Background
Colorectal cancer is a major global health concern. Diet plays a critical role, with processed meat (PM) as a significant risk factor. Based on experimental and epidemiological evidence, the International Agency for Research on Cancer has classified PM as carcinogenic to humans (Group 1). Among the additives largely used in curing, nitrite and nitrate salts improve microbial safety and oxidative stability of PM but can lead to the formation of carcinogenic N-nitroso compounds (NOCs). In France, a national action plan has set a target level of 90 ppm in PM, based on recent experimental evidence from our team. These results demonstrated that reducing or eliminating nitrites in cooked PM protects against colorectal carcinogenesis promotion in a rat model, even if elimination offers no greater benefit than reduction. While removal prevents NOCs formation, it also results in a strong increase in genotoxic lipid peroxidation end-products.

Objectives
This project aims, as part of public policy support, to assess the impact of nitrite reduction (at the old and regulatory levels, but also lower doses) and elimination on two categories of largely consumed processed meat. Both NOCs and lipid peroxidation biomarkers were quantified to determine the lowest nitrite dose that significantly reduces NOCs without increasing lipoperoxidation.

Methods
A 22-day in vivo nutritional study was conducted using Fischer 344 rats (n = 40; 8 per group) to investigate the effects of consumption of pork and poultry ham produced with different levels of sodium nitrite: 0, 60, 80, and 120 ppm. The control group received the AIN-76 standard diet, and all experimental diets were isocaloric and balanced. Fecal, urinary, and colon tissue samples were collected and assessed for heme content, NOCs (via ATNC), and lipid peroxidation end products (via fecal TBARS and urinary 1,4-dihydroxynonane mercapturic acid (DHN-MA)). Endpoints also include the cytotoxicity and genotoxicity of rats’ fecal water.

Results
As expected, the fecal NOCs profile was nitrite dose-dependent for both product types, but with a two-fold increase in NOCs concentration with pork ham consumption compared to poultry ham. Associated with this difference in fecal ATNC, fecal heme (a known catalyzer of nitrosylation) was higher in pork ham groups. Regarding lipid peroxidation in pork ham groups, only withdrawal induced an increase in fecal peroxidation (TBARS; p < 0.0001), while DHN-MA was significantly increased from 80 ppm. For poultry ham groups, neither reduction nor withdrawal alters fecal peroxidation, but DHN-MA increased (p < 0.0001) after withdrawal. Fecal water cytotoxicity was higher following pork ham consumption, with histological evidence of colonic genotoxicity.

Conclusion/Implications for policy
Our results show that reducing or eliminating nitrites decreases consumer exposure to NOCs. Reduction to 80 ppm significantly lowered exposure without increasing fecal peroxidation, while further reductions increased peroxidation, particularly in heme-rich PM (pork ham). Elimination induced significant peroxidation in both PM types, leading to the formation of genotoxic end-products. Process modifications would be required to control this formation. Importantly, any further reduction strategy must also account for microbiological safety, even though reduced nitrite levels are found to be sufficient under controlled conditions.