Abstract
In 2019, the EAT-Lancet Commission proposed a healthy dietary pattern that, along with reductions in food waste and improved agricultural practices, could feed the increasing global population sustainably. We developed a Planetary Health Diet Index (PHDI) to quantify adherence to the EAT-Lancet reference diet. Objectives: We aimed to assess associations between PHDI and total and cause-specific mortality in 3 prospective cohorts of males and females in the United States. Methods: We followed 66,692 females from the Nurses’ Health Study (1986–2019), 92,438 females from the Nurses’ Health Study II (1989–2019), and 47,274 males from the Health Professionals Follow-up Study (1986–2018) who were free of cancer, diabetes, and major cardiovascular diseases at baseline. The PHDI was calculated every 4 y using a semiquantitative food frequency questionnaire. Hazard ratios (HRs) were calculated using multivariable proportional-hazards models. Results: During follow-up, we documented 31,330 deaths among females and 23,206 among males. When comparing the highest with the lowest quintile of PHDI, the pooled multivariable-adjusted HRs were 0.77 [95% confidence interval (CI): 0.75, 0.80] for all-cause mortality (P-trend < 0.0001). The PHDI was associated with lower risk of deaths from cardiovascular diseases (HR: 0.86; 95% CI: 0.81, 0.91), cancer (HR: 0.90; 95% CI: 0.85, 0.95), respiratory diseases (HR: 0.53; 95% CI: 0.48, 0.59), and neurodegenerative diseases (HR: 0.72; 95% CI: 0.67, 0.78). In females, but not males, the PHDI was also significantly associated with a lower risk of deaths from infectious diseases (HR: 0.62; 95% CI: 0.51, 0.76). PHDI scores were also associated inversely with greenhouse gas emissions and other environmental impacts. Conclusions: In 3 large United States-based prospective cohorts of males and females with up to 34 y of follow-up, a higher PHDI was associated with lower risk of total and cause-specific mortality and environment impacts.
Generated Summary
This research article presents a prospective cohort study designed to assess the association between the Planetary Health Diet Index (PHDI) and the risk of total and cause-specific mortality. The study utilized data from three large, United States-based prospective cohorts: the Nurses’ Health Study (NHS1), the Nurses’ Health Study II (NHS2), and the Health Professionals Follow-up Study (HPFS). The primary objective was to evaluate how closely adhering to the EAT-Lancet reference diet, as measured by the PHDI, correlated with mortality rates in these cohorts. The EAT-Lancet Commission proposed this diet, which emphasizes plant-based foods and limits animal-sourced foods, to promote both human health and environmental sustainability. The study followed participants over several years, assessing their dietary habits through food frequency questionnaires (FFQs) every four years. The researchers calculated the PHDI scores based on the participants’ adherence to the EAT-Lancet diet guidelines and used multivariable proportional-hazards models to assess the relationship between PHDI scores and mortality outcomes. The study aimed to determine if a higher PHDI score, indicating greater adherence to the sustainable diet, was associated with a reduced risk of mortality from various causes, including cardiovascular diseases, cancer, respiratory diseases, and neurodegenerative diseases.
Key Findings & Statistics
- The study included 66,692 females from NHS1, 92,438 females from NHS2, and 47,274 males from HPFS.
- During follow-up, the researchers documented 31,330 deaths among females and 23,206 deaths among males.
- When comparing the highest with the lowest quintile of PHDI, the pooled multivariable-adjusted hazard ratios (HRs) were 0.77 (95% CI: 0.75, 0.80) for all-cause mortality (P-trend < 0.0001).
- The PHDI was associated with lower risk of deaths from cardiovascular diseases (HR: 0.86; 95% CI: 0.81, 0.91), cancer (HR: 0.90; 95% CI: 0.85, 0.95), respiratory diseases (HR: 0.53; 95% CI: 0.48, 0.59), and neurodegenerative diseases (HR: 0.72; 95% CI: 0.67, 0.78).
- In females, the PHDI was also significantly associated with a lower risk of deaths from infectious diseases (HR: 0.62; 95% CI: 0.51, 0.76), but not in males.
- For a 20-point increase in the PHDI score, the HR for total mortality was 0.84 (95% CI: 0.82, 0.85).
- In the highest quintile of PHDI, the risk of cardiovascular mortality was reduced by 14% (HR: 0.86; 95% CI: 0.81, 0.91).
- The risk of cancer mortality was reduced by 10% (HR: 0.90; 95% CI: 0.85, 0.95).
