Effect of vegetables, tea, and soy on endogenous N-nitrosation, fecal ammonia, and fecal water genotoxicity during a high red meat diet in humans

Nutr Cancer. 2002;42(1):70-7. doi: 10.1207/S15327914NC421_10.


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).

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Ammonia / metabolism*
  • Colon / physiology
  • DNA Damage*
  • Diet
  • Feces* / chemistry
  • Humans
  • Meat*
  • Middle Aged
  • Nitrosation*
  • Soybeans*
  • Tea*
  • Vegetables*
  • Water


  • Tea
  • Water
  • Ammonia