Eating for Net Zero: the role diets can play in the transition to lower environmental impact

Sustainable diets project for WWF-UK

A large portion of the global greenhouse gas emissions are associated with the food system and urgent action is needed to prevent us and future generations from environmental disasters, such as global warming and loss of nature. At the same time food and nutrition need to be secured for the growing world population. Adopting a healthy and sustainable diet is needed to achieve this. In response to the Paris Climate Agreement, WWF-UK updated the Livewell Plates, and brought the sustainable diets debate to the attention of the public. With this publication WWF-UK showed that changing our diet can make a major contribution to reducing the environmental impact of our food system. At that time, Blonk supported WWF-UK to realize this update and show that by adopting a sustainable diet it is possible to limit global warming to less than 2 degrees. Following the approach of the 2016 study WWF-UK commissioned Blonk in 2021-2022 again to model the Livewell diet and investigate how diet shift can enable a nature positive net-zero transition in the UK.

In this research project we used our optimization software Optimeal and compared the Livewell diet to the current average diet of the UK population. With the help of the optimization software we could find a unique combination of foods that meet certain requirements constraints, such as environmental impact, nutritional requirements, while staying as close to the current diet as possible. The study confirms, what also other studies have shown, that what people eat can play a positive role in reducing consumer impacts. The findings show that dietary change is an essential ingredient in achieving net zero emissions in the food system. While climate action on agriculture and land use can mitigate emissions and free up land for nature-positive effects.

Methodology: Calculating a sustainable diet

We conducted this study using Optimeal, a software tool to optimize dietary patterns taking into consideration both sustainability and health for different population groups, such as children (different age groups), adolescents, adults and elderly, while keeping closest to the current diet as possible. 

1. Reference diet (current diet)
   

   The starting point for the optimization is a reference diet. In this case the current UK diet, based on the most recent National Diet and Nutrition Survey data. To derive nutritional composition data, dietary intake data was linked to the UK Nutrient Databank, which includes product composition data on a larger range of processed foods and composite dishes compared to the UK food composition tables. Efforts were also made to expand the UK Nutrient Databank, creating additional categories, and assigning food products to disaggregated categories where necessary. The detailed and extensive dietary data were aggregated, and the final dataset covered 393 food products across all age groups.

2. Environmental impact of food products
   

   To determine the environmental impact of food products, we used Life Cycle Assessment (LCA) methodological framework, according to the ISO 14040 and 14044 guidelines. For 244 food products, as well as whole foods as processed foods, LCAs were performed, based on the Optimeal EU dataset. Background processes were adjusted to the specific UK situation, such as electricity, and import and export data. Furthermore, the functional unit was mass based (100 gram of food product) and economic allocation was used. By using proxies, we could include the environmental impact of the 393 food products.

3. Constraints
   

   In order to optimize certain boundaries (or constraints) are needed. In this study constraints related to nutrition, environment, costs, and acceptability were included.
   • Nutritional constraints were linked to dietary reference values, based on recommendations from the Scientific Committee of Nutrition and its predecessor, the Committee on Medical Aspects of Foods and were obtained from a compilation published by Public Health England. Eatwell Guide recommendations were used to establish nutritional constraints for certain food groups.
   • For environmental constraints various environmental impact categories were included, such as GHG emissions, water use, acidification, and biodiversity loss.
   • The cost of the food items was estimated to calculate the price of each diet. This was done by collecting price information in several UK online supermarkets, using automated data collection techniques.
   • To create acceptable outcomes, the dietary solutions were kept close to the current diet by limiting dietary changes to 33-150% of the current amount of each food group.

We applied a stepwise Greenhouse Gas (GHG) emissions reduction while also ensuring that the diets met nutritional requirements and that they did not increase in other environmental impact or prices, and identified the diet that was best balanced with culturally acceptability.

Results and findings

The findings show that with a dietary change it is possible not to exceed the planetary boundary for GHG emission, whilst meeting the nutritional needs, being cultural acceptable and without increasing the price of the diet

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