Short-chain fatty acid explained

Short-chain fatty acids (SCFAs) are fatty acids of two to six carbon atoms.^[1] The SCFAs' lower limit is interpreted differently, either with one, two, three or four 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.

List of SCFAs

Lipid number	Name		Salt/Ester Name		Formula		Mass (g/mol)	Diagram
	Common	Systematic	Common	Systematic	Molecular	Structural
C2:0	Acetic acid	Ethanoic acid	Acetate	Ethanoate			60.05
C3:0	Propionic acid	Propanoic acid	Propionate	Propanoate			74.08
C4:0	Butyric acid	Butanoic acid	Butyrate	Butanoate			88.11
C4:0	Isobutyric acid	2-Methylpropanoic acid	Isobutyrate	2-Methylpropanoate			88.11
C5:0	Valeric acid	Pentanoic acid	Valerate	Pentanoate			102.13
C5:0	Isovaleric acid	3-Methylbutanoic acid	Isovalerate	3-Methylbutanoate			102.13
C5:0	2-Methylbutyric acid	2-Methylbutyric acid	2-Methylbutanoate	2-Methylbutanoate			102.13

Functions

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. 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.^[5]

SCFAs and medium-chain fatty acids are primarily absorbed through the portal vein during lipid digestion,^[6] 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, affecting the production of lipids, energy, and vitamins.^{[1] [2] [7]} They may affect appetite and cardiometabolic health.

See also

• 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

Further reading

• A review of the biological properties of SCFA from the Danone Institute via archive.org

Notes and References

1. Book: Brody T . Nutritional Biochemistry. 1999. Academic Press. 978-0121348366. 2nd. December 21, 2012. 320.
2. Canfora EE, Jocken JW, Blaak EE . Short-chain fatty acids in control of body weight and insulin sensitivity . Nature Reviews. Endocrinology . 11 . 10 . 577–591 . October 2015 . 26260141 . 10.1038/nrendo.2015.128 . 1263823 .
3. Wong JM, de Souza R, Kendall CW, Emam A, Jenkins DJ . Colonic health: fermentation and short chain fatty acids . Journal of Clinical Gastroenterology . 40 . 3 . 235–243 . March 2006 . 16633129 . 10.1097/00004836-200603000-00015 . 46228892 .
4. Mueller NT, Zhang M, Juraschek SP, Miller ER, Appel LJ . Effects of high-fiber diets enriched with carbohydrate, protein, or unsaturated fat on circulating short chain fatty acids: results from the OmniHeart randomized trial . The American Journal of Clinical Nutrition . 111 . 3 . 545–554 . March 2020 . 31927581 . 7049528 . 10.1093/ajcn/nqz322 .
5. Roy CC, Kien CL, Bouthillier L, Levy E . Short-chain fatty acids: ready for prime time? . Nutrition in Clinical Practice . 21 . 4 . 351–366 . August 2006 . 16870803 . 10.1177/0115426506021004351 .
6. Book: Kuksis A . Fat Digestion and Absorption. 2000. The American Oil Chemists Society. 978-1893997127. https://books.google.com/books?id=t5FNYzGEUDsC&pg=PA163. Christophe AB, DeVriese S . December 21, 2012. 163. Biochemistry of Glycerolipids and Formation of Chylomicrons.
7. Byrne CS, Chambers ES, Morrison DJ, Frost G . The role of short chain fatty acids in appetite regulation and energy homeostasis . International Journal of Obesity . 39 . 9 . 1331–1338 . September 2015 . 25971927 . 4564526 . 10.1038/ijo.2015.84 .