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Basic concepts / Prebiotics
Prebiotics
As the commercial prebiotic oligosaccharides increase colonic carbohydrate fermentation, they also increase gas formation(2,3). This means that the main side effects are flatulence and bloating, but they depend on the type of oligosaccharide and the tolerance of the host.
The gas H2S is very reactive and can have negative effects on the intestine. The other gases, hydrogen (H2), CO2 and methane (CH4) have no negative effects, except flatulence and bloating. SCFA and lactate are beneficial for both the intestinal microflora (lowering of the pH, making the intestine more acidic) and the intestinal cells (which need SCFA for energy). Ethanol is rapidly metabolised by other intestinal bacteria and has no effect on the host. BCFA, ammonia (NH3), amines, phenols and indoles are irritants to the intestinal cells or may have a negative effect on the immune system at high concentrations(2).
Figure 1. Schematic fermentation of protein and carbohydrates by the intestinal microflora. Protein and fermentation products mainly derived from protein fermentation are underlined(2).
SCFA = Short Chain Fatty Acids, BCFA = Branched Chain Fatty Acids.
1. Gibson G.R., Roberfroid M.B. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics.
J Nutr. 1995 Jun; 125(6): 1401-1412.
2. Gibson G.R., Beatty E.R., Wang X. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 1995; 108: 975–982.
3. Rycroft C.E., Jones M.R., Gibson G.R. A comparative in vitro evaluation of the fermentation properties of prebiotic oligosaccharides. J Appl Microbiol 2001; 91 (5): 878-887.
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