Which B vitamin is produced in the gut by bacteria and is essential for energy metabolism?

• A. Riboflavin
• B. Biotin
• C. Niacin
• D. Pantothenic acid

Answer: (B)

Biotin, a B vitamin produced by gut bacteria, is essential for energy metabolism because it acts as a coenzyme for several carboxylase enzymes. These enzymes drive key carboxylation reactions that connect carbohydrate, fat, and protein metabolism. For example, pyruvate carboxylase converts pyruvate to oxaloacetate, supporting gluconeogenesis and helping replenish the citric acid cycle; acetyl-CoA carboxylase is involved in fatty acid synthesis; propionyl-CoA carboxylase processes certain amino acids and odd-chain fatty acids. While a balanced diet supplies most vitamins, the gut microbiota can contribute a notable amount of biotin, which is why this vitamin is often highlighted in questions about gut-produced B vitamins. The other listed vitamins are important for energy metabolism too, but biotin’s distinction here is its production by gut bacteria and its role in these carboxylation steps.