Which amino acid is considered conditionally essential and serves as a major energy source for intestinal cells?

• A. Tryptophan
• B. Glutamine
• C. Proline
• D. Arginine

Answer: (B)

Glutamine becomes conditionally essential in stress and is the primary fuel used by intestinal cells. The enterocytes lining the gut have a high energy demand to maintain their rapid turnover and barrier function, and they rely heavily on glutamine for energy, as well as for nucleotide synthesis and supporting immune activity within the gut. Under normal conditions the body can synthesize enough nonessential amino acids, but during illness or trauma the increased demand for glutamine outpaces supply, making supplementation important for gut integrity and function.

Tryptophan is mainly a precursor for serotonin and niacin, not a major energy source for the gut. Proline is important for collagen synthesis and has some metabolic roles, but it does not serve as the gut’s primary energy substrate. Arginine supports nitric oxide production and immune function and has other metabolic roles, but again it is not the main energy source for intestinal cells.