Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005) / Chapter Skim
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10. Protein and Amino Acids
10. Protein and Amino Acids
Pages 589-768
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From page 589... ...
For amino acids, isotopic tracer methods and linear regression analysis were used whenever possible to determine the requirements. The estimated average requirements for amino acids were used to develop amino acid scoring patterns for various age groups based on the recommended intake of dietary protein.
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Proteins are macromolecules consisting of long chains of amino acid subunits. The structures for the common L-amino acids found in typical dietary proteins are shown in Figure 10-1.
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From page 591... ...
FIGURE 10-1 L-amino acids of nutritional significance.
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From page 592... ...
Histidine and amino acids with the carboxyl side chains (glutamic acid and aspartic acid) are critical features in ion-binding proteins, such as the calcium-binding proteins (e.g., troponin C)
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From page 593... ...
Five of the amino acids in Table 10-1 are termed dispensable as they can be synthesized in the body from either other amino TABLE 10-1 Indispensable, Dispensable, and Conditionally Indispensable Amino Acids in the Human Diet Conditionally Precursors of Conditionally Indispensable Dispensable Indispensablea Indispensable Histidineb Alanine Arginine Glutamine/glutamate, asparate Isoleucine Aspartic acid Cysteine Methionine, serine Leucine Asparagine Glutamine Gl utamic acid/ammonia Lysine Glutamic acid Glycine Serine, choline Methionine Serine Proline Glutamate Phenylalanine Tyrosine Phenylalanine Threonine Tryptophan Valine aConditionally indispensable is defined as requiring a dietary source when endogenous synthesis cannot meet metabolic need. bAlthough histidine is considered indispensable, unlike the other eight indispensable amino acids, it does not fulfill the criteria used in this report of reducing protein deposition and inducing negative nitrogen balance promptly upon removal from the diet.
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From page 594... ...
. The mixture of dispensable and conditionally indispensable amino acids as supplied by food proteins at adequate intakes of total nitrogen will assure that both the nitrogen and specific amino acid needs are met.
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. Thus, the immediately accessible stores of protein (which serve as the source of indispensable amino acids and amino nitrogen)
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From page 596... ...
There is a wide range of variation in daily dietary protein intake, from the protein requirement and beyond, to which the body is able to adapt over a period of days, after which no further change in body protein content occurs. However, pathological conditions, such as severe disease states, can cause substantial rates of protein loss due to the increased demand for either amino acids or carbon skeletons to meet local energy demands.
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From page 597... ...
. The other major pathways that involve the free amino acid pool are the supply of amino acids by the gut from the absorbed amino acids derived from dietary proteins, the de novo synthesis in cells (including those of the gut, which are a source of dispensable amino acids)
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From page 598... ...
, and although the present recommendations for the dietary amino acids for infants provided in this report continue to be based on human milk as the standard, recent authors (Dewey et al., 1996) have cautioned that the composition of human milk proteins is not necessarily a definition of the biological amino acid requirements of the growing neonate.
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From page 599... ...
For example, the indispensable amino acid requirements for adults may provide a quarter of their minimum total need for amino nitrogen, compared with the need for noncollagen body protein in which approximately half of the amino acids are indispensable (FAO/WHO/UNU, 1985)
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From page 600... ...
is high, there is now good evidence to show that nutritionally significant quantities of indispensable amino acids are metabolized by the tissues of the splanchnic bed, including the mucosal cells of the intestine (Fuller and Reeds, 1998)
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From page 601... ...
molecules, which are synthesized in the nucleus from regions of DNA by the process of transcription. The mRNA molecules then interact with various tRNA molecules attached to specific amino acids in the cytoplasm to synthesize the specific protein by linking together individual amino acids; this process, known as translation, is regulated by amino acids (e.g., leucine)
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From page 602... ...
Protein Degradation The mechanism of intracellular protein degradation, by which protein is hydrolyzed to free amino acids, is more complex and is not as well characterized at the mechanistic level as that of synthesis (Kirschner, 1999)
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From page 603... ...
Amino Acid Catabolism Nitrogen Metabolism About 11 to 15 g of nitrogen are excreted each day in the urine of a healthy adult consuming 70 to 100 g of protein, mostly in the form of urea, with smaller contributions from ammonia, uric acid, creatinine, and some free amino acids (Table 10-4)
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From page 604... ...
Most amino acids can take part in these reactions, with the result that their amino nitrogen is transferred to just three amino acids: alanine from pyruvate, aspartate from oxaloacetate, and glutamate from -ketoglutarate. Unlike many amino acids, branched-chain amino acid transamination occurs throughout the body, particularly in skeletal muscle.
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From page 605... ...
Carbon Metabolism For most amino acids, removal of the amino nitrogen group generates their ketoacid analogues. Many of these are already in a form for entry into the pathways of oxidative metabolism (Figure 10-3)
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From page 606... ...
If they enter as acetyl-CoA, then only fat or ketone bodies can be formed. The carbon skeletons of other amino acids can, however, enter the pathways in such a way that their carbons can be used for gluconeogenesis.
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From page 607... ...
The cycle involving glutamine transport from the periphery to the gastrointestinal tract is also vital to the synthesis of arginine and proline and is critical to the prevention of the build up of excessive ammonia in the circulation. Nonprotein Pathways of Amino Acid Nitrogen Utilization Although in general the utilization of dietary amino acids is dominated by their incorporation into protein and their role in energy metabolism, amino acids are also involved in the synthesis of other nitrogenous compounds important to physiological viability as shown in Table 10-5.
