What is a role of the gut microbiota in the large intestine?

• A. Fermentation of undigested carbohydrates producing short-chain fatty acids
• B. Secretion of intrinsic factor
• C. Absorption of vitamin B12
• D. Digestion of proteins in stomach

Answer: (A)

The gut microbiota in the large intestine mainly ferments undigested carbohydrates, producing short-chain fatty acids such as acetate, propionate, and butyrate. These fatty acids provide energy to colonocytes, especially butyrate, help maintain the gut mucosal barrier, and influence water absorption, inflammation, and metabolic regulation.

Other processes described occur outside this microbial role: the secretion of intrinsic factor happens in the stomach by parietal cells, and vitamin B12 absorption occurs later in the ileum with intrinsic factor. Digestion of proteins in the stomach is achieved by gastric enzymes like pepsin, not by the large-intestine microbiota.