![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Laboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, MA 02139
3To whom correspondence should be addressed.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
KEY WORDS: • infants • children • adults • factorial method • protein quality • protein requirements
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
|
Nitrogen (protein) requirements |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
With respect to the requirements for total nitrogen (protein), the
current international recommendations are now broadly accepted
(FAO/WHO/UNU 1985
) (Table 1
). Some refinements in these recommendations have been proposed more
recently by the International Dietary Energy Consultative Group (IDECG)
for the protein needs of infants and young children (Dewey et al. 1996
). Because there are some differences between these
1996 values and those proposed in the 1985 United Nations (UN) report,
it is worth summarizing the basis for and the magnitude of the
differences. Some subsequent comments about the protein needs in
elderly persons are also in order.
|
: (1) for infants <6 mo old, the recommendation is derived
from data on breast milk protein intake, and (2) for infants
>6 mo old and for children and adolescents, a modified factorial
approach was used in which i) the maintenance requirement at
6 mo was taken to be 120 mg N · kg-1 ·
d-1, declining to 103 mg N ·
kg-1 · d-1 by age 18,
ii) a growth component was estimated and to which a 50%
addition was made to provide a margin of safety because growth rates
vary from day to day and because protein is not "stored" in times
of a relative excess in intake, iii) the fractional
efficiency of nitrogen utilization from high quality protein sources
for both maintenance and growth was taken to be 0.7 and iv)
the coefficients of variation (CV) for maintenance and growth were
taken to be 12.5 and 35%, respectively, for purposes of calculating
the total CV and a recommended safe protein intake level.
|
, the basis is presented on which the protein requirements in adult men
and women, including elderly persons, are estimated. Results from both
short-term and long-term nitrogen balance studies were used to
set a mean requirement of 0.6 g high quality protein ·
kg-1 · d-1 for men.
From this, a safe protein intake level of 0.75 g protein · kg-1 · d-1 was set for
men, women and elderly persons. Additional estimates, as also indicated
in this table, were made to arrive at the recommendations for pregnant
and lactating women.
|
As mentioned, the IDECG group (Dewey et al. 1996
)
reevaluated the bases used to derive the 1985 UN recommendations for
infants, and this expert group revised the 1985 UN estimates of intakes
of breast-fed infants. The revision took into account new data for
estimates of 1) the intake of breast milk; 2) the
content of protein nitrogen and nonprotein nitrogen; 3) the
efficiency of retention of nonprotein N, which the IDECG group took to
be 46–61%, compared with an assumed value of 100% used by the UN;
and 4) body weights of breast-fed rather than of
bottle-fed babies. The 1996 IDECG protein intake estimates for
breast-fed infants are shown in Table 4
, and they are compared with the 1985 FAO/WHO/UNU values; the 1996 values
are ~10–26% lower than the 1985 values, depending on age.
|
A comparison of the safe levels of protein intake for selected
groups of older infants and children as proposed in 1985 by the UN and
in 1996 by the IDECG is given in Table 5
. The revised estimates are ~25–30% lower than those made in the
1985 FAO/WHO/UNU report. It remains to be seen whether the new IDECG
recommendations will be used in a future UN revision of current
international (FAO/WHO/UNU) (Table 1)
.
|
The 1985 FAO/WHO/UNU protein requirements and recommendations for
dietary protein intakes in adults have not yet been revisited by an
international expert group. However, in view of the rapidly growing
number of elderly subjects in the developed, as well as developing,
regions of the world (World Health Organization 1998
),
it is important that increased attention also be given to the nitrogen
and amino acid needs of this sector of the population. The UN group
(FAO/WHO/UNU 1985
) concluded that the safe intake of
protein should not be lower than 0.7 g ·
kg-1 · d-1 for older
adults and elderly persons. However, there has been limited additional
study on the protein requirements of elderly persons since that
recommendation was made. Thus, Campbell and others (Campbell et al. 1994
, Campbell and Evans 1996
) have more
recently proposed a higher safe protein intake of 1–1.25 g ·
kg-1 · d-1 based on
their own investigations and a reassessment of the literature. In
addition, in their review of the published literature, Millward and Roberts (1996
) concluded that it has not been demonstrated
unequivocally there is an increase with progressive adult age in the
mean protein requirement. Indeed, the group at the University of Surrey
concluded from 13C-leucine tracer studies that
the apparent protein requirement is lower in elderly persons on the
basis of body weight as well as fat free mass (Fereday et al. 1997b
, Millward et al. 1997
). However, the
experimental approach used by these investigators has its inherent
limitations, and in particular, their study subjects had not been
adjusted to a standard diet before their of the tracer studies. Thus,
the nutritional requirement implications of the metabolic studies by
Millward, Fereday and their colleagues remain somewhat uncertain. Some
years ago, Young et al. (1982
) proposed that because of
the increased morbidity rate and disease burden in elderly persons, a
rational and sound recommendation would be in the region of 1 g
good quality protein · kg-1 ·
d-1 for this age group. There seems little
reason not to follow this recommendation, based on the foregoing.
