Short chain fatty acids are produced by fermentation of which substrate?

• A. Proteins
• B. Fats
• C. Amino acids
• D. Complex carbohydrates

Answer: (D)

Short-chain fatty acids come from the fermentation of non-digestible carbohydrates by gut bacteria. When dietary fiber and other resistant carbohydrates reach the colon, the microbiota break them down and produce acetate, propionate, and butyrate, which are the main SCFAs and provide energy to colonocytes and help regulate inflammation and gut health. Proteins and amino acids undergo proteolytic fermentation, yielding different metabolites such as branched-chain fatty acids and ammonia rather than the typical SCFAs. Fats are not fermented in this way. So the substrate for SCFA production is complex carbohydrates.