What energy-containing product is formed by anaerobic fermentation in the colon?

• A. Short-chain fatty acids
• B. Long-chain fatty acids
• C. Cholesterol
• D. Urea

Answer: (A)

Anaerobic fermentation in the colon by gut bacteria converts undigested carbohydrates into short-chain fatty acids, such as acetate, propionate, and butyrate. These fatty acids provide energy, with butyrate serving as the main fuel for colonocytes and acetate/propionate contributing to energy metabolism elsewhere in the body. The other options don’t fit because long-chain fatty acids are absorbed dietary fats processed earlier in the gut, cholesterol is primarily produced by the liver and not a direct product of colonic fermentation, and urea is a waste product from protein metabolism excreted by the kidneys.