Oats have a high content of soluble fibre in the form of β-glucan, but contain also arabinoxylans and cellulose which are mainly insoluble fibre. The fibres are not digested in the small intestine, but the soluble β -glucan is believed to increase the viscosity of the food bolus, leading to a slower gastric emptying, enhanced gut fill, and slower absorption of nutrients. β-glucans are highly susceptible to microbial attack and the intestinal flora harbouring the small intestine can modify the molecular weight and viscosity elevating properties.
In the large intestine β-glucans are readily fermented by bacteria colonizing the caecum and upper colon. Cellulose and arabinoxylans are much more slowly degraded and to a much lower extent. The degradation of the fibre components leads to increased microbial activity and the production of short-chain fatty acids and various gases. While the insoluble fibre reduces transit time and increases faecal wet weight by means of its physical presence, soluble fibre operates through an increase in microbial cells mass. Oats have been shown to increase the proportion of butyrate, which has regulatory functions in cell proliferation and differentiation. β-glucan, however, leads mainly to the production of propionate, which is suggested as one of the mechanisms for the cholesterol lowering effects of oats and other β-glucan containing products. Recently it was concluded that β-glucans have no prebiotic potential.
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