Improving diets is one of the world's biggest public health and environmental challenges. More than 2.5 billion adults are now overweight or obese, 88% of countries with available data face a serious burden of two or more forms of malnutrition, and food systems account for between a quarter and a third of global greenhouse gas emissions.

Published in Nature Food, the study introduces MATILDA (Micro-Macro Assessment Tool to Identify Low-impact Dietary Actions), a global database that combines individual dietary surveys with country-level food supply chains and population data. Covering 165 countries, it provides a globally harmonized picture of how the nutritional quality and environmental impacts of diets vary within populations, offering policymakers a stronger evidence base than national averages alone.

Looking beyond national averages revealed how widely diets differ within countries. The highest-impact diets produced almost double the greenhouse gas emissions of the lowest-impact diets. 

Across the 165 countries studied, every 5% improvement in diet quality, measured using the Alternative Healthy Eating Index (AHEI), was associated with a 7.7% reduction in diet-related greenhouse gas emissions, alongside lower water and land use. Diets containing a higher proportion of plant-based foods were also consistently associated with lower environmental impacts. 

People's dietary patterns are shaped by far more than personal choice. Where they live, whether that is a town or the countryside, how long they spent in education, what they can afford and the wider social and environmental context all play a part. Recognising those differences creates opportunities to develop food policies that better reflect the realities in which people make food choices.

Dr Oliver Taherzadeh, lead author from the Institute of Environmental Sciences (CML), Leiden University, said:

"MATILDA connects what's on our plate to global environmental consequences. We achieve this by linking group-level dietary patterns to a macroeconomic model which captures their impact within and beyond national borders. To date, macroeconomic food system models have overlooked national-level differences in food consumption patterns and integration of food supply chain data into country case studies has been piecemeal. We try to bridge this gap and in doing so manage to pin-point the high-impact and vulnerable consumer groups otherwise hidden by dietary food modelling and policy. This enables sustainable dietary policy to be more targeted, fair and effective."

Dr Hongyi Cai, developer of MATILDA from the Institute of Environmental Sciences (CML), Leiden University, said:

*"There is no one-size-fits all when it comes to sustainable and healthy diets. When we benchmark the population against the actual diets they follow, food system impacts become more accountable, health inequalities become more explicit, and differentiated needs become more clear." *

Professor Paul Behrens, co-author at the Oxford Martin School, University of Oxford, said:

"People don't make food choices in isolation. What we eat is shaped by where we live, what we can afford and what is available to us. We've entered an era where food policy can become much more evidence-based. Instead of treating entire populations as though they eat the same foods, we can now identify where interventions are likely to have the greatest benefit while making sure vulnerable groups aren't left behind."

The paper discusses a range of possible policy responses, including public information campaigns, supermarket incentives and other measures that make healthier, lower-impact choices easier. Broader approaches, such as taxation and regulation, also have an important role. The authors conclude that uniform interventions are unlikely to be sufficient, because dietary patterns and nutritional needs differ within populations.

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