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From page 608... ...
. Similarly, unless amino acids are present in the diet in the right balance (see later section, "Protein Quality")
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Borderline inadequate protein intakes in infants and children are reflected in failure to grow as estimated by length or height (Jelliffe, 1966; Pencharz, 1985)
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This section reviews some of the possible indicators used or proposed for use in analyses estimating human protein requirements. Factorial Method The factorial method is based on estimating the nitrogen (obligatory)
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From page 611... ...
needs, high-quality proteins are utilized as test proteins to prevent negative nitrogen balance resulting from the inadequate intake of a limiting indispensable amino acid. A significant literature exists regarding the methods and procedures to use in determining nitrogen balance amount (Manatt and Garcia, 1992; Rand et al., 1981)
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From page 612... ...
To some extent, this assumption poses problems that may lead to underestimates of the true protein requirement. First, there are sufficient observations of paradoxically high positive nitrogen balances in the literature to imply that when individuals are in measured body nitrogen equilibrium, they are in fact in a small negative nitrogen balance (Kopple, 1987)
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From page 613... ...
were derived from the analysis of protein requirements. SELECTION OF INDICATORS FOR ESTIMATING THE REQUIRMENT FOR INDIVIDUAL AMINO ACIDS Irrespective of whether a design involving multiple studies in a limited number of individuals or single studies in a larger number of subjects has been used, the uniform approach to the determination of the requirement for an individual indispensable amino acid involves measuring the relationship between the intake of the amino acid (in an otherwise adequate diet)
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From page 614... ...
In fact, within the large nitrogen balance and amino acid requirement literature, only one other study (Reynolds et al., 1958) was found in which adults were studied at four or more different intakes of amino acids with constant levels of total nitrogen (Reynolds et al., 1958)
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From page 615... ...
Direct Amino Acid Oxidation (DAAO) Method In the 1980s, Young and his coworkers introduced the use of measurements of the carbon oxidation of single indispensable amino acids as indicators of adequacy of the amino acids (Young et al., 1989)
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From page 616... ...
The second limitation is that the DAAO method can only be used with full accuracy for those amino acids whose carboxyl group is released directly to the body bicarbonate pools. This limits its use largely to the branched chain amino acids, phenylalanine, and lysine.
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From page 617... ...
as a carbon analogue of nitrogen balance. The reasoning is that when a single indispensable amino acid is provided below its requirement, it acts as the single and primary limitation to the ability to retain other nonlimiting amino acids in body protein.
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From page 618... ...
Thus amino acids such as threonine, whose peculiar metabolism makes them problematical in the DAAO method, can be studied. Second, the pool size of the indicator amino acid does not change radically as the intake of the test amino acid is varied.
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From page 619... ...
On the other hand, if the individual only needs to be on a low or even zero intake of the test amino acid for a matter of 8 hours, then it becomes feasible to study indispensable amino acids in these and other vulnerable groups. Such a minimally invasive indicator oxidation model has been developed (Bross et al., 1998)
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From page 620... ...
. These nonprotein nitrogenous components include free amino acids, pyrimidine nucleotides, creatine, and glutathione, but the large majority is urea.
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From page 621... ...
. It is recognized that casein and whey in cow milk is not the same as human casein and whey and that the absorption and digestibility of amino acids from formula is different than that of human milk.
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From page 622... ...
622 milk analysis analysis analysis assay reaction approximated Kjeldahl Kjeldahl Kjeldahl multiplying Biuret was by by 6.25 by by by dye-binding the by by content figure determined determined nitrogen determined sample study determined analyzed analyzed Canada protein from protein Comments Milk Nitrogen Nitrogen Protein Nitrogen Protein Protein Mid-feed and a States Content (g/dL) 0.08 0.09 0.04 0.05 0.20 0.16 0.16 0.24 0.17 0.36 0.06 ± ± ± ± 0.6 0.2 0.4 ± ± ± ± ± ± ± United Milk ± ± ± (SEM)
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623 g/L assay 7 milk milk milk months analysis analysis analysis 11. Lowry Lowry as ring du milk Kjeldahl Kjeldahl Kjeldahl multiplying g/L modified by 6.25 multiplying by 6.25 multiplying by 6.25 modified a by by by by by by a human 12.3 by by of as milk determined nitrogen determined nitrogen determined nitrogen analyzed determined determined determined analyzed content human of protein protein protein assay protein Protein Nitrogen Protein Nitrogen Protein Nitrogen Protein Protein content average protein 0.27 0.22 0.18 0.16 0.10 0.15 0.16 0.16 0.18 0.10 0.05 0.15 0.15 0.18 0.15 estimate ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± to average (SEM)
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From page 624... ...
estimates of the maintenance requirement, which is determined by regression analysis of the relationship between nitrogen intake and nitrogen balance, (2) measurement of the rates of protein deposition, which are derived from body composition analysis, and (3)
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From page 625... ...
Individual maintenance protein requirements were estimated by first regressing nitrogen balance on nitrogen intake for the individuals studied at several different intake levels, and then using these individual regression equations to interpolate the intakes that would be expected to produce zero nitrogen balance (adjusting for 6.5 mg/kg/d for miscellaneous losses)
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From page 626... ...
Estimates of rates of protein deposition for infants from 9 months through 3 years of age (Butte et al., 2000) and total body protein content from 4 through 18 years of age (Ellis et al., 2000)
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To obtain protein deposition rates since the data in young children were longitudinal (Butte et al., 2000) , and the data in older children were cross-sectional (Ellis et
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Girls protein content = 0.00027 × age (y)
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From page 629... ...
