What percent of amino acids released from degraded protein are re-utilized for protein synthesis in adults?

• A. 60-70%
• B. 40-50%
• C. 70-80%
• D. 90-95%

Answer: (D)

Amino acid recycling during adult protein turnover is highly efficient. In adults, proteins continually break down and are rebuilt, so the amino acids released from degradation are largely reused to make new proteins rather than wasted. The body keeps a pool of amino acids on hand for ongoing tissue maintenance, and most of the liberated amino acids are redirected back into protein synthesis. Only a small portion—about 5–10%—is diverted to energy production, gluconeogenesis, or loss as urea; the rest go back into making body proteins. This is why the estimate for re-utilization falls around 90–95%.