Indices of healthy and unhealthy plant-based diets and the risk of selected digestive cancers

Background & aims: The relation between various types of plant-based diets and cancer risk is still unclear. We examined the association of the overall plant-based diet index (PDI) and healthy (hPDI) and unhealthy plant-based diet indices (uPDI) with the risk of selected digestive cancers. Methods: We used data from a network of hospital-based case–control studies including 942 oral/pharyngeal, 304 esophageal, 230 stomach, 1953 colorectal, and 326 pancreatic cancer cases. We calculated PDI, hPDI, and uPDI from a validated food frequency questionnaire. We used multivariable logistic regression models to estimate the odds ratios (OR) of selected digestive cancers across the three indices (in quintiles, Q, or tertiles, T, and in continuous). Results: The PDI was significantly inversely associated with oral/pharyngeal (ORQ5 vs Q1=0.63, 95% confidence interval, CI, 0.47–0.84) and esophageal cancer risk (ORT3 vs T1=0.47, 95% CI 0.31–0.72). The inverse associations appeared stronger for the hPDI (oral cavity/pharynx: ORQ5 vs Q1=0.52; 95% CI 0.39–0.70; esophagus: ORT3 vs T1=0.59, 95% CI 0.39–0.91; stomach: ORT3 vs T1=0.42, 95% CI 0.27–0.67; colorectum: ORQ5 vs Q1=0.69; 95% CI 0.57–0.84; pancreas: ORT3 vs T1=0.60; 95% CI 0.41–0.89). In contrast, the uPDI was directly associated with the risk of oral/pharyngeal (ORQ5 vs Q1=1.43, 95% CI 1.06-1.94), colorectal (ORQ5 vs Q1=2.28, 95% CI 1.86–2.81), and pancreatic cancer (ORT3 vs T1=1.74, 95% CI 1.14–2.65). Esophageal and stomach cancer risks were non-significantly increased by 34% and 46% respectively in the highest uPDI quantile. Conclusion: A plant-based diet, especially a healthy plant-based diet, may reduce the risk of various digestive cancers, whereas an unhealthy plant-based diet may increase the risk. The quality of plant-based diets is important for digestive cancer risk evaluation and prevention.