Plant-Based Diet Quality and Gastric Cancer Risk: A Case-Control Study in High-Risk Regions of Fujian Province, China

Plant-based diets have been increasingly associated with cancer prevention, but the distinct impacts of healthy and unhealthy plant-based foods on gastric cancer (GC) risk remain uncertain. This study aimed to investigate the associations of the overall plant-based dietary index (PDI), the healthy PDI (hPDI), and the unhealthy PDI (uPDI) with GC risk. A sex-matched case-control study was carried out in Fujian, China, between July 2023 and November 2024, including 336 newly diagnosed GC patients and 336 community controls. Dietary intake was evaluated using a validated food frequency questionnaire. In total, 672 participants (56.5% male) were analyzed, with cases being older than controls (mean age 56.76 vs. 53.86 years, p < 0.001). Higher PDI was associated with a lower risk of GC (Q4 vs. Q1: OR = 0.55, 95% CI: 0.35-0.84, p for trend = 0.001). For hPDI, the highest versus lowest quartile comparison suggested an inverse association (OR = 0.63, 95% CI: 0.41-0.96), although the trend test was marginally significant (p for trend = 0.069). Each 1-SD increase in PDI was associated with a 26% lower risk of GC (OR = 0.74, 95% CI: 0.63-0.87, p < 0.001). Conversely, higher uPDI was associated with a markedly increased risk (OR = 2.42, 95% CI: 1.55-3.78, p for trend < 0.001), with each 1-SD increase associated with a 56% higher odds of GC (OR = 1.56, 95% CI: 1.33-1.85, p < 0.001). Subgroup analyses suggested that the inverse associations of PDI and hPDI with GC risk were more pronounced among smokers and individuals reporting low life stress, while the positive association of uPDI with GC risk appeared stronger in younger and married participants. Greater adherence to overall and healthy plant-based diet patterns was associated with a lower risk of GC, whereas higher adherence to unhealthy plant-based patterns was associated with a higher risk. These findings suggest that promoting higher-quality plant-based eating habits may be beneficial for GC prevention, particularly in high-risk populations.