Subtle behavioral nudges aimed at diners can significantly reduce restaurant food waste, even in countries where packaging leftovers for future consumption is attached to financial-centered shame or other social stigmas, new research suggests.

In an article published April 2 in European Economic Review, researchers conducted a field experiment involving 14 restaurants and 23,612 customers in Turin, Italy, to see how behavioral interventions could reduce or eliminate restaurant leftovers. 

"Social motivation is dominant in dictating consumer behavior in restaurants (and, indeed, it is also the main result we find)," Marianna Gilli, co-author of the study and a researcher at the Università degli Studi di Ferrara, told The Academic Times. "Culturally, in our country [Italy], going to a restaurant and taking home leftovers of uneaten food is considered either a sign of financial distress or stinginess, both of which may trigger feelings of shame."

According to a 2021 United Nations report, 26% of the world's estimated 931 million tons of food waste is generated by the service sector, and one of the largest components of food waste in the service sector is consumers' plated leftovers. Previous studies have found that providing customers with "doggie bags" in which to carry home leftover food is effective at reducing food waste in restaurants, but in some countries, shame and social stigma, driven by fears of appearing financially insecure, greedy or ill-mannered, make diners more reluctant to package and take home leftover food.

Gilli does not believe restaurants have contributed directly to this social stigma in the context of this particular study, but she explained that, until recently, restaurants in Italy were not sufficiently equipped to satisfy an increased demand for doggie bags, and limited supply might have slowed the spread of better consumer habits pertaining to leftover food.

Building on previous literature suggesting that the activation of social norms can stimulate pro-social behaviors, Gilli and her colleagues applied two different nudges to diners: manipulating the descriptive social norm and automatically delivering doggie bags to tables.

The first intervention, manipulation of the descriptive social norm, sought to reduce stigma by informing customers that social norms pertaining to doggie-bag usage are changing. This nudge had a significant positive impact on diners, doubling the number of doggie bags accepted and used. 

In the second intervention, waiters were instructed to automatically deliver doggie bags to diners as a default option. This nudge did not have a significant impact on doggie-bag usage, although it apparently encouraged customers to eat more from their plate prior to their departure. 

A third group of restaurants, in which neither intervention was applied, was used as a control.

Gilli said the default nudge's poor performance overall compared with the social-norm intervention's observed success came as a surprise to the research team, because prior literature indicated that default options generally exerted a significant effect on outcomes. In fact, Gilli's initial assumption was that consumer laziness would render the preemptive provision of doggie bags even more appealing, since no action or effort was required on behalf of the consumer to change outcomes.

Instead, the findings suggest that the default nudge implicitly discouraged leaving food on one's plate, communicating that customers should eat more up front, despite the availability of doggie bags. The social-norm nudge model, on the other hand, pointed to an increase of 0.65 doggie bags per day in each treated restaurant. Compared to the average number of doggie bags used prior to the treatment period, this amounts to an increase of approximately 100%.

At the individual level, social-norm modification resulted in an increase between 1.4% and 1.7% in the probability of a customer taking a doggie bag compared with pre-intervention trends.

"While changing the prevailing social norm allows the client to know that taking the doggie bag is socially acceptable, the default option — which implies that the doggie bag is given to you unless you communicate differently — is not giving any information on the acceptability of the behavior, so it does not 'ease' any sense of shame that may arise," Gilli told The Academic Times.

In very crowded restaurants, however, the default option did have a statistically significant impact, with an approximately 0.01 percentage-point increase in the probability a customer would accept and use a doggie bag. This outcome supports the notion that shame might be diminished in busier restaurants, since individual behavior is not as visible to other customers, and the concealment of doggie bags is slightly easier. 

However, the solution to fighting the stigma surrounding food waste more generally goes beyond the actions of individual customers or restaurants, Gilli said.

"A necessary policy keyword should be 'education' — that is, to educate consumers to make more conscious choices about food and to be more aware of the quantity of waste that is created by food consumption," Gilli said. "Promoting a greater focus on health and the body's needs when it comes to sitting down to eat [could] help reduce the amount of food that is ordered so that there are fewer leftovers."

Some diners may cite environmental concerns over the extra packaging used for restaurant leftovers, but Gilli said awareness of the bigger picture remains key. 

"In general, it can be said that it is a matter of choosing between two problems: on the one hand, throwing away food, and on the other hand, increasing the waste of materials such as plastic and aluminum," Gilli said. "From a purely environmental point of view, both choices are waste generation. The consumer's personal motivation and awareness are therefore crucial."

The article, "Nudging food waste decisions at restaurants," published April 2 in European Economic Review, was authored by Matilde Giaccherini and Mariangela Zoli, Sustainability, Environmental Economics, and Dynamic Studies (SEEDS) and Università degli Studi di Roma Tor Vergata; Marianna Gilli and Susanna Mancinelli, SEEDS and Università degli Studi di Ferrara.