Associations of multiple dietary indices with health outcomes and diet-related greenhouse gas emissions in U.S. adults: Evidence from NHANES 2005–2018.

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Background: Dietary patterns directly influence both human health and environmental attributes, yet comparative evidence linking the duo-impacts of different dietary patterns to health outcomes and environment remains limited. Objectives: This study aimed to examine associations of multiple dietary indices with major chronic diseases (MCDs) (including cancer, diabetes, and cardiovascular diseases), all-cause mortality, and dietary-related greenhouse gas emissions (GHGE) among United States (US) adults. Methods: We analysed data from 27,517 US adults who participated in the National Health and Nutrition Examination Survey (NHANES) 2005–2018 and provided their disease information and two-day 24-hour diet recalls. Seven dietary patterns including the Healthy Eating Index-2020 (HEI-2020), Alternate Healthy Eating Index (AHEI), Dietary Approaches to Stop Hypertension (DASH), alternate Mediterranean Diet score (aMED), Planetary Health Diet Index (PHDI), American Cancer Society 2020 diet score (ACS2020), and the Dietary Index for Gut Microbiota (DI-GM) were assessed. Dietary-related greenhouse gas emissions were estimated by linking individual food intakes to dataFRIENDS, a food environmental impact database. All-cause mortality was obtained by linkage to the National Centre for Health Statistics mortality files up to 2019. Results: For MCDs, compared with those in the lowest quintile, participants in the highest quintile of HEI-2020, AHEI, DASH, aMED, and ACS2020 were significantly associated with 12-15% lower prevalence of MCDs. No significant associations were observed between seven dietary scores and cancer in this cross-sectional analysis. For all-cause mortality, all studied diet patterns showed strong inverse associations with risk of death, especially PHDI and DI-GM (about 48% lower risk of death in Q5 vs Q1). For environmental impact, higher dietary scores were associated with lower diet-related GHGE, especially ASC2020 and PHDI (1.84 and 1.31 kgCO2e/person/day lower in Q5 vs Q1, respectively). Conclusions: Overall, higher adherence to healthy dietary patterns was associated not only with better health outcomes but also lower diet-related GHG emissions, suggesting co-benefits for human health and environmental sustainability.