Essential amino acids (EAAs)

Essential amino acids (EAAs) are the nine amino acids the body can’t make and must get from food.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 197.} The body’s proteins use 20 amino acids in total; some are conditionally essential, normally made in the body but needed from food during illness and stress.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 197.} The nine EAAs are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 222.}

A shortage of even one EAA impairs the synthesis of almost every protein in the cell.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 222.} After training, net protein balance stays negative until the client eats; providing EAAs turns it positive quickly.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 222.}

In practice

• Protein quality depends largely on EAA content and digestibility; eggs, dairy, meat, fish and poultry contain all nine.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 197.}
• Most plant foods fall short in one or more EAAs, but vegetarian and vegan clients can cover them by eating a variety of legumes, vegetables, seeds, nuts, rice and whole grains over the day.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 198.}
• In younger adults, 20 to 25 g of high-quality protein after training supplies about 8.5 to 10 g of EAAs and maximally stimulates muscle protein synthesis.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 228.} Older adults may need 40 g or more of protein.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 228.}
• Schoenfeld puts saturation of the muscle protein synthesis response at about 10 g of EAAs; beyond that, extra amino acids go to other processes or are burned.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 231.}