SHORT-CHAIN FATTY-ACIDS IN THE HUMAN COLON - RELATION TO GASTROINTESTINAL HEALTH AND DISEASE

Fermentation, the process whereby anaerobic bacteria break down carboh ydrates to short-chain (C-2-C-6) fatty acids (SCFAs), is an important function of the large bowel. SCFAs constitute approximately two-thirds of the colonic anion concentration (70-130 mmol/l), mainly as acetate , propionate, and butyrate. Gastroenterologists have, in spite of thes e facts, addressed this scientific field surprisingly late, in contras t to veterinarians, for whom the fermentative production of SCFAs has been acknowledged as a principal mechanism of intestinal digestion in plant-eating animals for decades. Interest in the effects of SCFA prod uction on the human organism has been growing rapidly in the last 10 y ears, because gastrointestinal functions and beneficial effects are as sociated with these acids. SCFAs are of major importance in the unders tanding of the physiological function of dietary fibre and their possi ble role for colonic neoplasia. SCFA production and absorption are clo sely related to the nourishment of the colonic mucosa and sodium and w ater absorption, and mechanisms of diarrhoea. Patients with severe mal absorption compensate by the fermentation of otherwise osmotic active saccharides to SCFAs, which are readily absorbed and used as energy fu els in the organism. SCFA production from dietary carbohydrates is a m echanism whereby considerable amounts of calories can be salvaged in s hort-bowel patients with remaining colonic function if dietary treatme nt is adjusted. SCFA enemas are a new and promising treatment modality for patients with ulcerative colitis. The effect has been attributed to the oxidation of SCFAs in the colonocytes. An impressive number of papers have described the effects of butyrate on various cell function s, the significance of which is still unknown. Up until now, attention has been related especially to cancer prophylaxis and treatment. Dimi nished production of SCFAs appears to be involved in antibiotic-associ ated diarrhoea, diversion colitis, and possibly in pouchitis. The inte raction between bacterial fermentation, ammonia metabolism, and bacter ial growth and protein synthesis appears to be the main mechanism of a ction of lactulose treatment in hepatic coma. Pathological and extreme ly high rates of saccharide fermentation explain the severe deteriorat ion in patients with D-lactate acidosis. Hence, this scientific field has come late to clinical working gastroenterologists, but as work is progressing the production of SCFAs in the large bowel becomes involve d in several well-known intestinal disorders.