Which amino acid is the key fuel for the small intestine?

• A. Alanine
• B. Leucine
• C. Glutamine
• D. Arginine

Answer: (C)

Glutamine is the preferred energy source for enterocytes, the cells lining the small intestine. These cells have high energy demands and use glutamine efficiently, oxidizing it in mitochondria to generate ATP while also providing nitrogen for nucleotide synthesis to support rapid mucosal turnover. This dual role helps maintain gut barrier integrity and function, especially during stress or illness when the gut needs extra support.

Alanine is more associated with nitrogen transport and hepatic gluconeogenesis rather than fueling the gut. Leucine is primarily used by muscle for protein synthesis and energy through branched-chain amino acid oxidation, not by enterocytes. Arginine supports mucosal blood flow and nitric oxide production, contributing to gut health, but it is not the main energy substrate for the intestinal lining.