all your body knows is how much
of each amino acid was present in the food you ate. If you have the
money, it is certainly convenient to just drink down a high quality
protein supplement. Beyond that, it makes no difference in what form
you get your protein from as long as its a complete protein and
sufficiently digestible.
Protein digestibility-corrected amino acid score (PDCAA) As outlined
above, protein quality can be measured by the quantity of
indispensable amino acids they contain. If a protein contains all
the amino acids essential for life, it is called a complete protein
and is given a high score. Because some proteins are not as
efficiently digested there arose a need to not only test for the
amino acid composition of proteins but also for digestibility. This
type of testing is called protein digestibility-corrected amino acid
score (PDCAA). It is now a federally accepted standard for
determining protein quality for preschool aged children.
Some foods however, contain anti-nutritional factors. These factors
sometimes occur naturally like in some beans, or are a result of
heating and/or cooking, and inhibit the ability of the body to
digest and thus absorb certain amino acids. Research has shown the
PDCAA method of scoring protein often over estimates the quality of
foods containing anti-nutritional factors.12
The take home message from all this is that arguments about who¹s
protein scored highest on this test or that test are really
meaningless to the average well fed athlete.
Conclusion
Certainly exposing these myths about protein leaves advertisers with
less fodder to bombard you with. Nevertheless, getting rid of these
misconceptions will only benefit you the consumer. Knowing the truth
about protein will not only save you money but may also open up new
opportunities for muscular gains. Knowledge is the key to effective
supplementation with protein or any other supplement. Don¹t let your
purchasing decisions be controlled by false claims and misleading
pseudo science. A wise man once said, ³...know the truth, and the
truth shall set you free.² In this case, the truth will give you the
freedom to make educated decisions about protein supplementation and
the freedom to discern between marketing hype and honest
manufacturers offering quality products.
References:
1. Tipton K., Ferrando A., Phillips S., Doyle, JR D., Wolfe R. Post
exercise net protein synthesis in human muscle from orally
administered amino acids. Am. J. Physiol. 276: E628-E634, 1999
2. Bennet, W. M., A. A. Connacher, C. M. Scrimgeour, and M. J.
Rennie. The effect of amino-acid infusion on leg protein turnover
assessed by L-[15N]phenylalanine and L-[1-13C]leucine exchange. Eur.
J. Clin. Invest. 20: 37-46, 1989
3. Castellino, P., L. Luzi, D. C. Simonson, M. Haymond, and R. A.
DeFronzo. Effect of insulin and plasma amino acid concentrations on
leucine metabolism in man. J. Clin. Invest. 80: 1784-1793, 1987
4. Fryburg, D. A., L. A. Jahn, S. A. Hill, D. M. Oliveras, and E. J.
Barrett. Insulin and insulin-like growth factor-I enhance human
skeletal muscle protein anabolism during hyperaminoacidemia by
different mechanisms. J. Clin. Invest. 96: 1722-1729, 1995
5. McNulty, P. H., L. H. Young, and E. J. Barrett. Response of rat
heart and skeletal muscle protein in vivo to insulin and amino acid
infusion. Am. J. Physiol. 264 (Endocrinol. Metab. 27): E958-E965,
1993
6. Mosoni, L., M. Houlier, P. P. Mirand, G. Bayle, and J. Grizard.
Effect of amino acids alone or with insulin on muscle and liver
protein synthesis in adult and old rats. Am. J. Physiol. 264
(Endocrinol. Metab. 27): E614-E620, 1993
7. Newman, E., M. J. Heslin, R. F. Wolf, P. T. W. Pisters, and M. F.
Brennan. The effect of systemic hyperinsulinemia with concomitant
infusion of amino acids on skeletal muscle protein turnover in the
human forearm. Metabolism 43: 70-78, 1994
8. Watt, P. W., M. E. Corbett, and M. J. Rennie. Stimulation of
protein synthesis in pig skeletal muscle by infusion of amino acids
during constant insulin availability. Am. J. Physiol. 263
(Endocrinol. Metab. 26): E453-E460, 1992
9. Newsholme, A.E., Parry-Billings M. Properties of glutamine
release from muscle and its importance for the immune system. JPEN.
14 (4) supplement S63-67
10. Oddoye EA., Margen S. Nitrogen balance studies in humans: long-
term effect of high nitrogen intake on nitrogen accretion. J Nutr
109 (3): 363-77
11. Boirie Y, Dangin M, Gachon P, Vasson M-P, Maubois J-L, and
Beaufrère B. Slow and fast dietary proteins differently modulate
postprandial protein accretion (amino acid turnover / postprandial
protein anabolism / milk protein / stable isotopes) Proc. Natl.
Acad. Sci. USA Vol. 94, pp. 14930-14935, December 1997
12. Sarwar G. The Protein Digestibility-Corrected Amino Acid Score
method overestimates quality of proteins containing antinutritional
factors and of poorly digestible proteins supplemented with limiting
amino acids in rats. J. Nutr. 127: 758-764, 1997
13. Millward, D.J. Metabolic demands for amino acids and the human
dietary requirement: Millward and Rivers (1988) revisited. J. Nutr.
128: 2563S-2576S, 1998
14. Fern EB, Bielinski RN, Schutz Y. Effects of exaggerated amino
acid and protein supply in man. Experientia 1991 Feb 15;47(2):168-72
15. Dragan, GI., Vasiliu A., Georgescu E. Effect of increased supply
of protein on elite weight-lifters. In:Milk Protein T.E. Galesloot
and B.J. Tinbergen (Eds.). Wageningen The Netherlands: Pudoc, 1985,
pp. 99-103
Last edited:
