Plant-Based Diet and Survival Among Patients with Metastatic Colorectal Cancer

Background Plant-based diet is associated with better survival among patients with non-metastatic colorectal cancer (CRC), but its association in metastatic CRC is unknown. Methods Using an NCI-sponsored trial (CALGB/SWOG 80405), we included 1,284 patients who completed validated food frequency questionnaires at the initiation of metastatic CRC treatment. We calculated three indices: overall plant-based diet index (PDI), which emphasized consumption of all plant foods while reducing animal food intake; healthful plant-based diet index (hPDI), which emphasized consumption of healthful plant foods such as whole grains, fruits, and vegetables; and unhealthful plant-based diet index (uPDI), which emphasized consumption of less healthful plant foods such as fruit juices, refined grains, and sugar-sweetened beverages. We estimated the associations of three indices (quintiles) with overall survival (OS) and progression-free survival (PFS) using multivariable Cox proportional hazards regression. Results We observed 1,100 deaths and 1,204 progression events (median follow-up: 6.1 years). Compared to the lowest quintile, patients in the highest quintile of PDI had significantly better survival (HR for OS: 0.76 [0.62-0.94], P trend=0.004; PFS: 0.81 [0.66-0.99], P trend=0.09). Similar findings were observed for hPDI (HR for OS: 0.81 [0.65-1.01], P trend=0.053; PFS: 0.80 [0.65-0.98], P trend=0.04), whereas uPDI was not associated with worse survival (HR for OS: 1.16 [0.94-1.43], P trend=0.21; PFS: 1.12 [0.92-1.36], P trend=0.42). Conclusions Our study suggests that plant-based diet, especially when rich in healthful plant foods, is associated with better survival among patients with metastatic CRC. The cause of survival benefits warrants further investigation.