Propionate

Propionate is the negatively charged conjugate base of propionic acid, a three-carbon short-chain fatty acid. In the human large intestine, it is one of the major short-chain fatty acids produced by the gut microbiota, together with acetate and butyrate. Colonic microorganisms generate propionate mainly by fermenting carbohydrates that escape digestion and absorption in the small intestine .^1,2

Different gut microorganisms can produce propionate through several metabolic pathways, so its production depends on both the substrates available for fermentation and the composition and metabolic activity of the microbial community. Fermentable dietary fibers and other nondigestible carbohydrates are important substrates for this microbial metabolism .²

After being produced in the colon, propionate is absorbed through the intestinal wall and enters the portal circulation. A substantial proportion is taken up by the liver, where its carbon can enter metabolic pathways including gluconeogenesis. Some propionate also reaches the systemic circulation. In addition to serving as a metabolic substrate, propionate can act as a signaling molecule through receptors that respond to short-chain fatty acids .^2,3

Propionate is a specific member of the short-chain fatty acid group and is not a synonym for SCFAs in general. It differs from propionic acid only in protonation state: propionic acid is the electrically neutral acid form, whereas propionate is its negatively charged conjugate base .¹