+ (1.72 [efficiency of protein utilization derived from reciprocal of slope in Table 10-8] × mean protein deposition for life stage and gender group)
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2) , where CVM is 0.12, the maintenance requirement is 0.688 g protein/kg/d, CVG is 0.43, and the growth requirement is the rate of protein deposition divided by the efficiency of dietary protein utilization.
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From page 631... ...
EAR for Boys and Girls 13 years 0.87 g/kg/d of protein2 48 years 0.76 g/kg/d of protein 913 years 0.76 g/kg/d of protein Protein RDA Summary, Ages 1 Through 13 Years Assuming the variation of maintenance requirements for protein and protein deposition requirements vary, then the RDA is set as indicated at the 97.5th percentile, estimated as follows: RDA = EAR + 2 ( [0.12 × 0.688 g protein/kg/d] 2 + [0.43 × 1.72 × Y g protein/kg/d]
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From page 632... ...
is similar to that for adults (105 mg/kg/d as shown in Table 10-12) , the EAR for adolescents 14 through 18 years of age is based on the adult estimates of maintenance requirements from nitrogen balance studies (Rand et al., 2003)
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From page 633... ...
RDA for Boys 1418 years 0. 85 g/kg/d of protein or 52 g/d of protein RDA for Girls 1418 years 0.85 g/kg/d of protein or 46 g/d of protein Adults Ages 19 Through 50 Years Evidence Considered in Estimating the Average Requirement In adults, protein requirement estimates have depended on one of two main approaches, namely, the factorial method and nitrogen balance response to different levels of intake of defined quality protein intakes.
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From page 634... ...
included 19 studies conducted across the globe that measured and published nitrogen balance responses for 235 individuals given at least three levels of nitrogen intake for periods of 10 to 14 days (to be included in the analysis, it was required that individual data be available for at least three levels of intake adapted to by consuming the diet for least 10 days, with urinary and fecal nitrogen collection in the final 5 days of the diet period)
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From page 635... ...
However, as discussed in earlier sections, the efficiency of utilization of dietary protein declines as nitrogen equilibrium is reached. More recent approaches have averaged nitrogen balance data obtained from various studies where healthy individuals were given highquality protein sources so that total nitrogen is considered the limiting dietary component rather than a specific indispensable amino acid (FAO/ WHO/UNU, 1985)
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From page 636... ...
636 47 35 Nitrogen = = 54 50 Endogenous of N/kg/d) = 52 = 47 = = 100 Total Loss (mg ~ Men Women All Men Women All Losses Obligatory Miscellaneous N/kg/d)
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in a trimmed data set showing the skewness of protein requirement. SOURCE: William Rand, personal communication, 2002.
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638 0 at 45)
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. Statistical Analysis of Nitrogen Balance Data to Determine the Protein Requirement Data Analysis.
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From page 640... ...
640 a Nitrogen 0.27 0.97 0.62 0.72 0.29 Mann- Median Requirement (mg/kg/d) 102 101 111 102 111 102 102 101 104 102 103 101 111 and Medians dian 0.020 0.23 0.27 0.83 0.002 Me Intercept (mg/kg/d)
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From page 641... ...
641 0.98 0.94 0.64 0.047 0.401 0.001 0.62 91 103 111 103 103 101 108 105 105 103 113 104 131 109 < 104 107 104 0.27 0.40 0.40 0.011 0.025 0.20 0.81 47.0 36.7 47.6 39.2 40.6 45.0 50.5 48.1 45.3 51.9 49.4 36.7 49.4 43.1 48.8 49.4 46.6 0.48 0.31 0.18 0.48 0.44 0.47 0.46 0.50 0.47 0.85 0.47 0.45 0.50 0.20 0.48 0.31 0.003 0.46 0.47 0.47 0.46 0.47 0.48 0.62 2 9 43 36 17 13 15 81 14 54 64 77 94 235 154 221 181 requirement. Young Old P-value Male Female P-value Animal Vegetable Mixed P-value All Temperate Tropical P-value Young Old P-value Male Female P-value Animal Vegetable Mixed P-value ×nitrogen 6.25 = requirement data Age Gender Diet Climate Age Gender Diet Protein All a
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From page 642... ...
al., 2003) , a separate analysis was conducted to evaluate the extent to which the four factors thought to have the most influence on protein requirements -- climate, age, gender, and dietary protein source -- were analyzed.
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From page 643... ...
. Other Approaches to Determine the Protein Requirement Based on the Recent Meta-Analysis In addition to the linear statistical approach to determine protein requirements described in detail above, the authors considered three other statistical approaches to the nitrogen balance analysis (Rand et al., 2003)
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From page 644... ...
EAR for Men 1930 years 0.66 g/kg/d of protein 3150 years 0.66 g/kg/d of protein EAR for Women 1930 years 0.66 g/kg/d of protein 3150 years 0.66 g/kg/d of protein Protein RDA Summary, Ages 19 Through 50 Years The RDA for protein is set using the nitrogen balance database and methodology detailed by Rand and colleagues (2003) who demonstrated that the natural logarithm of requirement (in mg nitrogen/kg/day)
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From page 645... ...
This gives a value of 12.5 mg nitrogen/kg/d (CV = 12 percent) which can be used to estimate the RDA's of other age groups and for individual amino acids where fewer data from the following formula: RDA = EAR + 2 CV, or RDA = 1.24 × EAR.
