title: Effect of vegetables, tea, and soy on endogenous N-nitrosation, fecal ammonia, and fecal water genotoxicity during a high red meat diet in humans.
abstract: Red meat increases colonic N-nitrosation, and this may explain the positive epidemiological relationship between red meat intake and colorectal cancer risk. Vegetables, tea, and soy have been shown to block N-nitroso compound (NOC) formation and are associated with protection against colorectal cancer. To determine whether these supplements affect fecal NOC excretion during consumption of a high red meat (420 g/day) diet, 11 male volunteers were studied over a randomized series of 15-day dietary periods. Seven of these subjects completed a further dietary period to test the effects of soy (100 g/day). Soy significantly suppressed fecal apparent total NOC (ATNC) concentration (P = 0.02), but supplements of vegetables (400 g/day as 134 g broccoli, 134 g brussels sprouts, and 134 g petits pois) and tea extract (3 g/day) did not affect mean levels of fecal ATNC, nitrogen and ammonia excretion, and fecal water genotoxicity. However, fecal weight was increased (P < 0.001) and associated with reduced transit time (r = 0.594, P < 0.0001), so that contact between ATNC, nitrite, and ammonia and the large bowel mucosa would have been reduced. Longer transit times were associated with elevated fecal ATNC concentrations (r = 0.42, P = 0.002). Fecal nitrite was significantly suppressed during the tea supplement compared with the meat-only (P = 0.0028) and meat + vegetables diets (P = 0.005 for microgram NO2/g).
authors.affiliation: Dunn Human Nutrition Unit, Medical Research Council, Cambridge CB2 2XY, UK.
authors.forename: Roisin
authors.initials: R
authors.lastname: Hughes
authors.forename: Jim R A
authors.initials: JR
authors.lastname: Pollock
authors.forename: Sheila
authors.initials: S
authors.lastname: Bingham
mesh_terms: D000328:Adult; D000641:Ammonia / Q000378:metabolism*; D003106:Colon / Q000502:physiology; D004249:DNA Damage; D004032:Diet; D005243:Feces / Q000737:chemistry; D006801:Humans; D008460:Meat; D008875:Middle Aged; D015538:Nitrosation; D013025:Glycine max; D013662:Tea; D014675:Vegetables; D014867:Water
chemical_list: D013662:Tea; D014867:Water; D000641:Ammonia