Health and environmental impacts of plant-rich dietary patterns: a US prospective cohort study

BACKGROUND: Diets that are rich in animal-based foods threaten planetary and human health, but plant-rich diets have varied health and environmental effects. We aimed to characterise a healthy dietary index and three plant-based indices by their environmental impacts and associations with risk of cardiovascular disease. METHODS: In this prospective cohort study, we used data from a food-frequency questionnaire in the US-based Nurses’ Health Study II. Participants were categorised by quintiles of four dietary indices, including the alternative healthy eating index-2010 (AHEI), plant-based diet index (PDI), unhealthy PDI, and healthy PDI. We calculated environmental impacts (greenhouse gas emissions and irrigation water, nitrogenous fertiliser, and high-quality cropland needs), and relative risks (RRs) of cardiovascular disease from 1991–2017, comparing quintiles. FINDINGS: We included 90 884 participants in the health-impact analysis and 65 625 participants in the environmental-impact analysis. Comparing the top and bottom quintiles, higher AHEI scores were associated with a decreased cardiovascular disease risk (relative risk 0·77 [95% CI 0·66–0·89]); 30% lower greenhouse gas emissions (Q5 2·6 kg CO(2) equivalent vs Q1 3·7 kg CO(2) equivalent); and lower fertiliser, cropland, and water needs (all p(trends)<0·0001). Similarly, the highest healthy PDI and PDI quintiles were associated with a decreased cardiovascular disease risk (healthy PDI 0·71 [0·60–0·83] and PDI 0·74 [0·63–0·85]) and lower environmental impacts (PDI water needs p(trend)=0·0014; all other p(trends)<0·0001). Conversely, the highest unhealthy PDI quintile had a higher cardiovascular disease risk compared with the lowest unhealthy PDI quintile (1·15 [1·00–1·33]; p(trend)=0·023) and required more cropland (p(trend)<0·0001) and fertiliser (p(trend)=0·0008). INTERPRETATION: Dietary patterns that are associated with better health had lower greenhouse gas emissions and nitrogenous fertiliser, cropland, and irrigation water needs. Not all plant-based diets conferred the same health and environmental benefits. US dietary guidelines should include nuanced consideration of environmental sustainability. FUNDING: US National Institutes of Health.