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From page 646... ...
involved a direct comparison of old with young adults; however, the authors made no assessment of the miscellaneous nitrogen losses and were not able to show any clear difference in the requirement of older and younger adults. In inter TABLE 10-14 Nitrogen Balance Studies in Older Individuals Protein Intake Reference Study Population Levels (g/kg/d)
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From page 647... ...
32 (varied) 0.780.82 -- < 0.92 bEnergy intake was either held constant for duration of nitrogen balance period, or varied to maintain body weight; varied levels are average intakes of group as reported by authors.
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From page 648... ...
. All the data from studies of nitrogen balance in the older adults were included in the regression procedure employed to determine the protein requirement of adults 19 to 50 years of age, and no significant effect of age in terms of the amount of protein required per kilogram of body weight was detected (Table 10-13)
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From page 649... ...
. It can thus be assumed as with younger adults percent that the RDA = EAR + 2 CV for protein and individual amino acids, or RDA = 1.24 × EAR.
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From page 650... ...
and as noted previously (see "Nitrogen Balance Methods") , at high nitrogen intakes erroneous positive nitrogen balances have frequently been obtained.
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From page 651... ...
(g/d) a MacGillivray and 6 3.22 19.3 9.4 Buchanan, 1958 King et al., 1973 10 3.41 34.1 9.9 Emerson et al., 1975 5 3.43 17.2 10.0 Pipe et al., 1979 27 1.78 48.1 5.2 Forbes, 1987 50 2.64 132 7.7 Forsum et al., 1988 22 2.13 48.9 6.2 Total 120 297.9 Mean 2.48b 7.2 a Protein deposition = Total potassium accumulated (mmol/d)
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From page 652... ...
. Closer review of the data indicates that for those six adolescents who demonstrated a positive efficiency at multiple levels of protein intake, the mean of the slope of the positive nitrogen balances was 0.43 ± 0.21 (median = 0.44)
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From page 653... ...
653 f and adults.
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From page 654... ...
Protein EAR Summary, Pregnancy Based upon the nitrogen balance study of King and coworkers (1973) and the estimated average protein deposition during pregnancy based on
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From page 655... ...
Since this figure includes the protein needs for the additional tissue deposited, when calculating the amount needed per kilogram of body weight to use with pregnant women, only the amount needed for protein deposition is considered. Thus the increased amount on a bodyweight basis is +12.6 g of protein/d ÷ 57 kg (reference woman)
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From page 656... ...
No study could be found that investigated dietary protein intervention in twin pregnancy. On the basis of these data, it seems prudent to provide women carrying twins with protein intakes of an additional 50 g/d beginning in the second trimester, along with sufficient energy to utilize the protein as efficiently as possible.
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From page 657... ...
In this approach, it is assumed that the process of lactation does not alter the maintenance protein requirement of the nonlactating woman and that the protein and amino acid requirements are increased in proportion to milk production. It is important to emphasize that human milk is characterized by a relatively high concentration of nonprotein nitrogenous substances, which contribute approximately 20 to 27 percent of total milk nitrogen (Butte et al., 1984a, 1984b; Dewey et al., 1996)
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From page 658... ...
658 fmilko older and Lactation e y ag 18 of equivalent with > 23.4 21.9 21.3 18.3 21.2 Protein years in protein 19 (g/d)
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From page 659... ...
So, 1.24 multiplied by the EAR of + 21 g of protein/d = +26 g; rounded to the nearest 5 g/d, the RDA = +25 g/d. Again, in considering the amount needed per kg of body weight, the increase in the RDA is calculated as the EAR of +21 g/d × 1.24 ÷ 54 kg (reference weight)
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From page 660... ...
Endurance Training. Endurance training does not result in muscle building, which would increase muscle protein deposition, but it is well recognized that endurance exercise is accompanied by an increase in the oxidation of branched chain amino acids (Lemon et al., 1982, 1985; Rennie et al., 1981; Wagenmakers, 1998; White and Brooks, 1981)
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From page 661... ...
. Individuals who restrict their diet to plant foods may be at risk of not getting adequate amounts of certain indispensable amino acids because the concentration of lysine, sulfur amino acids, and threonine are sometimes lower in plant food proteins than in animal food proteins (FAO/WHO/UNU, 1985)
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From page 662... ...
In conclusion, available evidence does not support recommending a separate protein requirement for vegetarians who consume complementary mixtures of plant proteins. FINDINGS BY LIFE STAGE AND GENDER GROUP FOR INDISPENSABLE AMINO ACIDS The original technique used to determine amino acid requirements in individuals studied with graded levels of intake of the test amino acid was nitrogen balance (see "Nitrogen Balance Method")
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From page 663... ...
Indispensable Amino Acids AI Summary, Ages 0 Through 6 Months The AI for infants 0 through 6 months of age is based on the average volume of milk intake of 0.78 L/d (Allen et al., 1991; Heinig et al., 1993) , and the mean indispensable amino acid content of human milk (Table 10-18)
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From page 664... ...
Children Ages 7 Months Through 18 Years Evidence Considered in Estimated the Average Requirement Nitrogen Balance. The only data derived directly from experiments to determine the indispensable amino acids requirements of children have been obtained by studying nitrogen balance.
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From page 665... ...
on Japanese boys 10 to 12 years of age. Although these data seem to be accurate as there was uniformly negative nitrogen balance when the test amino acid was at zero, the maximum rate of nitrogen retention found when the amino acids were given in adequate quantities was 33 ± 14 mg/kg/d.
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From page 666... ...
