Adherence to a planetary health diet, diet-related greenhouse gas emissions, functional disability, and mortality in older adults

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.

This prospective study included 8043 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 four categories: ≤25 (n = 1061; very low), 26–27 (n = 1703; low), 28–30 (n = 3368; moderate), and ≥31 (n = 1911; high) points. Diet-related GHGEs were calculated using previously developed GHGE tables for each food item.

During the median 4.75-year follow-up period, 659 deaths and 1431 incidents of functional disability were recorded. After adjusting for confounders, the hazard ratios (HRs) of mortality were lower in the moderate-adherence group than in the very low-adherence group (HR, 0.64; 95% confidence interval, 0.60–0.93). PHD scores tended to be inversely associated with functional disability (p for trend = 0.081). However, diet-related GHGEs were not associated with mortality or disability. The PHD score ranges with the lowest HRs for mortality and mean diet-related GHGE were 28–30 and 29–31 points, respectively.

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.