Abstract 965: Effects of replacing dietary animal protein with plant-based protein on the formation of intestinal N-nitroso compounds (NOCs) and biomarkers of colon cancer in healthy adults–a 12-week intervention study

Epidemiological studies have indicated that high consumption of red and processed meats and low consumption of fiber-rich and plant-based foods are associated with an increased risk for colorectal cancer. Here we aimed to investigate whether partial replacement of dietary animal proteins with plant-based proteins changes gut metabolism and markers for colon cancer risk. We carried out a 12-week partly controlled clinical intervention study with following diets: 1) 70% of proteins from animal-based sources and 30% from plant-based sources, representing habitual Finnish/Western diet at the moment 2) 50% animal and 50% plant-based protein sources and 3) 30% animal and 70% plant-based proteins. Protein intake on all diets was planned to be 17 E% and the actual intake was analyzed using 4-day food records before and at the end of the intervention. Healthy, 20-69-year old participants (n=136) were randomly allocated to intervention groups. Participants collected stool samples before and at the end of the intervention. Fecal water was extracted and its effect on the viability of human colon carcinoma cells after 24h exposure was determined using cck-8 reagent. A 1:5 fecal homogenate was prepared and analyzed for total and heme-derived NOCs using selective de-nitrosation and detection by Ecomedics CLD 88 Exhalyzer. A separate spot stool sample was collected for gut microbiota analyses. At the end of the intervention, the viability of HCA7 colon carcinoma cells exposed to fecal water was significantly lower (P=0.005 ANCOVA) in the most plant-based diet group in comparison to group 1 (29.9% vs. 37.7%, P=0.011) and group 2 (29.9% vs. 37.1%, P=0.021). The concentrations of total NOCs (groups 1: 4.0 ± 2.4, 2: 3.1 ± 1.8, 3: 2.7 ± 1.5 pmol/mg faeces; 1 vs. 2 P=0.056, 1 vs. 3 P=0.001) and heme-derived NOCs (1: 2.5 ± 1.9, 2: 1.8 ± 1.4, 3: 1.4 ± 0.9 pmol/mg faeces; 1 vs. 2 P=0.055, 1 vs. 3 P