A groundbreaking new study published in Frontiers in Sustainable Food Systems has revealed a strikingly effective strategy for increasing the consumption of low-emission foods, potentially reshaping how sustainability is approached in consumer behaviour research. The study was led by Dr Chris Macdonald, a Cambridge scientist and Director of the Better Protein Institute, whose “nudge by proxy” method focuses on appealing to people’s personal motivations rather than their environmental conscience. In a series of large-scale experiments involving 3,000 participants, this approach more than doubled the selection of meat-free meals, proving significantly more successful than the traditional carbon footprint labelling techniques often used to promote sustainable food choices. The results suggest that behavioural change in favour of sustainability may be more easily achieved when interventions are designed from the consumer’s perspective rather than that of environmental advocates.

At the heart of Dr Macdonald’s research lies a crucial psychological insight: the “false consensus effect”, which leads individuals to overestimate the extent to which others share their values and beliefs. He argues that this effect can cause researchers, particularly those with strong environmental convictions, to design interventions that mirror their own motivations rather than those of the general public. “Researchers who are environmentalists may assume that emphasising climate impacts will sway others in the same way it persuades them,” Dr Macdonald explains. “I call this the environmentalist bias.” To counter this, he adopts a participatory approach that involves engaging directly with consumers before creating new behavioural interventions, ensuring that his designs are aligned with what genuinely influences their choices.

The study began with an extensive survey of 1,500 consumers, which identified a consistent concern among respondents: that meat-free diets might lack sufficient protein. Dr Macdonald terms this widespread misconception the “insufficiency illusion”—a false belief that plant-based meals are nutritionally inferior. Drawing on this insight, his team developed a simple yet powerful intervention: a label that highlighted the protein content of meat-free foods, rather than their environmental benefits. This slight but strategic shift reframed the narrative around plant-based options, emphasising their nutritional strengths. One of the most striking examples came from Greggs’ Vegan Sausage Roll, which, contrary to popular perception, not only produces fewer greenhouse gas emissions and contains less fat than the traditional sausage roll, but also offers more protein. The same holds for Greggs’ breakfast roll range, reinforcing the notion that meat-free alternatives can be both nutritious and satisfying.

The experiments revealed that such a seemingly minor adjustment in messaging could produce extraordinary results. “By simply highlighting the protein content, we were able to shift an unprecedented number of consumers towards meat-free choices,” says Dr Macdonald. In the control group, less than a quarter of participants chose the meat-free option, while in the group exposed to the protein label, over half did so—an increase of more than 100 per cent. The finding held steady across genders and age groups, making it one of the most consistent effects observed in sustainable food research to date. This dramatic behavioural shift transformed the meat-free choice from a minority preference into the majority decision, marking what Dr Macdonald describes as a “step-change” in the effectiveness of interventions aimed at reducing dietary emissions.

Following the success of his experiments, Dr Macdonald took the unusual step of directly sharing his findings with Greggs, the UK’s leading bakery chain and the company behind the famed Vegan Sausage Roll. He published an open letter on social media. He sent detailed communications to key Greggs executives, including CEO Roisin Currie, Head of Sustainability Paul Irwin-Rhodes, Customer & Marketing Director Hannah Squirrell, Product Development & Innovation Lead Sarah Graham, Brand Communications & Creative Lead Fiona Mills, and Head of Brand and Communications Ian White. His message to them was clear: Greggs now has a data-backed opportunity not only to boost sales but to enhance its reputation as a sustainability leader. “At the Better Protein Institute, we are committed to turning research into tangible impact,” Dr Macdonald explained. “That is why I have shared the results with Greggs and offered to collaborate with them—they have my contact information. The ball is in their court now.”

In reflecting on the broader implications of his work, Dr Macdonald challenges what he sees as a defeatist narrative surrounding sustainable consumption. “A rising tide of global meat consumption fuels a dangerous idea—that changing eating habits is too difficult,” he warns. “My work provides a defiant counter-narrative. With a data-driven approach, I continue to uncover new interventions that outperform traditional strategies.” His philosophy, which he describes as “data-driven, defiant optimism in action,” rests on a belief that real progress comes from understanding human psychology, engaging meaningfully with consumers, and resisting the pessimism that often clouds environmental discourse. If widely adopted, his “nudge by proxy” method could redefine how businesses and policymakers encourage sustainable choices—showing that the path to a greener future may begin not with moral pressure, but with empathy, insight, and a clear understanding of what truly motivates people.

More information: Chris Macdonald, Reducing meat consumption with consumer insights and the nudge by proxy: the anomaly of asking, the power of protein, and illusions of insufficiency and availability, Frontiers in Sustainable Food Systems. DOI: 10.3389/fsufs.2025.1656336

Journal information: Frontiers in Sustainable Food Systems Provided by Lucy Cavendish College, University of Cambridge