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Knowledge about the influence of resistant starch on colonic nitrogen metabolism

Fermentation of carbohydrates in the large bowel results in the formation of short chain fatty acids which have generally been accepted to be beneficial to the host whereas fermentation of proteins gives rise to the production of potentially toxic metabolites such as ammonia, phenols, thiol compounds and amines. Most dietary interventions targeting the colon aim at increasing the saccharolytic activity of the colonic microbiota and decreasing the proteolytic activity. We have developed a non-invasive strategy based on stable isotope technology and focussing on the metabolite ammonia to measure quantitatively the influence of non-digestible carbohydrates on the metabolic processes occurring in the colon.

After oral administration, the biomarker lactose [15N,15N] ureide is hydrolysed upon arrival in the colon and yields 15NH3 which can be assimilated by the microbiota followed by faecal excretion or can be absorbed through the colon mucosa followed by urinary excretion of 15N. We have shown that the presence of resistant starch (type 3) in the colon resulted in a significant reduction of urinary 15N-excretion and an increase in faecal 15N, indicating that resistant starch efficiently stimulates bacterial activity and removes in this way the toxic metabolite ammonia from the colonic lumen. Secondly, we have shown that administration of resistant starch combined with wheat bran resulted in a less extensive effect in the proximal colon. However, it was not possible to confirm a shift of the site of fermentation to more distal parts of the colon. The technology is also applicable to other fermentable carbohydrates and allows comparative and quantitative evaluation of so-called prebiotic substrates.

Reported by

Laboratory Digestion & Absorption - Katholieke Universiteit Leuven
UZ Gasthuisberg E462, Herestraat 49
3000 Leuven
Belgium
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