Association of Body Mass Index and Plant-Based Diet with Cognitive Impairment among Older Chinese Adults: A Prospective, Nationwide Cohort Study

= 0.005 for nonlinearity). Participants who were overweight (HR = 0.79; 95% CI 0.66-0.95) and obese (HR = 0.72; 95% CI 0.54-0.96) had a decreased risk of cognitive impairment, while those who were underweight (HR = 1.42; 95% CI 1.21-1.66) had an increased risk. Lower PDI, lower hPDI, and higher uPDI were associated with an increased risk of cognitive impairment (HR = 1.32; 95% CI 1.16-1.50 for PDI; HR = 1.46; 95% CI 1.29-1.66 for hPDI; HR = 1.21; 95% CI 1.06-1.38 for uPDI). The protective effect of being overweight on cognitive impairment was more pronounced among participants with a higher PDI (HR = 0.74; 95% CI 0.57-0.95) than those with a lower PDI (HR = 0.87; 95% CI 0.67-1.12), among participants with a higher hPDI (HR = 0.73; 95% CI 0.57-0.94) than those with a lower hPDI (HR = 0.93; 95% CI 0.72-1.10), and among participants with a lower uPDI (HR = 0.61; 95% CI 0.46-0.80) than those with a higher uPDI (HR = 1.01; 95% CI 0.80-1.27). Our results support the positive associations of overweight status, obesity, an overall PBD, and a healthful PBD with cognitive function in older adults. A lower adherence to an overall PBD, a healthful PBD, and a higher adherence to an unhealthful PBD may attenuate the protective effect of being overweight on cognitive function.