Influence of diet on colonic fermentation and endogenous formation of N-Nitroso compounds

Background and objectives: High-protein, low carbohydrate diets are popular weight loss regimes. Nonetheless, negative effects on gut health might be expected if less carbohydrate and more protein reach the large intestine, due to shifts in short chain fatty acid (SCFA) patterns and the formation of protein degradation products, including potentially carcinogenic N-nitroso compounds (NOC). Diet is the main driver for endogenous N-nitrosation with red meat being the most important factor, while nitrate and vitamin C also contribute. Previous studies have focused on single dietary components, but to date no study has investigated the combined effect of various dietary components. The aim of the current study was to assess the impact of various dietary components on endogenous formation of NOC and faecal SCFA.
Methods: We conducted three studies in obese men comparing body weight maintenance diets and different high protein weight loss diets. Dietary intakes were estimated from food diaries and correlated with faecal fermentation products and NOC. We studied the effect of protein components (total protein, total meat, red and white meat), carbohydrate components (total carbohydrates, digestible and non-digestible carbohydrates), and vitamin C and nitrate on NOC.
Results: We observed that shifts in the dietary carbohydrate/protein ratio resulted in alterations in faecal SCFA patterns. Furthermore, using random effects multiple linear regression, we confirmed red meat as the strongest contributor to endogenous NOC formation, but nitrate, vitamin C, non-starch polysaccharides and total energy also played a significant role.
Conclusion: We have identified the contributions of various dietary components to endogenous NOC formation and formulated a prediction model for NOC formation in obese men, based on their dietary intakes. This model could improve the estimation of endogenous NOC formation in epidemiological studies into diet and cancer, which is currently based on red meat intake only.