Plant-based diet and survival among patients with metastatic colorectal cancer

Background: A plant-based diet is associated with better survival among patients with nonmetastatic colorectal cancer (CRC), but its association in metastatic CRC is unknown. Methods: Using an National Cancer Institute–sponsored trial (CALGB/SWOG 80405), we included 1284 patients who completed validated food frequency questionnaires at the initiation of metastatic CRC treatment. We calculated 3 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 3 indices (quintiles) with overall survival (OS) and progression-free survival (PFS) using multivariable Cox proportional hazards regression. Results: We observed 1100 deaths and 1204 progression events (median follow-up ¼ 6.1 years). Compared with the lowest quintile, patients in the highest quintile of PDI had significantly better survival (hazard ratio [HR] for OS ¼ 0.76 [0.62-0.94], P_trend ¼ .004; PFS ¼ 0.81 [0.66-0.99], P_trend ¼ .09). Similar findings were observed for hPDI (HR for OS ¼ 0.81 [0.65-1.01], P_trend ¼ .053; PFS ¼ 0.80 [0.65-0.98], P_trend ¼ .04), whereas uPDI was not associated with worse survival (HR for OS ¼ 1.16 [0.94-1.43], P_trend ¼ .21; PFS ¼ 1.12 [0.92-1.36], P_trend ¼ .42). Conclusions: Our study suggests that a 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.