Clearly, further research into the protein requirements in this age
group would be highly desirable, although it is may be clear from this
overview that the nitrogen requirements at various stages in the life
of generally healthy individuals are not currently a topic that arouses
strong debate or major controversy. This differentiates it from that of
the requirements for IAA, which we consider later. However, before
doing so, it is worth noting briefly, with reference to nitrogen
requirements, that there is much current research interest on the
metabolism of and possibly conditional needs for a number of the
so-called dispensable amino acids. These include studies on
glutamine, arginine, cyst(e)ine, tyrosine, glycine and proline, which
we do not review here. In addition, new research on the in vivo
metabolism of glutamic acid (see Reeds 2000
), which
plays a pivotal role in the transactions and economy of body nitrogen
(Young and Ajami, 2000
), coupled with the possibility
that nonamino nitrogen sources may not be effectively used for the net
synthesis of 
-amino N (see, e.g., Young et al. 2000
),
has raised again the question of the importance of the qualitative
nature of the so-called nonspecific nitrogen component of the total
nitrogen requirement. It appears to us that a distinct possibility
exists that a preformed source of -amino nitrogen, possibly
preferably as glutamic acid, is a necessary component of an optimal
dietary protein (nitrogen) intake, in addition to that of the IAA. If
this is so, this adds a new perspective to our metabolic understanding
and the nutritional significance of the total protein requirement in
humans.
|
Requirements for indispensable amino acids |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
We (Young 1991
and 1999
, Young and Marchini 1990
, Young et al. 1987) have reviewed, on a
number of occasions, the state-of-the-art with respect to the
definition and determination of the quantitative needs for the specific
IAA. Our starting point in the present overview is the 1985 FAO/WHO/UNU
recommendations for four age groups; these are shown in Table 6
. These values indicate that the requirements, per unit body weight,
decline substantially between infancy and adulthood, with the
requirement for the total of the IAA falling from ~714 mg ·
kg-1 · d-1 in 3- to
4-mo-old infants to ~84 mg · kg-1 ·
d-1 in the adult. When expressed per unit of
safe protein intake (less histidine), the pattern of change with growth
development is also marked in that there is a fall in the total
IAA-to-protein ratio, with the value for infants being 434 mg ·
g-1 · protein-1
compared with adults, in whom the comparative value is 111 mg ·
g-1 · protein-1.
The biological basis for this dramatic change in the proportion of IAA
to total nitrogen is unclear to us, particularly because daily protein
maintenance accounts for such a high proportion of the total amino acid
requirement, even in the young. Earlier, we (Young 1991
)
had estimated that for the 2-y-old child, maintenance accounts for
80–90% of the total protein requirement, and Millward (1999
), using a somewhat different data set, suggested a value
of ~85%. Therefore, it seemed likely to us, some years ago, that the
picture of a greater change in the IAA requirements relative to the
total protein requirements that emerges from the UN data may be a
reflection of experimental approaches and their limitations for the
determination of requirements rather than a reflection of true changes
in the biology of human protein and amino acid metabolism with the
development and achievement of maturity.
|
, Young and Marchini 1990
,
Young et al. 1989
) discussed the various experimental
limitations of the amino acid requirement values shown in Table 6
, and
they will not be repeated here, except to make the following points:
1) the requirements for infants are derived from a
combination of the lowest intakes that were found to be adequate for
all infants tested in the studies by Holt and Snyderman (1965
) or those calculated by Fomon and Filer (1967
) that were the lowest intakes of amino acids by infants
fed a variety of formulas at levels that maintained adequate growth;
2) the values for the preschool-age child were obtained
from studies carried out at the Institute of Nutrition for Central
America and Panama, Guatemala, of which the data were presented in only
summary form at a conference proceedings (Pineda et al. 1981
, Torun et al. 1981
); 3) the
values for school-age children are limited to a series of careful
studies carried by Nakagawa et al. (1964
) in Japan; and
4) the adult values are based on the studies by Rose (1957
) in men and from similar investigations by others in
women (summarized by Irwin and Hegsted 1971
); the adult
values given in this 1985 report (Table 6)
are no longer considered to
be acceptable or nutritionally relevant (Working Group 1996
).
The amino acid requirements in infants also were reassessed by IDECG
(Dewey et al. 1996
) using a factorial approach. The
IDECG values for 3- to 6-mo-old infants are summarized in Table 7
and compared with the 1985 FAO/WHO/UNU
estimates (which were taken from the 1973 FAO/WHO report), as well as with those suggested recently by
Millward (1999
), which were also derived via a factorial
method. There are some differences, although not substantial, between
the IDECG and Millward (1999
) factorial estimates, due
essentially to differences in the amino acid requirements assumed for
maintenance. However, both of these factorially derived estimates of
the amino acid requirements (expressed per kg body weight) in 3- to
6-mo-old infants are substantially lower than those proposed in 1985
FAOWHO/UNU report. This is also true for the infant amino acid
requirement values, when expressed per unit of protein, due here to the
fact that the UN values are based on the amino acid composition of
breast milk protein rather on experimentally derived requirement
values.
|
, giving the FAO/WHO/UNU direct estimates and the factorially
derived values of Millward (1999
). IDECG did not
reassess the amino acid requirement values for preschool- or
school-age children. The differences for the preschool child
between the two values summarized here and expressed per kg per day are
relatively large for all of the amino acids.
