Production and digestive effects of short chain fatty acids.

The major organic anions in the large bowel are short-chain fatty acids (SC FAs) yielded by fermentation of carbohydrates. Production of SCFAs depends on several closely related factors, but can be mainly attributed to the nat ure of the substrates, the composition and activity of microflora, and envi ronmental conditions in the intestinal lumen. The major SCFAs, namely aceta te, propionate and butyrate, are rapidly absorbed by the colonic mucosa. Bu tyrate is oxidised in colonocytes and yields about 70% of their energetic r equirements. SCFAs modulate gastro-intestinal motility, are trophic factors for the epithelium and may stimulate mucosal defences. In contrast to its effect on healthy mucosal butyrate inhibits proliferation and increases dif ferentiation of cancerous cells. The mechanisms of action of SCFA are still incompletely understood, although cellular, hormonal and nervous effects a re involved. SCFA could be used as prophylactic or therapeutic agents, for instance in the treatment of diarrhoeas or certain forms of inflammatory bo wel diseases. In addition, butyrate has been shown to be protective against cole-rectal cancer in experimental animal models.