Short-chain fatty acids (SCFAs) are fatty acids of two to six carbon atoms.^[1] The SCFAs lower limit is interpreted differently, either with 1, 2, 3 or 4 carbon atoms. Derived from intestinal microbial fermentation of indigestible foods, SCFAs in human gut are acetic, propionic and butyric acid. They are the main energy source of colonocytes, making them crucial to gastrointestinal health.^[1][2] SCFAs all possess varying degrees of water solubility, which distinguishes them from longer chain fatty acids that are immiscible.

SCFAs are produced when dietary fiber is fermented in the colon.^[1][3] Macronutrient composition (carbohydrate, protein or fat) of diets affects circulating SCFAs.^[4]

Acetate, propionate and butyrate are the three most common SCFAs.^[3]

SCFAs and medium-chain fatty acids are primarily absorbed through the portal vein during lipid digestion,^[5] while long-chain fatty acids are packed into chylomicrons, enter lymphatic capillaries, then transfer to the blood at the subclavian vein.^[1]

SCFAs have diverse physiological roles in body functions.^[1][2] They can affect the production of lipids, energy and vitamins.^[6] They can also affect appetite and cardiometabolic health.^[4] Additionally they may have an impact on mental health and mood.^[7] The three main SCFAs, acetate, propionate and butyrate, were shown to lower blood pressure in experimental models,^{[8][9][10][11]} and clinical trials to determine their effect on hypertensive patients are underway.^[12] Butyrate is particularly important for colon health because it is the primary energy source for colonocytes (the epithelial cells of the colon).^[1][2] The liver can use acetate for energy.^[13]

• List of carboxylic acids
• Medium-chain fatty acid (MCFA), fatty acid with aliphatic tails of 6 to 12 carbons, which can form medium-chain triglycerides
• Long-chain fatty acid (LCFA), fatty acid with aliphatic tails of 13 to 21 carbons
• Very long chain fatty acid (VLCFA), fatty acid with aliphatic tails of 22 or more carbons