Norway exhibits one of the highest rates of colorectal cancer (CRC) in the world, and several dietary factors have been associated with the risk of CRC. With higher consumption of ultra-processed foods (UPF), a better understanding of how food processing affects CRC might be a new approach for prevention. The current findings are contradictory, and new findings indicate that CRC risk factors might affect colorectal subsites differently. We wanted to study the association between intake of UPF and CRC risk in Norwegian women. In this prospective cohort analysis encompassing 77 100 women (1625 cases) from the Norwegian Women and Cancer study, dietary intakes were collected using validated semi-quantitative FFQ and categorised using the Nova classification system. Multivariable Cox proportional hazard models were used to assess the association between intake of UPF and CRC risk. The average follow-up time was 17·4 years. A high UPF intake (fourth quartile), compared with a low UPF intake (first quartile), was statistically significantly associated with increased total CRC risk after adjusting for all covariates and energy intake (hazard ratio (HR) = 1·24; 95 % CI 1·04, 1·49, Pfor trend = 0·02). Furthermore, a high UPF intake, compared with a low UPF intake, was statistically significantly associated with right-sided colon cancer (HR = 1·58; 95 % CI 1·19, 2·09, Pfor trend < 0·001). More research is needed to understand the associations between UPF, UPF subgroups and total CRC as well as cancer in colorectal subsites.

Recent studies have shown a decreased risk of colon cancer with consumption of fish. However, most studies on fish consumption do not distinguish between lean and fatty fish, or between poached and fried fish. The aim of this study was to investigate any association between fish consumption and colon cancer in The Norwegian Women and Cancer (NOWAC) study. We focused mainly on lean fish, which was further divided into poached and fried fish. A total of 63 914 women were included in the analysis, 254 of whom were found to have colon cancer during follow-up. Since fish consumption was one of the main topics of interest in the NOWAC study, there is a predominance of women from northern Norway due to higher fish intake in this area; hence the study is not representative of the whole of Norway. The participants completed a semi-quantitative FFQ between 1996 and 1999, and were followed-up for incidence of colon cancer until 2004. No association between fish consumption and risk of colon cancer was seen, except for the third tertile of poached lean fish consumption (relative risk (RR) 1·46, 95 % CI 1·04, 2·06). This association disappeared when excluding women with less than 1 year of follow-up. In conclusion, the present study does not support the hypothesis of a protective effect of fish against colon cancer risk.