Food waste is a major contributor to climate change; food accounts for 20% of global greenhouse gas emissions (Hertwich and Peters, 2009), and 92% of the global water footprint is related to agriculture (UNEP, 2012). Globally, about one-third of all food is lost or wasted (Gustavsson et al., 2011), yet food waste has long been neglected as an environmental problem.

Two interventions designed to influence food consumption norms through external cues were tested in a chain of hotels:

• The size of plates used for hotel breakfast buffets, and in some cases also lunch and dinner buffets, was reduced from 24 to 21 cm.
• A sign displayed at the buffet provided a direct social cue by encouraging restaurant guests to help themselves more than once. The text read, in seven languages: “Welcome back! Again! And again! Visit our buffet many times. That’s better than taking a lot once.”

Recruited hotels either implemented the interventions over 1.5 months or served as the control group by continuing business as usual; all hotels recorded and reported the amount of daily food waste.

Reducing plate size reduces food waste by 19.5%. Displaying signs encouraging guests to help themselves more than once reduces food waste by 20.5%. These reductions are significant, and there was no change in guest satisfaction observed during the treatment period.

Inspired to implement this design in your own work? Here are some things to think about before you get started:

• Are the behavioral drivers to the problem you are trying to solve similar to the ones described in the challenge section of this project?
• Is it feasible to adapt the design to address your problem?
• Could there be structural barriers at play that might keep the design from having the desired effect?
• Finally, we encourage you to make sure you monitor, test and take steps to iterate on designs often when either adapting them to a new context or scaling up to make sure they’re effective.

Additionally, consider the following insights from the design’s researchers:

• The researchers did not test using both measures jointly – reducing plate size and showing the social cue posters at the same time, so their combined effect is still unknown.
• The signs should be placed at the buffet where every guest can easily see them. Use multiple languages to reach diverse hotel guests.
• In a complementary observational study of plate size among the untreated hotels, researchers found that a 1 cm reduction in plate size reduces food waste by 2.5 kg, or 7.4%.
• To evaluate the impact of their intervention, researchers controlled for pre-treatment differences between the hotels and for time trends that are unrelated to the intervention. They also controlled for the number of guests staying at the hotel and food sales revenue.