35 AAs - Protein Requirements and Quality

35 AAs - Protein Requirements and Quality - Amino Acids and...

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Amino Acids and Proteins: Protein Requirements and Protein Quality HNFE 3025 Fall 2009
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Protein is needed for growth and maintenance of all living cells. Constant need for amino acids for protein synthesis For protein synthesis, all 20 of the common AAs are essential and must be present in sufficient quantities Dispensable and indispensible AAs Sources are dietary and degradation of existing proteins Because of the lack of storage of proteins or amino acids and the obligatory losses of protein, a certain amount of protein is essential in the diet. Protein and AA Essentiality 2
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Influenced by a number of factors Age Growing years, increasing protein mass Body size Needs increase with increased body mass Physiological state Health, activity level, pregnancy and lactation Energy intake Needs increase with lowered food energy intake because efficiency of AA utilization depends on energy balance Dietary Protein Requirements 3
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Expressed as recommended dietary allowances (RDA). The most recent from 2002. Typically expressed as g/kg body weight/d Recommended protein intakes for USA equal or lower than those from other nations. Median intake for adult US men & women ~25% > RDA. It is more than this for those physically active Protein Requirements 4 Life stage Current RDA (g/kg/d) 0-6 months 1.52 expressed as AI (adequate intake) 7-12 months 1.5 1-3 years 1.1 4-13 years 0.95 14-18 years 0.85 19+ years 0.8 pregnancy 1.1 lactation 1.1
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There is no change in AA content of the body Dietary intake of every AA is exactly balanced by losses In digestion Metabolism Secretions, skin, hair, nails, etc. Considered to occur at N equilibrium Because dietary PRO intake varies widely, mechanisms balance disposal with intake Major control point is rate of AA oxidation Maintenance 5
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Protein Requirements 6 % of Daily Protei n Needs Age 0-3 mo 3-7 mo 1-3 yr 4-13 yr18 yr Growth Maintenance
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Growth vs. Maintenance Stages of life Growth implies new tissue mass Maintenance – even when no protein is consumed, N is lost through protein turnover Obligatory losses – dietary protein must be consumed to replace these losses Life Stage PRO syn (g/kg/d) Newborn 17.4 Infant 6.9 Adult 3.0 Elderly 1.9 7
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AA oxidation during endurance exercise is 1-6% of total energy expended Lower with sufficient CHO and energy Drops with training adaptation Higher on high protein diet – WHY?
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35 AAs - Protein Requirements and Quality - Amino Acids and...

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