. This was then converted to a dietary requirement for protein deposition by dividing the need by the incremental efficiency of dietary protein utilization, which is estimated by the average slope of the regression analyses evaluating the protein requirement from studies done in children 7 months through TABLE 10-19 Indispensable Amino Acid Composition of Whole Body Protein mg/g Protein ± 1 Standard Deviation Amino Acid (from interspecies comparison)
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From page 667... ...
Thus, the maintenance protein requirement of 688 mg/kg/d (110 mg of N/kg/d for children through age 13 in Table 10-8 × 6.25) can be converted into requirements for individual amino acids by multiplying the maintenance protein requirement by the proportional contribution of the amino acid to body protein (Table 10-19)
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From page 668... ...
668 for of ×6.25 Amino children content estimates for in N/kg/d acid of Requirements the 0.58 EAR by mg amino Ratio Maintenance Acid to -- -- 1.4 1.5 1.5 1.7 1.7 2.0 1.7 110 10-8) the Children utilization, by adults.
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From page 669... ...
. Indispensable Amino Acid EAR and RDA Summary, Ages 7 Months Through 18 Years To calculate a factorial estimate of the EAR for individual indispensable amino acids, the amino acid needs for growth or protein deposition are first calculated as the product of the average rate of protein deposition (Table 10-9)
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From page 670... ...
In the same way, the EARs for each of the indispensable amino acids at different age groups were calculated and the results are shown in Table 10-21. The RDA for the indispensable amino acids for children is set by determining the coefficients of variation for maintenance and for protein deposition.
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From page 671... ...
As shown in Table 10-22, 24-hour amino acid balance studies have been completed for four amino acids: leucine (El-Khoury et al., 1994a; Kurpad et al., 2001b) , lysine (Kurpad et al., 2001a, 2002a)
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From page 672... ...
and 22 30 65 62 30 9 58 34 39 16 22 48 45 22 41 24 6 28 Through (EAR) b Months 7 Deposition Acid Requirement Ages Amino (mg/kg/d)
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From page 673... ...
673 continued 16 22 49 46 22 41 24 6 28 17 22 49 46 22 41 24 6 28 13 18 40 37 18 33 19 5 23 13 18 40 37 18 33 19 5 23 1 2 4 3 2 3 2 1 2 1 2 4 4 2 4 2 1 42 11 15 34 31 4 15 27 16 19 11 15 34 31 4 15 27 16 19 tyrosine tyrosine cysteine + cysteine + + + Girls Boys Boys, y, y, Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine 48 913
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From page 674... ...
674 d RDA (mg/kg/d) 15 21 47 43 21 38 22 6 27 15 21 47 43 21 38 22 6 27 c EAR = Total (mg/kg/d)
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From page 675... ...
675 of x + EAR = deposition composition 1418y 14 19 44 40 19 35 5 21 24 acid acid ages amino for ×amino + RDA ]
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From page 676... ...
However, from a practical point of view, the 24-hour amino acid balance studies are very labor intensive with the result that only three or four levels of intake of the test amino acid have been studied for each of leucine, lysine, phenylalanine + tyrosine, and threonine. Direct Amino Acid Oxidation.
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From page 677... ...
Table 10-22, DAAO studies of indispensable amino acid requirements are limited to leucine (Meguid et al., 1986a) , lysine (Meredith et al., 1986)
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From page 678... ...
IAAO has the advantage that the requirement of any amino acid can be determined, since either phenylalanine (in the presence of an excess of tyrosine to ensure that there is no label retention in the body tyrosine pools) or lysine can and have been used as indicator amino acids in humans and in animals (Bross et al., 2000; Brunton et al., 1998; Zello et al., 1995)
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From page 679... ...
Indispensable Amino Acid EAR Summary, Ages 19 Years and Older An EAR was derived for each of the indispensable amino acids from the data in Table 10-22. Where more than one EAR was given for an amino acid in Table 10-22, the values were averaged and rounded to the nearest whole number.
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From page 680... ...
Amino Acid EAR and RDA Summary, Pregnancy EAR for Pregnancy For all ages 15 mg/kg/d of histidine 20 mg/kg/d of isoleucine 45 mg/kg/d of leucine 41 mg/kg/d of lysine 20 mg/kg/d of methionine + cysteine 36 mg/kg/d of phenylalanine + tyrosine 21 mg/kg/d of threonine 5 mg/kg/d of tryptophan 25 mg/kg/d of valine The RDA for amino acids for pregnancy is set by increasing the EAR by the variation in protein derived for adults ages 19 years and older (1.24 × EAR) and rounded to nearest whole number.
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From page 681... ...
. To estimate the EAR for amino acids for lactation, the average amounts of amino acids in human milk during the first 6 months of lactation expressed as mg/kg/d based on the reference weight of the adult woman in Table 1-1 (see "AI for Infants 06 Months")
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From page 682... ...
In practice, protein quality is principally determined by two factors: digestibility and the amino acid composition of the protein in question. In food as opposed to relatively pure protein, the contribution of all of the indispensable amino acids to the total nitrogen content of the food has to be considered in assessing the overall protein quality of the diet.
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From page 683... ...
of amino acids from food protein sources is based on the digestibility of total nitrogen as contrasted to that for the individual amino acid. However, there can be quite large differences between the digestibility coefficients for total nitrogen and the individual amino acid.
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From page 684... ...
However, the major requirement for total nitrogen or protein is for the specific indispensable amino acids (and/or conditionally indispensable amino acids) and an additional source of -amino nitrogen.
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From page 685... ...
