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.

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

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 .