Finally, the factorially derived estimates of the amino acid
requirement in adults made by Millward (1999
) are also
compared in Table 7
with the 1985 FAO/WHO/UNU values. For this age
group, the values of Millward (1999
) are consistently
higher than the FAO (UN) values. The even more recent estimates of the
lysine requirement made by Millward (2000
), based on
13C-leucine kinetic studies (shown in Table 7
in
parentheses) are, per unit of protein, approximately two to almost
three times that proposed by the UN group. Furthermore, for reasons
given later, the recent lysine requirement values proposed by
Millward (2000
) are the important ones to be considered,
whereas at the same time, they have probably been underestimated.
|
Massachusetts Institute of Technology requirement values and pattern |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
, which were reported in 1985
(FAO/WHO/UNU 1985
), have been widely used
internationally, and they were based on nitrogen balance studies by
Rose and others in the 1950s and 1960s (Irwin and Hegsted 1971
, Rose 1957
, Williams et al. 1974
). Furthermore, the requirement values proposed by
Millward (1999
) and summarized in Table 7
are also
derived from the same nitrogen balance studies, except for his
13C-tracer based estimates of the requirements
for lysine (Millward 2000
). However, the validity of
these earlier nitrogen balance studies and the interpretations drawn
from them have been seriously criticized (Young 1991
and 1999
, Young and Marchini 1990
, Young et al. 1989
). Therefore, in our laboratories at the Massachusetts
Institute of Technology (MIT) Clinical Research Center, we have been
developing and refining a new method of estimating IAA requirements
based. In its latest version, the method involves an infusion for
24 h of an amino acid labeled with 13C and
measurement of 13CO2
output. From this information, the carbon balance can be calculated,
and if the IAA of interest is given at different levels of intake, a
value for the requirement can be obtained by estimating the minimal
intake necessary to maintain balance.
Briefly, our overall approach has involved both the application of
13C-labeled amino acid carbon balance at varying
test levels of amino acid intake (Young 1999
,
Young et al. 1987) and the prediction of the obligatory
amino acid losses and intakes necessary to just balance these,
especially for the amino acids that we have not yet studied directly
using 13C tracers (Young and El-Khoury 1995
).
Our working definition of the requirement for an IAA in a healthy individual is "that minimal intake level which represents a single point on a dose-response curve and that is sufficient to maintain a specific criterion of nutritional adequacy (such as growth performance, body composition, body amino acid balance, or measure of organ [liver, muscle] or system [immuno/defense, nervous] function)." For practical reasons we have chosen to use body amino acid balance, as determined by the difference between the intake of the test amino acid (e.g., leucine or lysine) and the whole body oxidation of that amino acid, as measured by the appearance of the 13C label of the amino acid in expired carbon dioxide. Noninvasive measures of specific organ or system function have not yet been sufficiently explored or developed for use in estimating the requirements for specific IAA.
From our initial series of 13C-tracer studies, we
estimated the requirements in adults for leucine, lysine, threonine and
methionine (without dietary cysteine) to be 30–40, 30, 15 and 13 mg
· kg-1 · d-1,
respectively (Young et al. 1989
). Except for the sulfur
amino acid requirement, these values are far higher than the 1985
FAO/WHO/UNU values for adults shown in Table 7
. In addition, we
attempted to predict the requirements for those IAA that we had not yet
studied with the aid of tracer techniques. This prediction was based on
assumed obligatory oxidative amino acid losses (Young and El-Khoury 1995
), and we have recently validated these
estimates (Raguso et al. 1999
).
Our earlier 13C-tracer studies provided an
initial basis for setting tentative, new requirement values for adults.
These studies involve relatively short-term tracer infusion
protocols lasting for 3–8 hours. It was then considered important to
assess the 24-h kinetics and balance of the test amino acids, so we
have undertaken a major series of 24-h tracer studies, beginning with
leucine as the test amino acid (El-Khoury et al. 1994a
, 1994b
and 1995
). This permitted us to validate our technique and to
provide a stronger basis for follow-up and interpretation of 24-h
studies with other amino acids. Thus, more recently, we obtained
extensive data on the requirements for the aromatic amino acids
(Basile-Filho et al. 1997
and 1998
, Sánchez et al. 1995
and 1996
) and for lysine (El-Khoury et al. 1998
and 2000
).
