Adherence to a Planetary Health Diet, Diet-related Greenhouse Gas Emissions, Functional Disability, and Mortality in Older Adults

BACKGROUND: Previous epidemiological studies have revealed a relationship among planetary health diets (PHDs), diet-related greenhouse gas emissions (GHGEs), and mortality. However, these studies did not include older adults from non-Western countries. This study examined these associations in Japanese older adults. METHODS: This prospective study included 8, 043 adults aged ≥65 years from the Kyoto-Kameoka study in Japan. Dietary intake was estimated using a validated food frequency questionnaire. Adherence to PHDs was evaluated by calculating the EAT-Lancet index (range, 0 [worst] to 42 [best]), which were classified into 4 categories: ≤25 (n = 1 061; very low), 26-27 (n = 1 703; low), 28-30 (n = 3 368; moderate), and ≥31 (n = 1,911; high) points. Diet-related GHGEs were calculated using previously developed GHGE tables for each food item. RESULTS: During the median 4.75-year follow-up period, 659 deaths and 1 431 incidents of functional disability were recorded. After adjusting for confounders, the hazard ratios of mortality were lower in the moderate-adherence group than in the very low-adherence group (hazard ratio, 0.64; 95% confidence interval; 0.60-0.93). Planetary health diet scores tended to be inversely associated with functional disability (p for trend = .081). However, diet-related GHGEs were not associated with mortality or disability. The PHD score ranges with the lowest hazard ratios for mortality and mean diet-related GHGE were 28-30 and 29-31 points, respectively. CONCLUSIONS: Moderate adherence to current PHD is inversely associated with diet-related GHGE and mortality risk. This underscores the importance of dietary shifts for improving public health and environmental sustainability.