Primary Fuel Source for Enterocytes
The primary fuel source for enterocytes (intestinal epithelial cells) is glutamine (option e).
Evidence Supporting Glutamine as Primary Fuel
Glutamine serves as the principal energy source for enterocytes, as clearly identified in multiple high-quality guidelines and research:
- The ESPEN guidelines specifically identify glutamine as "a primary fuel source for epithelial enterocytes" 1
- Glutamine is the most abundant amino acid in plasma and cells, and is the preferred fuel for enterocytes in the small intestine 2
- It provides not only energy but also supports intestinal barrier structure and function 1
Comparison with Other Potential Fuel Sources
Short-chain fatty acids (option a)
- While short-chain fatty acids are important metabolites in the intestine, they are not the primary energy source for enterocytes
- Short-chain fatty acids are primarily produced by bacterial fermentation in the colon and serve as energy sources for colonocytes rather than small intestinal enterocytes
Glucose (option b)
- The ESPEN guidelines note that glucose is the main metabolic fuel for the brain, peripheral nerves, renal medulla, leukocytes, erythrocytes and bone marrow 3
- However, glucose is not identified as the primary energy source for enterocytes
Triglycerides (option c) and Lactulose (option d)
- No evidence supports these as primary fuel sources for enterocytes
- Triglycerides require processing before utilization
- Lactulose is a non-absorbable disaccharide used primarily as a laxative
Metabolic Mechanisms of Glutamine in Enterocytes
Glutamine metabolism in enterocytes involves several key processes:
- It serves as the principal energy source through its conversion to glutamate and subsequently to α-ketoglutarate, which enters the TCA cycle 4
- Glutamine deprivation from the apical (luminal) side significantly reduces enterocyte function, including expression of disaccharidases and Na+/K+-ATPase 4
- Bidirectional supply of glutamine (both luminal and serosal) maintains optimal ATP levels in enterocytes 5
Clinical Implications
The role of glutamine as the primary fuel source for enterocytes has important clinical implications:
- Glutamine supplementation can restore enterocyte function and maintain intestinal barrier integrity 4
- During critical illness or after severe burns, glutamine requirements increase significantly 2
- Glutamine deprivation can lead to diminished intestinal function, mucosal atrophy, and increased bacterial translocation 4
Conclusion
Based on the most recent and highest quality evidence, glutamine is definitively the primary fuel source for enterocytes, making option (e) the correct answer.