In Table 8
a summary of rates of lysine oxidation and estimates of balance are
given for two test intakes of lysine: a low intake of 15.5 mg ·
kg-1 · d-1 [~30%
higher than the UN upper requirement value (FAO/WHO/UNU 1985
) of 12 mg · kg-1 ·
d-1] and an intermediate intake of 29.1 mg ·
kg-1 · d-1 [similar to
the tentative new MIT requirement of 30 mg ·
kg-1 · d-1
(El-Khoury et al. 2000)
]. Balance was significantly
negative at the low intake, but body lysine equilibrium was achieved at
the tentative MIT requirement intake level.
|
is that the daily
rate of oxidation was estimated to be almost identical for the two test
lysine intake levels. Studies in sheep (Brooks et al. 1973
) and rats (Bergner et al. 1978
,
Brooks et al. 1972
) have shown that at intakes
approximating a requirement intake of lysine and below the rate of
lysine, oxidation is essentially constant. When this physiological
requirement intake level is exceeded, the oxidation increases with
further increases in amino acid intake. Hence, our findings in healthy
adults are consistent with the view that the two test lysine intakes
studied here fall in the range approximating a minimum physiological
requirement level and below.
The preceding point is further substantiated when the present oxidation
data are evaluated against our previous data obtained at a generous
lysine intake (77 mg · kg-1 ·
d-1) (El-Khoury et al. 1998
). At
this latter intake, the rate of lysine oxidation was determined to be
minimally 70 mg · kg-1 ·
d-1, although in reality it was more likely to
approximate the intake. Thus, when the dietary intake is reduced to a
level of ~30 mg · kg-1 ·
d-1, oxidation declined almost quantitatively,
but with a further intake reduction below this level, the rate of
oxidation remains essentially constant. Hence, when these two lysine
tracer studies (El-Khoury et al. 1998
and 2000
) are
viewed together, it is apparent that the minimum physiological
requirement approximates (or is possibly higher than) the intermediate
lysine studied in our recent investigation.
Other lines of evidence support our proposal that the lysine
requirement is ~30 mg · kg-1 ·
d-1; these have been discussed and reviewed (Young and El-Khoury 1996
) and now include the results of our
(Rand and Young 1999
) recent analysis of the earlier
nitrogen balance data of Jones et al. (1956
) and the
findings in the studies by the Toronto group using the indicator amino
acid oxidation technique for determining amino acid requirements. Thus,
on the basis of the oxidation of
L-[13C]phenylalanine, as the
indicator amino acid, Zello et al. (1993
) concluded that
"the lysine requirement of adult males is three times greater than
the World Health recommendation of 12 mg/kg/d." Subsequent studies by
this group (Duncan et al. 1996
) confirmed their previous
estimate of ~40 mg · kg-1 ·
d-1, which is somewhat higher than our new
tentative estimate of 30 mg · kg-1 ·
d-1.
Furthermore, Millward and colleagues (Fereday et al. 1995
and 1997a
, Millward 2000
) applied a
13C-leucine tracer model of postprandial protein
utilization to evaluate the efficiency of protein retention when small
or large meals supplying either cow’s milk proteins or wheat protein
were the major nitrogen components of these meals. Based on the
13C-tracer data, they (Millward 2000
) estimated that the mean lysine requirement in healthy
adults is 23–27 mg · kg-1 ·
d-1, a figure that is close to our proposed
value of 30 mg · kg-1 ·
d-1. The recent data of Millward are very
similar to those we had predicted a few years ago (Young and El-Khoury 1996
). Also, in 24-h
13C-leucine indicator amino acid
oxidation/balance studies carried out in Bangalore, India, in healthy
adult Indian subjects, Kurpad et al. (1998
) provided
evidence to further support the 30 mg · kg-1
· d-1 lysine requirement figure. This has been
confirmed in a more extensive study carried out at the Indian center,
and the results obtained are now being summarized and prepared for
publication (Kurpad, A. V., Raj, T., El-Khoury, A. E., et
al., unpublished data).
Finally, the proposed MIT lysine requirement value is supported by
nitrogen balance data on the nutritional quality of whole wheat
proteins. Thus, the lysine content of wheat (Sikka et al. 1975
) is summarized in Table 9
, together with the lysine content of a number of international amino
acid scoring patterns. In addition, the usual concentration of lysine
in most animal proteins and legumes (Pellett and Young 1990
) and that for the MIT requirement pattern are also given
for comparison in Table 9
. Therefore, if an amino acid score ([amino
acid content in the food protein/amino acid content in the reference
amino acid requirement pattern] x 100) is calculated for wheat four,
it would be >100 when the FAO/WHO/UNU (1985
) amino acid
requirement pattern for the adult is used as the reference pattern
(Table 10
). This means that the nutritional value of wheat is predicted to be
equal to that of high quality animal protein foods, such as milk, egg
or meat. On the other hand, for scoring purposes, the
FAO/WHO/UNU (1985
) preschool amino acid pattern (or the FAO/WHO pattern 1991
) predicts a relative nutritional quality of 41%
(lysine is limiting); and with the MIT pattern, the score predicts a
slightly higher value of 48%. In each case, lysine is determined to be
the most limiting amino acid.
|
|
). The nitrogen balance
response to graded intakes of test dietary protein in healthy adults,
expressed as relative protein value (RPV = [N balance slope with
wheat/N balance slope with reference protein] x 100), was found to be
54 for whole wheat protein, using beef protein as a reference.
Expressed as relative nitrogen requirement (RNR = 1/[amount of
wheat protein to achieve nitrogen balance in 97.5% of population
- amount of beef protein] x 100), the response was ~56
(Table 11
). The MIT amino acid requirement pattern predicted a value of 48.
