The effect of haem in red and processed meat on the endogenous formation of N-nitroso compounds in the upper gastrointestinal tract.
Level 2 - randomized trial
Individual randomized crossover dietary trial in human participants
PubMed 17052997 · doi:10.1093/carcin/bgl192
What was done
In a randomized crossover intervention conducted in a volunteer suite, 27 ileostomists consumed three diets: no meat, 240 g red meat (RM), or 240 g processed meat (PM). Endogenous N-nitroso compounds (NOCs) were measured as apparent total N-nitroso compounds (ATNC) in ileostomy output. The effects of supplementation with 1 g ascorbic acid or 400 IU alpha-tocopherol were also tested, along with complementary in vitro nitrosation experiments involving haemoglobin at pH 6.8.
What was found
Dietary ATNC concentrations were 9 microg/kg in the no-meat diet, 22 microg/kg in RM, and 37 microg/kg in PM. ATNC concentrations in ileostomy output increased significantly from 283 microg/kg (SEM = 74) on the no-meat diet to 1175 microg/kg (SEM = 226, P = 0.001) following RM and 1832 microg/kg (SEM = 294, P < 0.001) following PM. Supplementation with ascorbic acid or alpha-tocopherol had no effect on ileal ATNC concentrations. In vitro, N-nitrosomorpholine formed in the presence of nitrosated haemoglobin at pH 6.8, but not in its absence.
Why it matters
This study demonstrates that endogenous formation of potentially carcinogenic N-nitroso compounds driven by red and processed meat can occur in the human upper gastrointestinal tract independently of colonic bacterial fermentation.
Limits
The study evaluated a small sample of 27 individuals with ileostomies, whose gastrointestinal physiology and transit may differ from individuals with an intact colon. The primary outcome was a surrogate biochemical marker (ATNC) rather than clinical cancer outcomes, and antioxidant testing was limited to single doses of ascorbic acid and alpha-tocopherol.
Cited by
- contradicts Eating vitamin C-rich foods with unprocessed red meat substantially mitigates the formation of harmful compounds in the human gut.
- supports Nitrates added to processed meat form potentially carcinogenic compounds in the human gut to a significantly greater degree than unprocessed red meat.