- The risk of respiratory mortality was reduced by 47% (HR: 0.53; 95% CI: 0.48, 0.59).
- Neurodegenerative disease mortality was reduced by 28% (HR: 0.72; 95% CI: 0.67, 0.78).
- Infectious disease mortality risk reduction in females was 38% (HR: 0.62; 95% CI: 0.51, 0.76).
- The PHDI was inversely associated with total mortality in all subgroups.
- The association with total mortality was strongest among current smokers (HRQ5 vs. Q1: 0.72, 95% CI: 0.64, 0.82).
- Those consuming >10 g/d of alcohol (HRQ5 vs. Q1: 0.68, 95% CI: 0.64, 0.72) also had a lower risk.
- The inverse association with total mortality was significant in the Asian American group (HR: 0.70, 95% CI: 0.52, 0.94).
- In the environmental impact analysis, the highest PHDI quintile showed a 29% reduction in GHG emissions, a 21% reduction in fertilizer use, a 51% reduction in cropland use, and a 13% reduction in irrigation water needs, compared to the lowest quintile.
Other Important Findings
- The PHDI scores were calculated every 4 years using a semiquantitative food frequency questionnaire.
- The study used multivariable proportional-hazards models to calculate hazard ratios (HRs).
- The study found that a higher PHDI score was associated with lower risk of total and cause-specific mortality and environmental impacts.
- Higher PHDI scores were associated with greater consumption of whole grains, nuts, and unsaturated fats.
- Lower PHDI scores were associated with higher consumption of tubers, red/processed meats, eggs, added saturated fats, and added sugars.
- In all 3 cohorts, consumption of high-quality plant-based foods increased over time.
- Consumption of animal-based foods decreased over time.
- The increase of the total PHDI in NHS1 and NHS2 was attributable to increases in the scores for whole grains, unsaturated fats, saturated fats, nuts, poultry, red/processed meat, and tubers.
- PHDI had a moderate to strong positive correlation with AHEI, AMED, HEI-2015, and hPDI.
Limitations Noted in the Document
- The scoring of foods may not represent all major foods and their relationship with mortality in all countries.
- Measurement error of dietary intake is inevitable and will tend to bias true associations toward the null.
- Changes in diet due to the development of chronic disease could lead to over- or underestimation of the effect of adherence to the PHDI on mortality.
- Residual and unmeasured confounding cannot be completely controlled in this observational study.
- The restriction of participants to those with similar education and occupation limits confounding, which may limit the generalizability to the large population.
Conclusion
The findings of this study underscore the potential benefits of adopting a dietary pattern that aligns with the EAT-Lancet Commission’s recommendations for both human health and environmental sustainability. The research, conducted across three large, U.S.-based prospective cohorts, provides robust evidence that a higher PHDI score, indicating greater adherence to this diet, is significantly associated with reduced mortality risks. Specifically, the study revealed a substantial decrease in all-cause mortality and cause-specific mortality, including cardiovascular diseases, cancer, respiratory diseases, and neurodegenerative diseases. The study also highlights that specific food groups play critical roles in these associations. The inverse association with mortality was particularly evident with higher intakes of whole grains, nuts, and unsaturated fats. The environmental impact analysis further supports the benefits of this dietary approach, showing that a higher PHDI score is linked to lower greenhouse gas emissions and reduced demands on land and water resources. The study’s results align with previous research on planetary health diets and their positive impacts on health outcomes. The findings are particularly relevant given the global challenges of feeding a growing population sustainably while addressing the environmental impact of food production. The identification of key food groups that contribute to the inverse association with mortality provides valuable insights for dietary recommendations and interventions. The study’s comprehensive analysis, using data from multiple cohorts and accounting for various potential confounders, reinforces the robustness of the findings. The consistent results across different subgroups, including those with varying lifestyle factors, lend further credibility to the conclusions. The strengths of the study include the large sample size, the long-term follow-up with repeated dietary assessments, and the numerous sensitivity analyses. While acknowledging certain limitations, such as potential measurement errors and the restriction of participants to a specific demographic, the overall findings provide strong support for promoting diets that prioritize both human health and environmental sustainability. The study’s insights are especially timely given the urgent need for sustainable food systems and highlight the potential of dietary interventions to reduce the burden of chronic diseases while minimizing environmental impacts. These findings underscore the significance of the EAT-Lancet Commission’s recommendations and emphasize the potential for dietary changes to make a meaningful contribution to global health and environmental goals.