Hence, there is very good agreement between these experimentally
derived (nitrogen balance) and predicted (from amino acid score)
estimates of the nutritional quality of whole wheat proteins when the
MIT lysine requirement value is used to generate the reference amino
acid scoring pattern. In contrast, use of the 1985 FAO/WHO/UNU adult
amino acid pattern gives an invalid prediction of the nutritional value
of wheat protein. Again, therefore, these observations support the
conclusion that the 1985 FAO/WHO/UNU lysine requirement value of 12 mg
· kg-1 · d-1 for the
adult should be discarded. They also provide additional justification
for the tentative working value of 30 mg ·
kg-1 · d-1 proposed
above (or 50 mg lysine/g protein).
|
and compared with those proposed by FAO/WHO/UNU (1985
)
and by Millward (1999
and 2000
). The nutritionally
relevant amino acids, from a public health nutritional standpoint, are,
first, lysine, followed by the sulfur amino acids, threonine and
perhaps tryptophan (FAO/WHO/UNU 1985
). It may be seen
that there is evidently relatively good agreement between the MIT
values and those proposed recently by Millward (1999
and 2000)
for these amino acids in healthy adults (Table 12)
.
|
). We (Fukagawa et al. 1998
), however, studied methionine/cyst(e)ine
relationships in elderly subjects, and our initial data suggest that
elderly persons may adjust less well to a reduction in the dietary
intake of the sulfur amino acids than do young adults. There is,
clearly, a need to establish with great confidence whether the amino
acid requirement values for healthy young adults apply as well to the
healthy elderly population. |
Importance of revised requirement values |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
). It can be seen from Table 13
that the amino acid requirement pattern (expressed per unit of protein)
for the school-age child has higher lysine and threonine values
than for the MIT pattern but similar values for the other amino acids.
The higher FAO/WHO/UNU lysine value has been suggested by
Millward (1994
) to be due to the possibility that the
preschool-age children who participated in the amino acid
requirement studies at the Institute of Nutrition for Central America
and Panama had not fully recovered from earlier protein-energy
malnutrition. However, it can equally well be argued that this is not
an adequate explanation, because rapid growth during recovery might be
expected to be associated with a higher efficiency of lysine (or other
IAA) utilization and retention than would be the case in the fully
replete state. Nevertheless, we consider that a requirement value of 50
mg lysine/g protein should be adequate to support the needs for growth
in healthy preschool-age children. Thus, the 1996 IDECG group
(Dewey et al. 1996
) proposed a mean lysine requirement
of 63 mg · kg-1 · d-1
for 3- to 6-mo-old infants; when expressed in relation to the IDECG
proposed mean protein requirement of ~1.06 protein ·
kg-1 · d-1 for the 3-
to 4-mo-old age group, this would give a mean value of 59 mg
lysine · kg-1 ·
d-1 for a young infant who is gaining ~56 mg
N · kg-1 · d-1.
The comparable rate gain in the 2-y-old child might be ~13 mg n
· kg-1 · d-1, so this
would support our view that a lysine requirement of 50 mg/g protein
should be sufficient to meet the needs of the preschool-age
child. A similar argument can be made for the adequacy of the threonine
content in the MIT amino acid requirement pattern, with respect to its
application to the preschool-age group.
|
In Table 14
we present the amino acid scores (for lysine and the sulfur amino
acids) of wheat and milk and a combination of the two sources when the
estimates are based on different reference amino acid requirement
patterns. This table shows that when the 1985 FAO/WHO/UNU amino acid
requirement pattern for adults is used, the nutritional qualities of
wheat and milk are both very high and equal to each other, when each
are consumed as a sole source of dietary protein. On the other hand,
the more recent estimates of Millward (1999
and 2000)
of
the lysine requirement in adults and that in the MIT amino acid
requirement pattern lead to the conclusion that wheat has a protein
nutritional value much lower than that of milk and that when milk is
added to wheat in the proportion of 40% of milk protein nitrogen and
the remainder from wheat, a high quality protein mixture is obtained.
|
) recommendations would make the
question of dietary protein quality totally unimportant, except perhaps
for the infant and young child. On the basis of the totality of the
evidence, this latter position would be hard to justify. We reviewed the current international recommendations concerning the nitrogen and amino acid requirements of healthy individuals from infancy to the later years of adult life. Changes in the recommendations for protein that have been made, since those issued in 1985 by FAO/WHO/UNU, by the IDECG are described. The current international requirements for the specific IAA are critiqued briefly, and the rationale and basis for the MIT amino acid requirement pattern are presented. The evidence is then summarized that supports its use in practical considerations of human protein nutrition. It is proposed that this MIT pattern provides the current best estimates of the minimum physiological requirements for IAA in children and adults. It is further concluded that it would be difficult to argue for the continued use of the amino acid requirement values proposed by FAO/WHO/UNU in 1985 in the planning and assessment of dietary protein intakes for population groups worldwide.
|
FOOTNOTES |
|---|
2 Supported by National Institutes of Health
Grants RR88, DK15856, DK42101, and P-30-DK-40561 and by the
Nestlé Research Foundation, Lausanne, Switzerland, and Global
Cereal Fortification Initiative, Tokyo, Japan.
