Associations between protein source and colorectal cancer risk in a prospective cohort of Norwegian women

Background
Colorectal cancer (CRC) is the third most common cancer worldwide, and it is particularly prevalent in the Nordic countries. The high global burden of CRC and increasing incidence rates among younger adults are trends that warrant more high-quality research into underlying risk factors. Approximately half of all CRC cases can be attributed to modifiable risk factors such as lifestyle and diet, and the International Agency for Research on Cancer classifies red meat as probably carcinogenic and processed meat as carcinogenic to humans. One proposed mechanism involves the effects of protein fermentation metabolites on the colonic epithelium and gut microbiota. Proteins from different food sources vary in structure, function, and nutritional characteristics. Therefore, there is a need to consider dietary protein source when evaluating the relationship between diet and CRC.
 
Objectives
The primary objective of this study is to investigate the role of dietary protein source with regard to CRC risk in a large cohort of Norwegian women. Specifically, we aim to examine whether animal- and plant-derived proteins are differentially associated with CRC incidence.
 
Methods
We will analyse data from the Norwegian Women and Health Study (NOWAC), a population-based longitudinal cohort consisting of over 172,000 Norwegian women, established in 1991 to investigate cancer risk factors. Dietary data were collected using validated food frequency questionnaires (FFQs). Estimation of the percentage contribution of animal and plant protein to total protein intake from FFQ data is currently underway. CRC incidence data were obtained from the Cancer Registry of Norway. We will examine the relationship between dietary protein source and CRC incidence using Cox proportional hazards regression. To test the hypothesis that protein source influences CRC risk, multivariable-adjusted hazard ratios (HRs) for CRC incidence across quantiles of animal and plant protein intake will be estimated. Additionally, potential dose-response relationships will be investigated, and isocaloric substitution models will be applied to estimate the effect of substituting an equal amount of energy from animal protein with plant protein.
 
Results
A total of 95,917 participants from NOWAC, including 2,705 CRC cases, have been included in our study. Data analysis is ongoing; results will be available by May and reported at the conference. We will present HRs for CRC risk according to intake levels of animal and plant protein, including dose–response patterns and substitution effects.
 
Conclusions/Implications for practice or policy
This research is expected to elucidate the role of dietary protein source as a risk factor for CRC and generate new knowledge that may inform dietary guidelines and public health policies. By examining dietary shifts that may lower cancer risk, this work is relevant for actionable cancer prevention strategies.