Browsing by Subject "kolorektal cancer"

Background and aim: Colorectal cancer is the fourth most common form of cancer in the world and the third most common in Finland. One third of the cases are supposed to origin from lifestyle factors. Some studies have even suggested that as much as 30 - 70 % of the cases can originate from the diet. A diet with a smaller amount of red and processed meat has in some studies been associated to a smaller risk for developing colorectal cancer. Processed meat is considered to have a convincing connection to colorectal cancer and red meat is considered to have a possible connection. A possible explanation to this can be the formation of N-nitroso compounds (NOC) which arises from red meat. NOCs are considered to be potentially cancer-causing compounds, when they come in contact with the surface of the intestine. The aim of this study was to examine whether there is a difference in the amount of NOCs in the faeces among healthy humans, when replacing proteins from animal sources in the diet with an equal amount of proteins from plant sources. Material and methods: This thesis is a part of the study ScenoProt at the University of Helsinki. ScenoProt examines which effect diets with different types of protein sources have on markers for health. The study was conducted in 2017 as a controlled clinical intervention study with parallel and randomized design. The participants were voluntary healthy humans between the ages of 20 and 69 years. The intervention period lasted 12 weeks and the participants were allocated into three different diet groups. In group 1 (n=48) the amount of protein in the diet consisted of 70 % animal proteins and 30 % plant proteins, in group 2 (n=48) 50 % animal proteins and 50 % plant proteins and in group 3 (n=49) 30 % animal proteins and 70 % plant proteins. Faecal samples were collected before the intervention period and during its last week. The participants kept a food diary four days before the intervention period, four days during its last week and 1 day/three weeks during its time. Faecal samples were analysed for the amount of N-nitroso compounds, N-haem compounds and N-thiol compounds with a NO-analyser that measures the nitrogen oxide released from nitrogen compounds. The statistical analyses were carried out with IBM SPSS Statistics. Variance analysis between groups were carried out with Bonferroni test and correlation was examined with Pearson test. As the limit for statistical significance, <0,05 was used. Results: 136 participants, 107 women and 29 men, completed the study. A dose-dependent decrease in total NOC concentration was observed between the groups (group 1: 4,0 ± 2,4, group 2: 3,2 ± 1,8, group 3: 2,7 ± 1,5 pmol/mg). There was a significant difference in the amount of N-nitroso compounds (p=0,000), N-haem compounds (p=0,000) and N-thiol compounds (p=0,030) between groups 1 and 3 at the end of the intervention. A significant difference in N-haem compounds (p=0,035) was also observed between groups 2 and 3. The amount of protein in the diet didn’t correlate with the amount of NOC in the faeces (p=0,622), whereas the total intake of fibre did correlate with the amount of NOC (0,036). The faecal weight increased gradually from groups 1 to 3 and the weight correlated with the amount of fibre (p=0,000) in the diet and the amount of NOC (p=0,000). Conclusion: A replacement of animal proteins with plant proteins in the diet leads to a dose-dependent decrease in the amount of NOC in the faeces. A diet with a greater amount of plant proteins and a smaller amount of animal proteins might therefore protect against the development of colorectal cancer. The increased amount of fibre in a plant protein-based diet might to some extent contribute to the decrease in NOC, since fibre in some cases has been seen to decrease the formation of NOC. Seen to previous studies, it is however most likely that the decrease in NOC is mostly attributed to the differences in protein sources.