4 Abbreviations used: CV, coefficient of
variation; FAO, Food and Agriculture Organization; IAA, indispensable
amino acids; IDECG, International Dietary Energy Consultative Group;
MIT, Massachusetts Institute of Technology; UN, United Nations; UNU,
United Nations University; WHO, World Health Organization.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONNitrogen (protein) requirementsRequirements for indispensable...Massachusetts Institute of...Importance of revised...REFERENCES |
|---|
1. Basile A., Beaumier L., El-Khoury A., Kenneway M., Gleason R. E., Young V. R. Twenty-four hour L-[1-13C]tyrosine and L-[3–3-2H2]phenylalanine oral tracer studies at generous, intermediate and low phenylalanine intakes to estimate aromatic amino acid requirements in adults. Am. J. Clin. Nutr. 1998;67:640-659[Abstract]
2.
Basile-Filho A., El-Khoury A. E., Beaumier L., Wang S. Y., Young V. R. Continuous twenty-four hour L-[1-13C]phenylalanine and L-[3,3-2H2]tyrosine oral tracer studies at an "intermediate" phenylalanine intake to estimate requirements in adults. Am. J. Clin. Nutr. 1997;65:473-478
3. Bergner H., Simon O., Adams K. Determination of lysine requirement in growing rats based on catabolism rate of 14C- and 15N-labeled lysine. Arch. Tierernahrung 1978;28:21-29
4. Brookes I. M., Owens F. N., Brown R. E., Garrigus U. S. Influence of amino acid level in the diet upon amino acid oxidation by the rat. J. Nutr. 1972;102:27-36
5. Brookes I. M., Owens F. N., Brown R. E., Garrigus U. S. Amino acid oxidation and plasma amino acid levels in sheep with abomasal infusion of graded amounts of lysine. J. Anim. Sci. 1973;36:950-970
6.
Campbell W. W., Crim M. C., Dallal G. E., Young V. R., Evans W. J. Increased protein requirements in elderly people: new data and retrospective reassessments. Am. J. Clin. Nutr. 1994;60:501-509
7. Campbell W. W., Evans W. J. Protein requirements of elderly people. Eur. J. Clin. Nutr. 1996;50(suppl 1):S180-S185
8. Dewey K. G., Beaton G., Fjeld C., Lonnerdal B., Reeds P., with input from Brown K. H., Heinig M. J., Ziegler E., Räihä N.C.R., Axelsson I.E.M. Protein requirements of infants and children. Eur. J. Clin. Nutr. 1996;50(suppl 1):S119-S150
9.
Duncan A. M., Ball R. O., Pencharz P. B. Lysine requirement of adult males is not affected by decreasing dietary protein. Am. J. Clin. Nutr. 1996;64:718-725
10. El-Khoury A. E., Basile A., Beaumier L., Wang S. Y., Al-Amiri H. A., Selvaraj A., Wong S., Atkinson A., Ajami A., Young V. R. Twenty-four hour intravenous and oral tracer studies with L-[1-13C]-2-aminoadipic acid and L-[1-13C]lysine as tracers at generous nitrogen and lysine intakes in healthy adults. Am. J. Clin. Nutr. 1998;68:827-839[Abstract]
11.
El-Khoury A. E., Fukagawa N. K., Sánchez M., Tsay R. H., Gleason R. E., Chapman T. E., Young V. R. Validation of the tracer-balance concept with reference to leucine: 24h intravenous tracer studies with L-[1-13C]leucine and [15N]urea. Am. J. Clin. Nutr. 1994a;59:1000-1011
12.
El-Khoury A. E., Fukagawa N. K., Sánchez M., Tsay R. H., Gleason R. E., Chapman T. E., Young V. R. The 24h pattern and rate of leucine oxidation, with particular reference to tracer estimates of leucine requirements in healthy adults. Am. J. Clin. Nutr. 1994b;59:1012-1020
13. El-Khoury, A. E., Pereira, P. C. M., Borgonha, S., Basile-Filho A., Beaumier, L., Wang, S. Y., Metges, C. C., Ajami, A. M. & Young, V. R. (2000) Twenty-four hour oral tracer studies with L-[1-13C]lysine at a low (15 mg · kg-1 · day-1) and intermediate (29 mg·kg-1·day-1)lysine intake in healthy adults. Am. J. Clin. Nutr. (in press).
14.
El-Khoury A. E., Sánchez M., Fukagawa N. K., Gleason R. E., Tsay R. H., Young V. R. The 24h kinetics of leucine oxidation in healthy adults receiving a generous leucine intake via three discrete meals. Am. J. Clin. Nutr. 1995;62:579-590
15. FAO/WHO (1991) Protein Quality Evaluation: Report of a Joint FAO/WHO Expert Consultation. Paper No. 51. Food and Agriculture Organization of the United Nations, Rome.
16. FAO/WHO/UNU (1985) Energy and Protein Requirements: Report of an FAO/WHO/UNU Expert Consultation. WHO Tech. Rept. Ser. No. 724. World Health Organization, Geneva.
