Healthy diets can create environmental trade-offs, depending on how diet quality is measured

Conrad Z, Blackstone NT, Roy ED. Healthy diets can create environmental trade-offs, depending on how diet quality is measured. Nutrition Journal. 2020 2020/10/27;19(1):117. 

Relevant to: 

All Dietitians-Nutritionists.  

 Question: 

This study integrates nutritional epidemiology and food system science methods to evaluate the relationship between diet quality and environmental sustainability, while also taking food loss and waste into account. This study is unique to previous studies in that it assesses individual, self-selected diet patterns (I.e., what people actually eat), instead of theoretical diets that follow specific dietary recommendations (e.g., national guidelines or vegetarian diets). Further, it examines environmental impacts beyond climate change.   

Bottom line for nutrition practice: 

Data was assessed for quality using both the Healthy Eating Index (HEI) and Alternative Healthy Eating Index (AHEI) (see of additional interest for more details). Higher diet quality was associated with higher Total Food Demand, retail loss, inedible portions, consumer waste, and consumed food. Higher diet quality was also linked to lower use of agricultural land. The results also show, however, that the relationship between diet quality and agricultural resource use beyond land (fertilizer nutrients, pesticides and irrigation water) is dependent on which tool is used to measure diet quality.  

The authors assert that the association between diet quality and environmental sustainability is more nuanced than formerly recognized. They note that healthy diets are not necessarily more environmentally sustainable, but that they can be under certain circumstances. They suggest that dietary guidelines may need to be balanced with considerations of environmental sustainability beyond the frequent measures of land use and greenhouse gas emissions. Additionally, as diet quality was shown to increase food loss and waste, policies and guidelines need to avoid trade-offs between these two goals.  

Finally, the authors stress the need for standardized metrics for measurement (e.g., diet quality, impact on environment, food loss and waste), and suggest that assessment should focus on environmental impacts of individual, self-selected diet patterns, not on individual foods.  

Abstract:

Background: There is an urgent need to assess the linkages between diet patterns and environmental sustainability in order to meet global targets for reducing premature mortality and improving sustainable management of natural resources. This study fills an important research gap by evaluating the relationship between incremental differences in diet quality and multiple environmental burdens, while also accounting for the separate contributions of retail losses, inedible portions, and consumer waste.  

Methods: Cross sectional, nationally-representative data on food intake in the United States were acquired from the National Health and Nutrition Examination Survey (2005–2016), and were linked with nationally-representative data on food loss and waste from published literature. Survey-weighted procedures estimated daily per capita food retail loss, food waste, inedible portions, and consumed food, and were summed to represent Total Food Demand. Diet quality was measured using the Healthy Eating Index-2015 and the Alternative Healthy Eating Index-2010. Data on food intake, loss, and waste were inputted into the US Foodprint Model to estimate the amount of agricultural land, fertilizer nutrients, pesticides, and irrigation water used to produce food.  

Results: This study included dietary data from 50,014 individuals aged ≥2 y. Higher diet quality (HEI-2015 and AHEI- 2010) was associated with greater per capita Total Food Demand, as well as greater retail loss, inedible portions, consumer waste, and consumed food (P < 0.001 for all comparisons). Consumed food accounted for 56–74% of agricultural resource use (land, fertilizer nutrients, pesticides, and irrigation water), retail loss accounted for 4–6%, inedible portions accounted for 2–15%, and consumer waste accounted for 20–23%. Higher diet quality was associated with lower use of agricultural land, but the relationship to other agricultural resources was dependent on the tool used to measure diet quality (HEI-2015 vs. AHEI-2010).  

Conclusions: Over one-quarter of the agricultural inputs used to produce Total Food Demand were attributable to edible food that was not consumed. Importantly, this study also demonstrates that the relationship between diet quality and environmental sustainability depends on how diet quality is measured. These findings have implications for the development of sustainable dietary guidelines, which requires balancing population-level nutritional needs with the environmental impacts of food choices.  

Details of results: 

Higher diet quality using the AHEI is associated with similar or decreased use of all agricultural resources (agricultural land, fertilizer nutrients, pesticides and irrigation water). When using the HEI, however, higher diet quality is linked to lower land use, no difference in use of fertilizer nutrients, but increased use of pesticides and irrigation water. As noted above, The Healthy Eating Index (HEI) was designed to evaluate compliance with the 2015–2020 Dietary Guidelines for Americans, thus it is reflective of the Dietary Guidelines. The Alternative Healthy Eating Index (AHEI), on the other hand, was created based on foods and nutrients associated with reducing the risk of chronic disease. 

The authors pose that these results can be partly explained by the following: i) fruits, vegetables, and nuts (typical components of a healthy diet pattern), usually require substantially greater inputs per unit land area than most other foods; ii) sugar-sweetened beverages and refined grains have relatively limited environmental impacts; and iii) consumption of red and processed meat (linked to negative health and environmental impacts) is not reflected in the HEI, whereas it is indicated in the AHEI.  

Higher diet quality (measured by both HEI and AHEI) was associated with higher Total Food Demand and increased food loss and waste. These results suggest that there are trade-offs between the goals of improved nutrition and decreased waste; policies need to consider how to mitigate the effects of food loss and waste while promoting nutrition. Over one-quarter of the agricultural inputs used to generate Total Food Demand were attributable to edible food that was not consumed. For each agricultural resource category, consumed food accounted for 57–74%, retail loss 4–5%, inedible portions 2–15%, and consumer waste 20–23%.  

As human diets are significant contributors to ecological crises, the authors urge that the creation of sustainable dietary guidelines – although requiring complex institutional processes, political will, and interdisciplinary knowledge – should be a priority.  

The authors note that a limitation occurred due to their use of their modelling of a closed food system (in the US), where all was produced domestically. Further, the model does not estimate water scarcity.  

 Of additional interest: 

The Healthy Eating Index (HEI) was designed to evaluate compliance with the 2015–2020 Dietary Guidelines for Americans, whereas the Alternative Healthy Eating Index (AHEI) was created based on foods and nutrients associated with reducing the risk of chronic disease. The authors provide further explanation of how the HEI and AHEI were derived within the discussion.  

Editor’s comment:  

Similar to what is seen across the globe, consumer waste accounted for 20–23% of agricultural inputs.  
It would seem that decreasing food waste should be a fundamental aspect of sustainable dietary guidelines.  

It’s great to see a study that includes fertilizer and pesticide use; it would also be helpful to see further research linking these types of results to studies illustrating the environmental impact of fertilizer and pesticide use.  

Open access link to article: 

https://nutritionj.biomedcentral.com/articles/10.1186/s12937-020-00629-6 

Conflict of interest/ Funding: 

N/A (no competing interests) 

External relevant links:  

N/A

Corresponding author: 

Zach Conrad: zsconrad@wm.edu 

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