Does the biomarker 15N-lactose ureide allow to estimate the site of fermentation of resistant starch?
We evaluated the effect of resistant starch (RS) and resistant starch with wheat bran (RS+WB) on the colonic ammonia metabolism in healthy volunteers using the biomarker 15N-lactose ureide (15N-LU). Particularly, it was investigated whether this biomarker allowed to estimate differences in the site of fermentation. Ten volunteers were included in a placebo-controlled crossover study. They consumed in random order 2 × 15 g RS/day for 2 weeks and placebo for 2 weeks separated by 2 weeks wash-out. At baseline, on the first day of each intake period and after each intake period, they consumed a 15N-labelled test meal and collected all urine in different fractions for 48 h. In ten other volunteers, the effect of 2 × 15 g RS/day and of 2 × 15 g RS + 2 × 6 g WB was compared. These volunteers collected urine and feces for 72 h. 15N-content of urine and feces was measured using combustion-isotope ratio mass spectrometry. RS exerted a significant decrease in cumulative urinary 15N-excretion which was different from placebo. The effect was most pronounced in the 6–24 h urine fraction which suggest fermentation in the proximal colon. The effect of RS+WB on cumulative urinary 15N-excretion was not significantly different from the effect of RS. A less pronounced decrease in the 6–24 h fraction was observed suggesting less fermentation in the proximal colon whereas no indications for more distal fermentation were observed. Since about 80% of the cumulative urinary 15N was recovered within 24 h, it was concluded that the biomarker 15N-LU was useful to monitor processes in the proximal colon rather than in the distal colon.
Keywordsstable isotope prebiotic wheat bran resistant starch site of fermentation
The present study was carried out with financial support from the Commission of the European Communities, specific RTD programme “Quality of Life and Management of Living Resources”, QLK1-2001-00431 “Stable isotope applications to monitor starch digestion and fermentation for the development of functional foods”. It does not necessarily reflect its views and in no way anticipates the Commission’s future policy in this area.
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