Which of the following is NOT among the six conditionally indispensable amino acids?

• A. Arginine
• B. Lysine
• C. Cysteine
• D. Glutamine

Answer: (B)

Conditionally indispensable amino acids are those normally synthesized by the body but that must be provided by the diet under certain conditions, such as illness, trauma, rapid growth, or severe malnutrition. Lysine, in contrast, is an essential amino acid, meaning the body cannot make it at all and it must come from food in all typical conditions. The other amino acids listed are commonly cited as conditional: arginine may become essential during growth and metabolic stress; cysteine becomes essential when methionine availability is limited; and glutamine often becomes indispensable during severe illness or critical illness due to increased demand. Because lysine does not fall into the conditional category, it is the one that is not among the six conditional indispensable amino acids.