Protein labels beat carbon labels in meat-reduction nudge trials, Cambridge study found

A new peer-reviewed study led by University of Cambridge researcher Chris Macdonald found that highlighting protein content significantly increased consumer selection of meat-free options, outperforming carbon footprint labels in controlled choice experiments and pointing to 'protein' as a key perceived barrier to reducing meat consumption.

• A survey of 1,500 UK students identified 'protein' as the most frequently cited barrier to adopting a meat-free diet.

• Two choice experiments (total N=3,000) found protein-content labeling significantly increased selection of meat-free options versus control and carbon labels.

• The study proposed 'nudge by proxy' interventions that targeted internal motivations and warned against 'insufficiency' and 'availability' illusions in meat-free options.

Published in Frontiers in Sustainable Food Systems, the research set out to explain why widely tested interventions such as carbon labeling often delivered modest, inconsistent behavior change, and to trial an alternative approach grounded in consumer motivations rather than environmental messaging.

Macdonald argued that sustainability labels could suffer from an 'environmentalist bias', where interventions reflected what motivated researchers more than what persuaded everyday consumers. To counter that, the study began with a consumer-centric survey designed to identify the most commonly stated reason people resisted switching away from meat.

Using open-text responses from 1,500 UK-based students aged 18-25 who were neither vegetarian nor vegan, the survey found protein was the most frequent term across question formats and genders, appearing far more often than other commonly cited factors such as taste or cost. The findings suggested that for this demographic, concerns about meeting protein needs acted as a psychological barrier to meat-free choices, even when suitable alternatives existed.

The study then tested whether addressing that concern directly, without emphasizing environmental impacts, could shift choices in a measurable way. In the first experiment, participants selected between a meat sausage roll and a vegan alternative in a menu-style setting. Protein labeling significantly increased selection of the meat-free option compared with both a control label and a carbon-footprint label, while carbon labeling did not produce a statistically significant change versus control.

A second experiment tested a similar approach using a different product choice, again finding that protein labeling more than doubled selection of a meat-free option compared with control. Adding fat information alongside protein, described as a 'polynudge', did not further improve results versus protein alone.

Macdonald described the approach as a 'nudge by proxy', aimed at reducing an external cost, such as emissions, by targeting internal motivations that consumers already prioritized. The paper also introduced two risks for future intervention design: an 'insufficiency illusion', where consumers wrongly assumed meat-free options lacked key benefits such as protein, and an “availability illusion,” where meat-free options existed but were genuinely inferior in areas consumers valued.

While the results were consistent across experiments, the author noted limitations, including the narrow demographic focus and the hypothetical online settings, and called for replication in real-world purchase environments and across broader consumer groups. The paper also argued that better labeling alone was not sufficient if the products being promoted did not meet expectations around taste, nutrition, convenience, and value.