Plant-based dietary patterns are showing promising sustainability outcomes, reducing emissions, energy consumption, and land impact. However, they also come with trade-offs like increased water usage and higher costs, highlighting the intricate balance in achieving diet sustainability.
A study published in The American Journal of Clinical Nutrition has delved into the associations between eight commonly used diet quality indexes (DQIs) and seven sustainability indicators within a nationally representative U.S. sample. This research fills a crucial gap in understanding how dietary patterns influence sustainability and can inform potential policy actions.
The connection between diet and health is fundamental in shaping medical practice guidelines and public health policies. Diet quality indexes (DQIs) allow for the quantitative expression of diet quality, enabling comparisons between different diets. Newer DQIs have started incorporating sustainability as one of their criteria, alongside scoring for nutrient content, food proportions, and specific food groups.
Food production and consumption have a significant environmental footprint, contributing to 35% of global greenhouse gas emissions (GHGE), 40% of land use, and 70% of freshwater consumption. In the US, the diet is responsible for 20 – 25% of these environmental metrics. The US, which has the highest food-related GHGE globally, 70% above the global average, adopted the National Strategy on Hunger, Nutrition, and Health in 2022. This strategy aims to promote accessible, sustainable, and healthy diets and emphasizes research on the link between healthy eating and sustainability. Given that dietary patterns vary in their environmental impacts, a comprehensive evaluation of dietary quality indices using diverse sustainability indicators is essential.
The present study utilized eight different indices, namely the Healthy Eating Index-2020 (HEI-2020), Alternate Healthy Eating Index-2010 (aHEI-2010), Mediterranean Diet Score (Med), Alternate Mediterranean Diet Score (aMed), Healthful Plant-Based Diet Index (hPDI), Planetary Health Diet Index (PHDI) for the United States, Dietary Approaches to Stop Hypertension Index (DASH), and Nutrient-Rich Foods Index 9.3 (NRF9.3).
These indices follow different guidelines. For instance, the HEI-2020 adheres to the Dietary Guidelines for Americans (DGA), the Med and aMed are based on the Mediterranean diet modified for Americans, the hPDI focuses on a plant-based nutritious diet, the PHDI aligns with sustainability recommendations, and the DASH diet is designed to control blood pressure. The NRF9.3 is centered around 12 nutrients with set daily values.
Diet cost was also examined, using the Purchase-to-Plate Price Tool (PPPT) along with derived prices for food eaten outside the home, as this accounts for over half of food spending in the US.
Data on dietary habits was sourced from the National Health and Nutrition Examination Survey (2011–2018) and analyzed in the context of sustainability indicators obtained from public domain databases. These sustainability indicators included greenhouse gas emissions (GHGE), water scarcity footprint (WSF), cumulative energy demand (CED), land, fertilizer nutrients, pesticides, and food prices.
The analysis demonstrated that, consistent with previous studies, higher diet quality was associated with lower daily GHGE per capita and reduced land use. A healthier diet was also linked to lower CED in five out of the eight diets (with the exceptions being HEI-2020, Med, and aMed).
Fertilizer use was lower for healthy diets, except in the cases of NRF9.3 and DASH. However, healthier diets required greater water utilization, as indicated by a higher WSF, and were more costly.
Healthy eating tended to involve more seafood, plant-based foods, fats, and oils, while including less red meat, refined grains, beverages, and sweeteners. The former group was associated with a higher environmental impact in some aspects, while the opposite was true for the latter.
Dairy, egg, and poultry consumption did not show a consistent trend with either the DQIs or sustainability. Pesticide use had conflicting associations with the DQI.
The aHEI-2010 and hPDI were associated with the highest number of positive sustainability outcomes and the fewest negative ones, with five and two respectively. The PHDI had a 4:1 ratio of positive to negative outcomes, while Med and aMed both had a 4:2 ratio.
The least sustainable diets were HEI-2020 and DASH (each with a 3:2 ratio), and NRF9.3 (with a 3:4 ratio). The commonly used HEI-2020, which is based on the DGA, uses more water and is more costly but has lower GHGE, land use, and fertilizer use, as expected from prior research.
Plant-based diets had the strongest associations with sustainability parameters compared to nutrient-based or animal-based foods. This was reflected in the best quality-sustainability balance for aHEI-2020 and hPDI.
Nutrient-based diets and the DASH diet were less sustainable than food-based diets or those incorporating both foods and nutrients. The former were also linked to greater fertilizer and pesticide use.
The paper thus suggests that expanding diets recommended or used in specific countries globally may have mixed environmental effects.
Healthier diets have long been considered and promoted as more sustainable by dietary experts. This current study is the first to directly compare 56 DQI-sustainability parameter pairings.
The findings reveal a more complex picture, indicating trade-offs between diet quality and sustainability regardless of specific dietary patterns. Nevertheless, some trends do emerge, such as GHGE, CED, land, and fertilizer use generally being lower for healthier diets. Additionally, plant-based diets appear to be more sustainable.
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