Recommended Dietary Allowances 10th Edition (1989) / Chapter Skim
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Protein and Amino Acids
Protein and Amino Acids
Pages 52-77
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From page 52... ...
A continuous supply of dietary amino acids is required to replace these losses, even after growth has ceased. In this chapter, protein is equated with nitrogen x 6.25, i.e., crude protein containing 1670 nitrogen.
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From page 53... ...
These are commonly called the essential amino acids. Histidine is an essential amino acid for infants, but was not demonstrated to be required by adults until recently (Cho et al., 1984; Kopple and Swendseid, 1981~.
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From page 54... ...
of nitrogen per kilogram daily (WHO, 19851.5 In the past, a factorial method was used as a basis for predicting the protein requirements of various age groups. For adults, the requirement for dietary protein was considered to be the amount needed to replace the obligatory nitrogen loss after adjustment for inefficiency in utilization of dietary protein and for the quality of the dietary protein consumed (i.e., its digestibility and amino acid composition)
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From page 55... ...
To estimate the protein requirement, levels of dietary protein below and near predicted adequate intake are fed and nitrogen balance is measured at each level. The requirement is estimated by interpolating or extrapolating the nitrogen balance data to the zero balance point (nitrogen equilibrium)
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From page 56... ...
The required amounts of the nine essential amino acids must be provided in the diet, but because cystine can replace approximately 30% of the requirement for methionine, and tyrosine about 50% of the requirement for phenylalanine, these amino acids must also be considered. The essential amino acid requirements of infants, children, men, and women were studied extensively from 1950 to 1970.
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From page 57... ...
Studies of whole body lysine, leucine, valine, and threonine oxidation rates suggest that adult requirements for these essential amino acids have been underestimated. Approximations of average requirements according to the '~C tracer studies are leucine, 40 mg/kg (Meguid et al., 1986a)
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From page 58... ...
food consumption patterns to determine if adjustment of the allowance for reference protein would be warranted in establishing the RDA for protein due to amino acid composition or protein digestibility of food proteins consumed. The Requirement for Reference Protein and Its Variability Adults To determine the protein requirements of young male adults, WHO (1985)
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From page 59... ...
Dietary protein needs might be expected to change during the aging process, i.e., to decrease due to lower rates of turnover, or to increase due to decreased efficiency of absorptive and metabolic processes and to decreased total food intake associated with reduced physical activity, or to become more variable due to disease and disability. There is surpr~s~ng~y little Norma on on which to base recommendations for protein intake in the elderly.
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From page 60... ...
Consequently, increased protein needs during pregnancy may be more uniform across time than the figures of Hytten and Leitch indicate. Nitrogen balance data can also be used to estimate protein requirements during pregnancy.
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From page 61... ...
Despite these discrepancies between factorial and nitrogen balance estimates of nitrogen gain during pregnancy, the subcommittee concurs with WHO (1985) that the estimate of requirement should be based on the factorial method.
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From page 62... ...
Analyses of human milk composition in the United States, based on a study of 40 mothers in the first 4 months of lactation, show a fall in protein content from 1.36 g/100 ml to 1.12 g/100 ml during this period (Butte et al., 1984~. The average protein requirement for lactation is estimated from milk composition and the mean volume of milk produced, which is 750 mI/day, adjusted for 70% efficiency in the conversion of dietary protein to milk protein.
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From page 63... ...
The figures given for protein are nitrogen x 6.25. Approximately 20% of the nitrogen in human milk is nonprotein nitrogen (e.g., amino acids, urea' nucleotides)
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From page 64... ...
. Amino Acid Requirement Pattern According to Age A pattern of requirements for amino acids in the total dietary protein is calculated by dividing each essential amino acid requirement by the recommended allowance of reference protein for the given age group (see Table 6-5~.
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From page 66... ...
Dietary Protein Derived Allowance Of Recommended Dietary Reference Proteina Allowance (g/kg)
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From page 68... ...
The amino acid score should be based on the appropriate pattern for age. Only four essential amino acids are likely to affect the protein quality of mixed human diets: lysine, the sulfur-containing amino acids (methionine plus cystine)
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From page 69... ...
There are few data on the digestibility of specific amino acids in food proteins, and any differences are not captured in measurements of overall protein digestibility. Although it is known that there are differences between the pattern of amino acids in food protein, fecal matter, and portal blood, it is not now possible to provide finer adjustment than overall digestibility.
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From page 70... ...
sources consumed and an amino acid score based on their contribution of essential amino acids. Such adjustment would rarely be warrantee!
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From page 71... ...
Vigorous activity that leacls to profuse sweating, such as in heavy work and sports, and exposure to heat increases nitrogen loss from the skin, but with acclimatization to a warm environment, the excessive skin loss is reduced and may be partially compensated by decreased renal excretion (WHO, 1985~. In view of the margin of safety in the RDA, no increment is adcled for work or training.
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From page 72... ...
Human milk or an equivalent substitute (i.e., formula containing as much protein and a similar amino acid pattern, corrected for digestibility if warranted) is recommended for infants from birth to 3 months of age.
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From page 73... ...
1982. Dietary protein intake and the progressive nature of kidney disease: the role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation, and intrinsic renal disease.
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From page 74... ...
1977. Human protein requirements: a long-term metabolic nitrogen balance study in young men to evaluate the 1973 FAD/WHO safe level of egg protein intake.
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From page 75... ...
1964. Amino acid requirements of children: nitrogen balance at the minimum level of essential amino acids.
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From page 76... ...
1964. Nitrogen balances of men over 65 fed the FAO and milk patterns of essential amino acids.
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From page 77... ...
1979. Protein requirements of elderly men.
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