Amino Acids Content of Proteins The second and generally more important factor that influences the nutritional value of a protein source is the relative content and metabolic availability of the individual indispensable amino acids. If the content of a single indispensable amino acid in the diet is less than the individual's requirement, then it will limit the utilization of other amino acids and thus prevent normal rates of protein synthesis even when the total nitrogen intake level is adequate.
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From page 686... ...
Amino Acid Scoring and Protein Quality In recent years, the amino acid requirement values for humans have been used to develop reference amino acid patterns for purposes of evaluating the quality of food proteins or their capacity to efficiently meet both the nitrogen and indispensable amino acid requirements of the individual. Based on the estimated average requirements for the individual indispensable amino acids presented earlier (Tables 10-20 and 10-21)
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From page 687... ...
. dBased on 1- to 3-year-old Estimated Average Requirements for protein and indispensable amino acids.
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From page 688... ...
The extent to which the requirements for specific indispensable amino acids and total protein are correlated is not known. In this report it is assumed that the variance in requirement for each indispensable amino acid is the same as that for the adult protein requirement.
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From page 689... ...
For a diet based on a mixture of wheat, chickpea, and skim milk proteins the PDCAAS is 110 percent, which is truncated to a value of 100, since the relative efficiency of utilization of the limiting amino acid cannot be greater than that of the amino acid scoring pattern at nitrogen intakes sufficient to meet nitrogen needs. Finally, it should be noted that PDCAAS scores have only been calculated here based on four indispensable amino acids (lysine, sulfur amino acids, threonine, and tryptophan)
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From page 690... ...
eWeighted values based on the proportion of the total protein in the mixture that is contributed by each protein source. the most likely limiting amino acids in common food protein sources and so have been considered here for illustrative purposes.
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From page 691... ...
obscured these results and illustrate the conservative nature of their meta-analysis of the primary nitrogen balance. Moreover, this discussion and presentation of data in Table 10-27 underscores the fact that while lysine is likely to be the most limiting of the indispensable amino acids in diets based predominantly on cereal proteins, the risk of a lysine inadequacy is essentially removed by inclusion of relatively modest amounts of animal or other vegetable proteins, such as those from legumes and oilseeds, or through lysine fortification of cereal flour.
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From page 692... ...
These changes are part of the normal regulation of the amino acids and nitrogen and represent no hazards per se, at least within the range of intakes normally consumed by apparently healthy individuals. Nonetheless, a number of adverse effects have been reported, especially at the very high intakes that might be achieved with supplement use, but also at more modest levels.
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From page 693... ...
Nitrogen balance studies at protein intakes of 212 to 300 g/d consistently have shown positive nitrogen balance (Fisher et al. 1967; Oddoye and Margen, 1979; Tarnopolsky et al., 1988)
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From page 694... ...
. It is probable that when high protein diets are given, the capacities to oxidize amino acids and synthesize urea are increased, as has been demonstrated in animals (Das and Waterlow, 1974)
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From page 695... ...
· There is no evidence that amino acids derived from usual or even high intakes of protein from foodstuffs present any risk. Therefore, attention was focused on intakes of amino acids from dietary supplements and when utilized as food ingredients, such as monosodium glutamate in food or aspartic acid and phenylalanine in aspartame.
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From page 696... ...
Less emphasis was placed on these studies than those with adequate protein diets because of concern over the creation of amino acid imbalances. · For some well-studied amino acids, there were no adverse effects reported at the highest dose tested in long-term studies.
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From page 697... ...
Arginine L-Arginine is incorporated into tissue proteins, and is required for the synthesis of other amino acids, polyamines, and creatine, as well as for the detoxification of ammonia via the urea cycle (Rodwell, 1990)
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From page 698... ...
reported significantly increased thymus weight, spleen cell mitogenesis, and inducible natural killer cell activity in mice after oral arginine (drinking water) doses of 60, 120, or 240 mg/kg of body weight/d.
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From page 699... ...
DoseResponse Assessment Studies of oral administration of supplemental arginine in humans (in excess of normal dietary intakes of approximately 5.4 g/100 g of mixed dietary proteins) were not designed to systematically study the toxicity of chronic oral exposure to this amino acid.
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From page 700... ...
Therefore, since neither a NOAEL nor LOAEL can be identified for intake of L-arginine from dietary supplements in healthy individuals, a UL could not be determined. Asparagine L-Asparagine is a dispensable amino acid, the amide of the dicarboxylic amino acid aspartic acid that is either deaminated during food processing or converted into aspartate by the mucosal cells.
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From page 701... ...
Based on distribution data from the 1988 1994 NHANES III, mean daily intakes for all life stage and gender groups of aspartic acid from food and supplements are 6.5 g/d (Appendix Table D-4)
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From page 702... ...
Plasma phenylalanine levels doubled over fasting concentrations 45 to 60 minutes after dosing with aspartame but returned to baseline after 4 hours. Plasma concentrations of other amino acids remained unchanged.
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From page 703... ...
In view of the ongoing scientific debate regarding the sensitivity of newborn animals to the consumption of supplemental dicarboxylic amino acids, it is concluded that aspartic acid dietary supplements are not advisable for infants and pregnant women. Although the scientific data are not sufficient to develop a UL for aspartic acid, it should be noted that dietary supplement doses of up to 8 g/d (approximately 120 mg/kg body weight/d)
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From page 704... ...
-- leucine, isoleucine, and valine -- differ from most other indispensable amino acids in that the enzymes initially responsible for their catabolism are found primarily in extrahepatic tissues. Each undergoes reversible transamination, catalyzed by a branched-chain aminotransferase (BCAT)
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From page 705... ...
