Association Between Plant-based Diet and Risk of Colorectal Cancer: Findings from the Singapore Chinese Health Study

Colorectal cancer (CRC) is a leading malignancy worldwide. Diet is one of the major modifiable risk factors for CRC. However, little is known about the relationship between a plant-based diet and CRC risk in the Asian population. This study aimed to evaluate the association between two pre-defined plant-based dietary indices and the risk of CRC in a Chinese Singaporean population, using data from the Singapore Chinese Health Study (SCHS). SCHS is an ongoing prospective cohort study among 63,257 Chinese Singaporeans, aged 45-74, who were enrolled between the years of 1993-1998. Dietary information was obtained using a semi-quantitative food frequency questionnaire (FFQ), containing 165 food items commonly consumed by the Chinese population living in Singapore. Two plant-based dietary indices were constructed such as overall plant-based diet index (PDI) and the healthy plant-based diet index (hPDI). Cox proportional hazard regression model was used to obtain multivariable hazard ratios (HRs) and their 95% confidence intervals (CIs) of CRC incidence across these two plant-based diet indices after controlling for different confounding factors (i.e., age, sex, smoking status, alcohol drinking status, history of diabetes, family history of CRC, and total energy intake). During an average of 17.5 years of follow-up, we identified 2,140 incident cases of CRC. We found that for the highest adherence of hPDI, there was a 6% reduction in the risk of CRC, compared to those in the lowest adherence of hPDI (HR=0.94, 95% CI: 0.83-1.06, Ptrend= 0.26). This result was not statistically significant. A similar pattern was observed between PDI and CRC risk (HR=0.88, 95% CI: 0.77-1.00, Ptrend= 0.08), suggesting a 12% decrease for CRC risk in the highest PDI quartile compared to the lowest, however this result is not statistically significant. In a prospective cohort of more than 63,000 Chinese Singaporeans, we did find inverse associations between PDI and hPDI with risk of CRC. Our findings have great implications for public health significance as it helps to create targeted interventions for prevention and control of CRC risk in Asian populations.