People find it notoriously difficult to change eating habits to improve their own health, let alone the planet’s.

Now European researchers who explored factors that might motivate shifts to more sustainable diets are suggesting that social norms and self-efficacy are the most important.

The work by Sibel Eker and Michael Obersteiner, from the International Institute for Applied Systems Analysis in Austria, and Gerhard Reese, from Germany’s University of Koblenz-Landau, supports evidence that peer group values are more powerful than scientific facts in shaping people’s beliefs and actions about climate change.

Their findings are presented in a paper in the journal Nature Sustainability.

The study was motivated by increasing calls for people to adopt plant-based diets as part of radical shifts needed to address the destructive impact of current farming practices on the environment.

A key target is red meat, which vastly exceeds other food sources in terms of its land use, irrigation and greenhouse gas emissions, and is unsustainable in the face of population growth and climate change.

Red meat also has been associated with chronic health conditions, including diabetes, heart disease and some cancers.

On this front alone, calculations suggest that if, on average, the world adopted a flexitarian diet (one portion of red meat per week), it could potentially prevent more than 10 million deaths each year.

Eker wondered if such “ambitious scenarios” were attainable.

“I was observing my social network and society,” she says, “like more and more people being meat-reducers, new vegetarian restaurants in urban areas, and it made me curious about where these dynamics could lead.”

Although many people are reducing their meat intake in several countries, widespread resistance means that global levels needed to translate into environmental gains are still beyond reach. 

To explore how pervasive behavioural changes in meat consumption might be achieved, Eker and colleagues used an integrated assessment model to simulate population dynamics.

Based on prominent psychological theories on environmental action, combined with models from management science, it includes income, social norms, climate risk perception, health risk perception, self-efficacy and response efficacy (belief that one’s actions can make a difference), as well as age, gender and education level.

They simulated the model 10,000 times to find the optimal outcome.

“This was an exploratory modelling study,” explains Eker, “meaning that we used the model as a platform to experiment with different scenarios to find the most important drivers of diet shifts.”

Although she expected concern about health risks to be more important, Eker was not surprised that social norms – unwritten rules of behaviour considered acceptable in a group or society – were a leading motivator of diet change, because they create a strong, positive feedback loop, she says.

Put differently, “As there are more vegetarians around, visibility of the phenomenon increases, therefore adoption increases”.

The other key driver was self-efficacy, particularly in females, referring to perceived control over one’s behaviour and ability to change.

Results showed that this model would yield the most rapid behaviour changes for people aged 15 to 44 years, even when their adoption of vegetarian diets is low.

But even if 40% of the population became vegetarian, the model predicted that the environmental benefits may not be fully realised if everyone else continues their current meat consumption, suggesting that change requires a population-wide shift in eating patterns.

The researchers conclude that their findings demonstrate the importance of factoring human behaviour into climate change mitigation efforts and suggest that future research also account for variations in cultural attitudes and world views.

“We can use models to explore the social and behavioural aspects of climate change and sustainability problems in the same way as we explore the economic and environmental dimensions of our world,” says Eker.

This could provide a better understanding of how to motivate the lifestyle changes that are essential to address the predicaments facing the planet.