17. Fereday A., Gibson N., Cox M., Halliday D., Pacy P. D., Millward D. J. Postprandial protein utilization in normal adults, II: milk protein measured in the non-steady state. Proc. Nutr. Sci. 1995;54:63A(abs.)
18. Fereday A., Gibson N., Cox M., Halliday D., Pacy P. D., Millward D. J. Postprandial protein utilization of wheat protein from a single meal in normal adults. Proc. Nutr. Soc. 1997a;56:90A(abs.)
19. Fereday A., Gibson N. R., Cox M., Pacy P. J., Millward D. J. Protein requirements and ageing: metabolic demand and efficiency of utilization. Br. J. Nutr. 1997b;77:685-702[Medline]
20. Fomon S. J., Filer L. T., Jr Amino acid requirements for normal growth. Nyhan W. L. eds. Amino Acid Metabolism and Genetic Variation 1967:391-402 McGraw-Hill New York.
21. Fukagawa N. K., Yu Y.-M., Young V. R. Methionine-cysteine kinetics at different intakes of methionine and cystine in elderly men and women. Am. J Clin. Nutr. 1998;68:380-388[Abstract]
22. Holt L. E., Jr, Snyderman S. E. Protein and amino acid requirements of infants and children. Nutr. Abstr. Rev. 1965;37:1-13
23. Irwin M. I., Hegsted D. M. A conspectus of research on amino acid requirements of man. J. Nutr. 1971;101:539-566
24. Jones E. M., Bauman C. A., Reynolds M. S. Nitrogen balances of women maintained on various levels of lysine. J. Nutr. 1956;60:549-559
25. Kurpad A. V., El-Khoury A. E., Beaumier L., Srivatsa A., Kuriyan R., Raj T., Borgonha S., Ajami A. M., Young V. R. An initial assessment, using 24 hour 13C-leucine kinetics, of the lysine requirement of healthy adult Indian subject. Am. J. Clin. Nutr. 1998;67:58-66[Abstract]
26. Millward D. J. The nutritional value of plant-based diets in relation to human amino acid and protein requirements. Proc. Nutr. Soc. 1999;58:249-260[Medline]
27. Millward D. J. Post-prandial protein utilization: implications for clinical nutrition. Proteins, Peptides and Amino Acids in Enteral Nutrition. Proceedings of 3rd Nestlé Nutrition Workshop, Stockholm, Sweden, Sept. 9–10, 1999 2000in press
28. Millward D. J. Can we define indispensable amino acid requirements and assess protein quality in adults?. J. Nutr 1994;124:1509-1516
29.
Millward D. J., Fereday A., Gibson N., Pacy P. J. Aging, protein requirements, and protein turnover. Am. J. Clin. Nutr. 1997;66:774-786
30. Millward D. J., Roberts S. B. Protein requirements of older individuals. Nutr. Res. Rev. 1996;9:67-87
31. Nakagawa I., Takahashi T., Suzuki T., Kobayashi K. Amino acid requirements of children: nitrogen balance at the minimal level of essential amino acids. J. Nutr. 1964;83:115-118
32. Pellett P. L., Young V. R. Role of meat as a source of protein and essential amino acids in human protein nutrition. Pearson A. M. Dutson T. R. eds. Meat and Health: Advances in Meat Research 1990;Vol. 6:329-370 Elsevier Science Publishing New York.
33. Pineda O., Torun B., Viteri F. E., Arroyave G. Protein quality in relation to estimates of essential amino acid requirements. Bodwell C. E. Adkins J. S. Hopkins D. T. eds. Protein Quality in Humans: Assessment and In Vitro Estimation 1981:29-42 AVI Publishing Westport, CT.
34.
Raguso C., Pereira P., Young V. R. A tracer investigation of the obligatory oxidative amino acid losses in healthy, young adults. Am. J. Clin. Nutr. 1999;70:474-483
35.
Rand W. M., Young V. R. Statistical analysis of N balance data with reference to the lysine requirement in adults. J. Nutr. 1999;129:1920-1926
36.
Reeds P. J. Dispensable and indispensable amino acids for humans. J. Nutr. 2000;130:1835S-1840S
37. Rose W. C. The amino acid requirements of adult man. Nutr. Abstr. Rev. 1957;27:631-667
38.
Sánchez M., El-Khoury A. E., Castillo L., Chapman T. E., Basile A., Beaumier L., Young V. R. Twenty-four hour intravenous and oral tracer studies with L-[1-13C]phenylalanine and L-[3,3-2H2]tyrosine at a tyrosine-free generous phenylalanine intake in adults. Am. J. Clin. Nutr. 1996;63:532-545
39.
