Short-chain fatty acid formation at fermentation of indigestible carbohydrates

Short chain fatty acids (SCFAs; acetic, propionic and butyric acid) are formed during bacterial fermentation of carbohydrates in the colon. The interest in SCFA production is related to an increasing body of knowledge of the physiological effects of these acids. SCFAs are important anions in the colonic lumen and serve locally as nutrients for the mucosa cells, stimulating mucosal proliferation and blood flow. Especially butyric acid has been emphazised. It is the main energy substrate for the colonocytes and has been suggested to play a role in the prevention and treatment of diseases of the colonic mucosa, such as distal ulcerative colitis and cancer. SCFA production decreases the luminal pH, and may thereby stimulate mineral absorption and reduce secondary bile acid formation in the colon. Colonic generation of SCFAs has also been related to systematic and metabolic effects, e.g. SCFAs may influence the motility along the gastrointestinal tract and propionic acid has been suggested to inhibit the cholesterol synthesis from acetic acid in the liver. The SCFA formed at fermentation is quantitatively and qualitatively influenced by the type and amount of carbohydrate substrate. Further, certain combinations of carbohydrates may have synergistic effects on the SCFA pattern and may also shift the site of fermentation. This opens possibilities to design foods with tailored features regarding SCFA release in the human colon with potential health implications. There is a potential that in the future it will be possible to control SCFA production in the colon regarding pattern and place for release.