effect of pre- and probiotics on the colonic ammonia metabolism in humans as measured by lactose-[15N2]ureide

Background: The evaluation of ammonia detoxification by pre- and probiotics by means of colonic lactose-[15N2]ureide (15N-LU) degradation is of great interest both scientifically and in terms of nutrition physiology. Objective: Pre- and probiotics were supplemented in healthy adults to evaluate the effect of the ammonia metabolism in the human colon by means of 15N-LU. Methods: A total of 14 participants aged 20–28 years daily received a regular diet either without (no treatment) or with supplementation of 30 g fibre of potatoes (FPs), 30 g wrinkle pea starch (WPS, resistant starch content: 12 and 70%, respectively) and 375 g Lactobacillus acidophilus (LC1) yoghurt, over a 10-day period in a randomised order. After 1 week, 5.7 mg/kg body weight 15N-LU was administered together with breakfast. A venous blood sample was taken after 6 h. Urine and faeces were collected over a period of 48 and 72 h, respectively. The 15N abundances were measured by isotope ratio mass spectrometry. Results: The mean renal 15N-excretion differed significantly between the supplementation of FP and no treatment (32.5 versus 46.3%, P=0.034), FP and LC1 (32.5 versus 51.6%, P=0.001), and WPS and LC1 (38.5 versus 51.6%, P=0.048). The mean faecal 15N-excretion amounted to 42.7% (no treatment), 59.7% (FP), 41.8% (WPS) and 44.0% (LC1). In comparison with no treatment, the urinary 15NH3-enrichment was significantly decreased at 16 h after FP supplementation. Conclusion: The prebiotic intake of FP and WPS lowered the colonic generation and the renal excretion of toxic 15NH3, respectively, when using 15N-LU as a xenobiotic marker.