Glossary
Short-chain fatty acids.
Direct answer
Short-chain fatty acids are produced when gut bacteria ferment plant fibre that the body's own enzymes cannot split. The main ones are acetate, propionate and butyrate. Short-chain fatty acids are taken up across the gut wall, fuel the cells lining the intestine and contribute to the energy supply of the whole organism.
Short-chain fatty acids are not dietary fat. They do not come from the fat fraction of the ration but from the fermentation of carbohydrates that reach the large intestine undigested. Equating them with cooking oils obscures both their origin and the role of the gut microbiota, without which these acids would not exist.
The difference between species is striking here. In the horse, a hindgut fermenter, short-chain fatty acids from caecal fermentation cover a major part of daily energy needs. In humans, colonic fermentation adds only a supplement, because most energy has already been absorbed in the small intestine as starch, fat and protein.
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