Dietary Reference Intakes The Essential Guide to Nutrient Requirements (2006) / Chapter Skim
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From page 144... ...
TABLE 1 Dietary Reference Intakes for Total Protein by Life Stage Groupa DRI values (g/kg/day) EARb RDAc AId males females males females Life stage group 0 through 6 mo 1.52 (9.1)
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PART II: PROTEIN AND AMINO ACIDS 145 PROTEIN AMINO ACIDS AND P roteins form the major structural components of all the cells of the body. Proteins also function as enzymes, in membranes, as transport carriers, and as hormones.
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From page 146... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 146 PROTEIN AND THE BODY Function Protein is the major functional and structural component of every cell in the body. All enzymes, membrane carriers, blood transport molecules, the intracel lular matrices, hair, fingernails, serum albumin, keratin, and collagen are pro teins, as are many hormones and a large part of membranes.
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From page 147... ...
PART II: PROTEIN AND AMINO ACIDS 147 TABLE 2 Indispensable, Dispensable, and Conditionally Indispensable Amino Acids in the Human Diet Precursors of Conditionally Conditionally Indispensablea Indispensable Dispensable Indispensable Histidineb Alanine Arginine Glutamine/glutamate, aspartate Isoleucine Aspartic acid Cysteine Methionine, serine Leucine Asparagine Glutamine Glutamic acid/ammonia Lysine Glutamic acid Glycine Serine, choline Methionine Serine Proline Glutamate Phenylalanine Tyrosine Phenylalanine Threonine Tryptophan Valine a Conditionally indispensable is defined as requiring a dietary source when endogenous synthesis cannot meet metabolic need. b Although histidine is considered indispensable, unlike the other eight indispensable amino acids, it does not fulfill the criteria of reducing protein deposition and inducing negative nitrogen balance promptly upon removal from the diet.
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From page 148... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 148 When proteins are ingested from food, they are denatured by stomach acid. In the stomach, they are also cleaved into smaller peptides by the enzyme pep sin, which is activated in response to a meal.
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From page 149... ...
PART II: PROTEIN AND AMINO ACIDS 149 body tissues are more active than others with regard to it. Despite their rather small contribution to the total protein content of the body, the liver and the intestine together are believed to contribute as much as 50 percent of whole body protein turnover.
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From page 150... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 150 needs, and some evidence supports this assumption. Thus, it is prudent that women carrying twins should increase their protein intake by an additional 50 g/day beginning in the second trimester, as well as ensure for themselves a sufficient energy intake to utilize the protein as efficiently as possible.
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From page 151... ...
PART II: PROTEIN AND AMINO ACIDS 151 The UL The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse effects for almost all people.
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From page 152... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 152 ized world, PEM is predominately seen in hospitals, is associated with disease, or is often found in the elderly. Protein deficiency has been shown to affect all of the body's organs and many of its systems, including the brain and brain function of infants and young children; the immune system, thus elevating risk of infection; gut mucosal func tion and permeability, which affects absorption and vulnerability to systemic disease; and kidney function.
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From page 153... ...
PART II: PROTEIN AND AMINO ACIDS 153 Phenylketonuria (PKU) : PKU is a genetic disorder that impairs activity of the enzyme phenylalanine hydroxylase (PAH)
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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 154 KEY POINTS FOR PROTEIN AND AMINO ACIDS Protein is the major functional and structural component of 3 every cell in the body. All enzymes, membrane carriers, blood transport molecules, the intracellular matrices, hair, fingernails, serum albumin, keratin, and collagen are proteins, as are many hormones and a large part of membranes.
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From page 155... ...
PART II: PROTEIN AND AMINO ACIDS 155 Protein deficiency has been shown to affect all of the body's 3 organs and many systems. The data are conflicting on the potential for high-protein diets 3 to produce gastrointestinal effects, changes in nitrogen balance, or chronic disease, such as osteoporosis or renal stones.
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