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.[citation needed] 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.