The association between Planetary Health Diet Index and the risk of colorectal cancer: a case-control study

Background Despite the beneficial effects of a plant-based diet on colorectal cancer (CRC), no study has yet investigated the relationship between a Planetary Health Diet Index (PHDI) and CRC in the Iranian population. Therefore, the present case-control study aimed to assess the relationship between this index and CRC. Methods The current research was conducted on 71 patients with CRC (case group) and 142 (control group) admitted to hospitals in Tehran, Iran. The PHDI (0-150 points) was calculated based on a semi-quantitative food frequency questionnaire. Conditional logistic regression was applied to evaluate the association between CRC and PHDI and its sub-scores. Results After adjusting for the role of potential confounders, lower odds of CRC were observed in the second tertile of the total ratio score (odds ratio (OR) = 0.334; 95% confidence interval (CI): 0.127-0.878, P = 0.026) and the last tertile of PHDI (OR = 0.407; 95% CI: 0.183-0.907, P = 0.028), total adequacy score (OR = 0.261; 95% CI: 0.110-0.622, P = 0.002), and total moderation score (OR = 0.380; 95% CI: 0.162-0.891, P = 0.026) in comparison to the first tertile of each index. Conclusions The current study's findings indicated a reverse relationship between PHDI, total adequacy, moderation, and ratio scores with the CRC odds. However, it is suggested that more research be performed in this field in the future to confirm the results of this study.