Which amino acid is described as the principal metabolic fuel for intestinal cells?

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

Answer: (A)

Glutamine is the main energy source for intestinal cells. Enterocytes take up glutamine at high rates and metabolize it through glutaminolysis, converting it to glutamate and then to α-ketoglutarate to fuel the TCA cycle. This provides the ATP needed for the rapid turnover and barrier maintenance of the intestinal mucosa, making glutamine especially important in situations of gut stress or injury. Arginine, while important for nitric oxide production and immune function, is not the primary fuel for gut cells. Leucine mainly drives protein synthesis and signaling via mTOR, and lysine is essential for growth and protein synthesis but does not serve as the gut’s principal energy substrate.