Glutamine is the Most Abundant Amino Acid in the Human Body
The most abundant amino acid in the human body is glutamine (answer choice d). 1
Evidence Supporting Glutamine as the Most Abundant Amino Acid
Glutamine is consistently identified as the most abundant free amino acid in the human body across multiple authoritative guidelines:
- According to ESPEN guidelines on parenteral nutrition for intensive care, glutamine "is the most abundant free amino acid" in the body 1
- Similarly, ESPEN guidelines on parenteral nutrition for pancreas confirm that "glutamine is the most abundant free amino acid in the body" 1
Physiological Significance of Glutamine
Glutamine plays numerous critical roles in human physiology:
- Functions as a carrier for nitrogen and carbon between organs 1
- Serves as a precursor for nucleotides and cellular protection through glutathione 1
- Acts as a regulator of ammonia and acid-base balance 1
- Participates in protein and glucose metabolism 1
- Provides a major fuel source for rapidly dividing cells, including immune cells 2
- Supports intestinal integrity and optimal immune function 3
Glutamine Production and Metabolism
- Under normal conditions, glutamine is not an essential amino acid as it has an endogenous production rate (predominantly in skeletal muscle) of approximately 50-80g/24h for an adult 1
- During critical illness, increased demand for glutamine utilization (for immune activity and repair) may not be adequately met, causing plasma levels to fall 1
Clinical Relevance of Glutamine Status
- Low plasma glutamine levels are associated with worse outcomes in critically ill patients 1
- In certain clinical conditions (burns, trauma), supplemental glutamine may be beneficial 1
- However, indiscriminate supplementation is no longer recommended for all critically ill patients 1
Comparison to Other Amino Acids
While the other answer choices (alanine, valine, leucine, and arginine) are important amino acids with various physiological roles, none of them are as abundant in the human body as glutamine:
- Alanine is involved in the glucose-alanine cycle but is not as abundant as glutamine
- Leucine and valine are essential branched-chain amino acids important for protein synthesis
- Arginine has roles in the urea cycle and as a precursor for nitric oxide but is not present in the same quantities as glutamine
Conclusion
Based on the most authoritative clinical guidelines, glutamine is definitively the most abundant amino acid in the human body, making answer choice (d) correct.