Sánchez M., El-Khoury A. E., Castillo L., Chapman T. E., Young V. R. Phenylalanine and tyrosine kinetics in young men throughout a continuous 24h period, at low phenylalanine intake. Am. J. Clin. Nutr. 1995;61:555-570
40. Sikka K. C., Johari R. P., Duggan S. K., Ahuja V. P., Austin A. Comparative nutritive value and amino acid content of different extractions of wheat. Agri. Food Chem. 1975;23:24-26
41. Torun B., Pineda O., Viteri F. E., Arroyave G. Use of amino acid composition data to predict protein nutritive value for children with specific reference to new estimates of their essential maino acid requriements. Bodwell C. E. Adkins J. S. Hopkins D. T. eds. Protein Quality in Humans: Assessment and In Vitro Estimations 1981:374-393 AVI Publishing Westport, CT.
42. Williams W. H., Harper A. E., Hegsted D. M., Arroyave G., Holt L. E., Jr Nitrogen and amino acid requirements. Committee on Amino Acids/Food and Nutrition Board/National Research Council eds. Improvement of Protein Nutriture 1974:l23-l163 National Academy of Sciences Washington, D.C.
43. Working Group Clugston, G., Dewey, K. C., Fjeld, C., Millward, J., Reeds, P., Scrimshaw, N. S., Tontisirin, K., Waterlow, J. C. & Young, V. R. Report of a working group on protein and amino acid requirements. Eur. J. Clin. Nutr. 1996;50(suppl 1):S193-S195
44. World Health Organization World Health Report: Executive Summary: Life in 21st Century—A Vision for All 1998 World Health Organization Geneva. http//www.who.int/whr/1998/whr-en.htm
45. Young V. R. Nutrient interactions with reference to amino acid and protein metabolism in non-ruminants: particular emphasis on protein-energy relations in man. Zeit. Ernahrungswissenschaft 1991;30:239-267
46. Young V.R. Macronutrient needs in the elderly. Nutr. Rev. 1992;50:454-462[Medline]
47. Young V. R. Amino acid flux and requirements: counterpoint: tentative estimates are feasible and necessary. Committee on Military Nutrition/Food and Nutrition Board/Institute of Medicine eds. The Role of Protein and Amino Acids in Sustaining and Enhancing Performance 1999:217-242 National Academy Press Washington, D.C.
48. Young V. R., Ajami A. M. Glutamate: an amino acid of particular distinction. J. Nutr. 2000;130:892S-900S
49.
Young V. R., Bier D. M., Pellett P. L. A theoretical basis for increasing current amino acid requirements in adult men, with experimental support. Am. J. Clin. Nutr. 1989;50:80-96
50.
Young V. R., El-Khoury A. E. Can amino acid requirements for nutritional maintenance in adult humans be approximated from the amino acid composition of body mixed proteins?. Proc. Natl. Acad. Sci. U.S.A. 1995;92:200-304
51. Young V. R., El-Khoury A. E. Human amino acid requirements: a re-evaluation. Food Nutr. Bull. 1996;17:191-203
52.
Young V. R., El-Khoury A. E., Raguso C. A., Forslund A. H., Hambraeus L. Urea production, hydrolysis and leucine oxidation change linearly over widely varying protein intakes in healthy adults. J. Nutr. 2000;130:761-766
53. Young V. R., Fajardo L., Murray E., Rand W. M., Scrimshaw N. S. Protein requirements of man: comparative nitrogen balance response within the submaintenance-to-maintenance range of intake of wheat and beef proteins. J. Nutr. 1975;105:534-542
54. Young V. R., Gersovitz M., Munro H. N. Human aging: protein and amino acid metabolism and implications for protein and amino acid requirements. Moment G. B. eds. Nutritional Approaches to Aging Research 1982:47-81 CRC Press Boca Raton, FL.
55.
Young V. R., Marchini J. S. 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;51:270-289
56.
Zello G. A., Pencharz P. B., Ball R. O. The dietary lysine requirement of adult males determined by the oxidation of an indicator amino acid L-[1-13C]phenylalanine. Am. J. Physiol. 1993;264:E677-E685
This article has been cited by other articles:
|
|
 |
|
  Y. Ingenbleek The Nutritional Relationship Linking Sulfur to Nitrogen in Living Organisms J. Nutr., June 1, 2006; 136(6): 1641S - 1651S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. K. Fukagawa Sparing of Methionine Requirements: Evaluation of Human Data Takes Sulfur Amino Acids Beyond Protein J. Nutr., June 1, 2006; 136(6): 1676S - 1681S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. C. G. van de Poll, C. H. C. Dejong, and P. B. Soeters Adequate Range for Sulfur-Containing Amino Acids and Biomarkers for Their Excess: Lessons from Enteral and Parenteral Nutrition J. Nutr., June 1, 2006; 136(6): 1694S - 1700S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. V. Kurpad, M. M. Regan, T. Raj, and J. V. Gnanou Branched-Chain Amino Acid Requirements in Healthy Adult Human Subjects J. Nutr., January 1, 2006; 136(1): 256S - 263S. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-P. Bonjour Dietary Protein: An Essential Nutrient For Bone Health J. Am. Coll. Nutr., December 1, 2005; 24(suppl_6): 526S - 536S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. R. Rodriguez Optimal Quantity and Composition of Protein for Growing Children J. Am. Coll. Nutr., April 1, 2005; 24(2): 150S - 154S. [Abstract] [Full Text] [PDF]
|
|
|
|
