What is the principal metabolic fuel for intestinal cells?

• A. Glutamine
• B. Glucose
• C. Fatty acids
• D. Lactate

Answer: (A)

Glutamine serves as the primary energy and nitrogen source for enterocytes, the cells lining the small intestine. These rapidly dividing cells rely on glutaminolysis to fuel the TCA cycle, converting glutamine to glutamate and then to alpha-ketoglutarate to generate ATP and support biosynthesis. This substrate supports not only energy needs but also nucleotide synthesis and maintenance of the mucosal barrier, which is crucial for gut integrity and repair. While glucose can be used by enterocytes and fatty acids are utilized by many cells, glutamine is the preferred fuel for intestinal cells, especially during growth, turnover, or stressed states. Lactate can be utilized by some tissues as fuel, but it is not the main substrate for enterocytes.