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  • EAR and RDA for Amino Acids

    Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for amino acids (protein) for healthy adults 19 y and older, mg/kg/day:

    • Estimated Average Requirement (EAR): average, estimated to meet the requirements of 50%.
    • Recommended Dietary Allowance (RDA): average, sufficient to meet the nutrient requirements of nearly all.
    Amino Acids EAR RDA
    phenylalanine + tyrosine 27 33
    valine 19 24
    threonine 16 20
    tryptophan 4 5
    methionine + cysteine 15 19
    leucine 34 42
    isoleucine 15 19
    lysine 31 38
    histidine 11 14

  • Amino Acid Requirements for Adults

    Estimates of Amino Acid Requirements for adults, mg / kg per day

    • Phenylalanine + tyrosine: 14
    • Leucine: 14
    • Methionine + cystine: 13
    • Histidine: 8–12
    • Lysine: 12
    • Isoleucine: 10
    • Valine: 10
    • Threonine: 7
    • Tryptophan: 3.5

  • All Essential Amino Acids

    An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized by the organism, and must be supplied in diet. 

    The 9 amino acids humans cannot synthesize (F V T W M L I K H):

    • phenylalanine
    • valine
    • threonine
    • tryptophan
    • methionine
    • leucine
    • isoleucine
    • lysine
    • histidine

    Animal and plant proteins are made up of about 20 common amino acids.

    Synthesis of 6 other amino acids - conditionally essential - can be limited under special conditions (R C G Q P Y): arginine, cysteine, glycine, glutamine, proline, and tyrosine.

    Dispensable amino acids can be synthesized in the human body, 5 (A D N E S): alanine, aspartic acid, asparagine, glutamic acid and serine .

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Linus Pauling

I have something that I call my Golden Rule. It goes something like this: 'Do unto others twenty-five percent better than you expect them to do unto you.' … The twenty-five percent is for error.

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Protein Digestibility-Corrected Amino Acid Score

The protein digestibility-corrected amino acid score (PDCAAS) has been adopted by FAO/WHO as the preferred method for the measurement of the protein value in human nutrition. 

PDCAAS = Amino Acid Score x Digestibility

The method is based on comparison of the concentration of the first limiting essential amino acid in the test protein with the concentration of that amino acid in a reference (scoring) pattern. This scoring pattern is derived from the essential amino acid requirements of the preschool-age child.

Although the principle of the PDCAAS method has been widely accepted, critical questions have been raised in the scientific community:

  1. the validity of the preschool-age child amino acid requirement values (more than 4 times greater than the EAA requirement for an adult),
  2. the validity of correction for fecal instead of ileal digestibility,
  3. the truncation of PDCAAS values to 100%.

The reference scoring pattern was based on studies performed more than 25 years ago on a limited number of 2-year-old children recovering from malnutrition.

According to the current official recommendations, a 2-year old child needs ~ 3x higher essential-to-non-essential amino acid ratio, and needs essential amino acids in different proportions than adult. Methionine/cysteine is the limiting essential amino acids for adults, and for children it is lysine or tryptophan.

The use of fecal digestibility overestimates the nutritional value of a protein because amino acid nitrogen entering the colon is lost for protein synthesis in the body and is, at least in part, excreted in urine as ammonia.

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