These amino acids have received considerable attention in efforts to reduce brain uptake of aromatic amino acids and to raise low circulating levels of BCAA in patients with chronic liver disease and encephalopathy (LSRO, 1992; Marchesini et al., 1990; Skeie et al., 1990)
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From page 706... ...
These trials measured physical and mental performance, the impact on blood levels of other amino acids, and in one case, of insulin and glucose output. Although some evidence of reduced muscle catabolism and clear evidence of an impact on blood concentrations of other amino acids (most especially, declines in the other BCAA and several other neutral amino acids)
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From page 707... ...
In another study, BCAA dosing lowered plasma and brain concentrations of all indispensable amino acids, but there appeared to be no consistent association of these alterations with protein selection (Anderson et al., 1990)
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From page 708... ...
In this case, both dose levels of both amino acids significantly increased bladder carcinoma incidence over groups receiving BHBN alone or groups receiving amino acids alone (see Table 10-28)
|
From page 709... ...
may reduce fetal body weight and relative brain weights and cause sharp increases in brain concentrations of certain amino acids. Thoemke and Huether (1984)
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From page 710... ...
In one study, insulin sensitivity was increased by BCAA supplementation. The effects of BCAA on plasma and whole blood concentrations of amino acids have been convincingly and repeatedly observed under a variety of conditions in experimental animal studies.
|
From page 711... ...
It is interconvertible to cystine, and for purposes of this report, L-cysteine and L-cystine are considered together. Based on distribution data from the 19881994 NHANES III, the mean daily intake for all life stage and gender groups of cysteine from food and supplements is 1.0 g/d (Appendix Table D-5)
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From page 712... ...
The glutamate that escapes capture by the gut is largely taken up by the liver. Glutamate is also synthesized endogenously as a product of transamination of other amino acids during the catabolism of arginine, proline, and histidine, and by the action of glutaminase on glutamine.
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From page 713... ...
. Moreover, no adverse effects on body weight gain, food consumption, behavior, electrocardiogram, ophthal
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From page 714... ...
Despite the generally low level of toxicity of glutamic acid demonstrated in the studies on animals and humans, there has remained concern over its continued use as a flavor-enhancing agent. This has been fueled by the discovery that high doses of glutamate can under certain circumstances be neurotoxic (Olney, 1969)
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From page 715... ...
might therefore be interpreted to imply that the elevated concentration of glutamate was penetrating the hypothalamus in humans, and that neuroendocrine disturbances might be a potential consequence. However, a more recent and more strictly controlled study, employing 12.7 g of monosodium glutamate (160 mg/kg of body weight)
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From page 716... ...
. Thus in 1988, JECFA concluded that properly conducted and controlled clinical trials had failed to establish a relationship between Chinese Restaurant Syndrome and the ingestion of MSG.
|
From page 717... ...
Because high concentrations of either glutamic acid or ammonia are known to be
|
From page 718... ...
Plasma glutamine was modestly increased and nitrogen balances were improved compared with the control group. In addition, no adverse effects were observed.
|
From page 719... ...
. DoseResponse Assessment The only reported adverse effect of glutamine was an increase in liver enzymes in patients on TPN supplemented with glutamine (0.285 g/kg body weight/d, corresponding to about 20 g/d)
|
From page 720... ...
, removal of histidine from the diet, unlike the eight classical indispensable amino acids, does not induce negative nitrogen balance in the first 10 days (Rose et al., 1951)
|
From page 721... ...
Hazard Identification Adverse Effects in Animals. Histidine given acutely by intraperitoneal injection or intravenously has been shown to result in changes in the concentration of brain amino acids (Oishi et al., 1989)
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From page 722... ...
. Male rats were fed diets containing 0.47 and 0.96 g/kg body weight/d of HMHC for 104 weeks; female rats were fed 0.56 and 1.1 g/kg body weight/d for the same period.
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From page 723... ...
. Based on distribution data from the 19881994 NHANES III, the mean daily intake for all life stage and gender groups of lysine from food and supplements is 5.3 g/d (Appendix Table D-11)
|
From page 724... ...
. Similarly, no adverse effects were reported when 1- to 5-month-old infants were given up to 220 mg/kg body weight of lysine for 15 days (Snyderman et al., 1959b)
|
From page 725... ...
. Humans, as well as other mammals, cannot fix inorganic sulfur into organic molecules and must rely on ingested sulfur amino acids, such as methionine, for the synthesis of protein and biologically active sulfur.
|
From page 726... ...
. High doses of methionine (~100 mg/kg of body weight)
|
From page 727... ...
. Unlike most other amino acids, excessive ingestion of L-phenylalanine can be complicated by the coexistence of genetic disorders.
|
From page 728... ...
Proline L-Proline is a dispensable amino acid that can be formed from and converted to glutamic acid. It is incorporated into tissue proteins and can then be hydroxylated to form hydroxproline.
|
From page 729... ...
Serine Serine is a dispensable amino acid that is synthesized endogenously from D-3 phosphoglycerate or glycine. Based on distribution data from the 19881994 NHANES III, the mean daily intake for all life stage and gender groups of serine from food and supplements is 3.5 g/d (Appendix
|
From page 730... ...
Similar to L-lysine, L-threonine does not take part in transamination reactions. Based on distribution data from the 19881994 NHANES III, the mean daily intake for all life stage and gender groups of threonine from food and supplements is 3.0 g/d (Appendix Table D-16)
|
From page 731... ...
DoseResponse Assessment The data on the adverse effects of L-threonine intake from supplements were not available for a doseresponse assessment and derivation of a UL in apparently healthy humans. Tryptophan L-Tryptophan, an indispensable amino acid, serves as a precursor for several small molecules of functional significance including the vitamin niacin, the neurotransmitter serotonin, the metabolite tryptamine, and the pineal hormone melatonin.
|
From page 732... ...
. Addition of 2.5 or 5 percent L-tryptophan to diets of rats and mice for 2 years resulted in decreased body weights of male and female mice and male (but not female)
|
From page 733... ...
reported sustained nystagmus and drowsiness in seven adults given 70 and 90 mg/kg of body weight of L-tryptophan orally in single doses, but found that these effects were absent at 30 or 50 mg/kg. However, Lieberman and coworkers (1985)
|
From page 734... ...
L-Tyrosine is a precursor of several biologically active substances, including catecholamine neurotransmitters, hormones, and melanin skin pigments. Based on distribution data from the 19881994 NHANES III, the mean daily intake for all life stage and gender groups of tyrosine from food and supplements is 2.8 g/d (Appendix Table D-18)
|
From page 735... ...
Single oral doses of 100 or 150 mg/kg of L-tyrosine administered to humans lead to a two- to threefold increase in plasma tyrosine concentrations (Cuche et al., 1985; Glaeser et al., 1979) and in urinary excretion of catecholamines and their metabolites (Alonso et al., 1982)
|
From page 736... ...
All amino acids had their highest median intake for any life stage and gender group in men aged 19 through 30 years. The highest intakes at the 99th percentile were also found in men, with those 51 TABLE 10-29 Highest Median and 99th Percentile of Usual Daily Intake of Amino Acids, United States, Third National Health and Nutrition Examination Survey, 19981994 Highest Median Highest 99th Percentile of Amino Acid Intakea (g/d)
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From page 737... ...
· The role of the gastrointestinal system in the metabolism of amino acids, the nature of the amino acid losses, and the extent of synthesis of indispensable amino acids need to be investigated. · Research on adaptation mechanisms at various intakes of protein is needed.
|
From page 738... ...
1990. Dietary branched-chain amino acids and protein selection by rats.
|
From page 739... ...
1984. Adverse effects of excessive consumption of amino acids.
|
From page 740... ...
In: Friedman M, ed. Absorption and Utilization of Amino Acids, Vol.
|
From page 741... ...
1989. Stimulation of pituitary hormone secretion by neurotransmitter amino acids in humans.
|
From page 742... ...
1993. Protein turnover in the human fetus studied at term using stable isotope tracer amino acids.
|
From page 743... ...
2000. Protein-bound D-amino acids, and to a lesser extent lysinoalanine, decrease true ileal protein digestibility in minipigs as determined with 15N-labeling.
|
From page 744... ...
1983. Effects of ingested steak and infused leucine on forelimb metabolism in man and the fate of the carbon skeletons and amino groups of branched-chain amino acids.
|
From page 745... ...
1973. Energy and Protein Requirements.
|
From page 746... ...
1990. Role of insulin and branched-chain amino acids in regulating protein metabolism during fast ing.
|
From page 747... ...
1978. Human protein requirements: Inter relationships between energy intake and nitrogen balance in young men consuming the 1973 FAO/WHO safe level of egg protein, with added non essential amino acids.
|
From page 748... ...
In: Blackburn GL, Grant JP, Young VR, eds. Amino Acids.
|
From page 749... ...
1963. Variation in requirements of nutrients: amino acids.
|
From page 750... ...
1981. A study of growth hormone release in man after oral administration of amino acids.
|
From page 751... ...
II. Effects on acidic and neutral amino acids.
|
From page 752... ...
1990. Transport of amino acids by the human placenta: Pre dicted effects thereon of maternal hyperphenylalaninaemia.
|
From page 753... ...
1987. Newer concepts of the indispensable amino acids.
|
From page 754... ...
1959. Relationship between plasma amino acids and composition of ingested protein.
|
From page 755... ...
1999. Proteins and amino acids.
|
From page 756... ...
1999b. Incorporation of urea and ammonia nitrogen into ileal and fecal microbial proteins and plasma free amino acids in normal men and ileostomates.
|
From page 757... ...
1964. Amino acid requirements of children: Nitrogen balance at the minimal level of essential amino acids.
|
From page 758... ...
1996. What are the essential amino acids for the preterm and term infant?
|
From page 759... ...
1987. Acute effects of dietary protein on food intake, tissue amino acids, and brain serotonin.
|
From page 760... ...
1990. Conversion of amino acids to specialized products.
|
From page 761... ...
1970. Response of adult rats to low dietary levels of essential amino acids.
|
From page 762... ...
1990. Branch-chain amino acids: Their metabolism and clinical utility.
|
From page 763... ...
Am J Clin Nutr 37:961968. Stegink LD, Filer LJ Jr, Baker GL.
|
From page 764... ...
1998. Catabolism dominates the first-pass intestinal metabolism of dietary essential amino acids in milk protein-fed piglets.
|
From page 765... ...
1961. Interactions of amino acids in renal tubular transport.
|
From page 766... ...
1971. Effect of excessive levels of lysine and threonine on the metabolism of these amino acids in rats.
|
From page 767... ...
1975a. Protein requirements of man: Comparative nitrogen balance response within the submaintenance-to-maintenance range of intakes of wheat and beef proteins.
|
From page 768... ...
1976b. Nitrogen retention in men fed varying levels of amino acids from soy protein with or without added L-methionine.
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Key Terms
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