Abstract
Shifting people in higher income countries toward more plant-based diets would protect the natural environment and improve population health. Research in other domains suggests altering the physical environments in which people make decisions (“nudging”) holds promise for achieving socially desirable behavior change. Here, we examine the impact of attempting to nudge meal selection by increasing the proportion of vegetarian meals offered in a year-long large-scale series of observational and experimental field studies. Anonymized individual-level data from 94,644 meals purchased in 2017 were collected from 3 cafeterias at an English university. Doubling the proportion of vegetarian meals available from 25 to 50% (e.g., from 1 in 4 to 2 in 4 options) increased vegetarian meal sales (and decreased meat meal sales) by 14.9 and 14.5 percentage points in the observational study (2 cafeterias) and by 7.8 percentage points in the experimental study (1 cafeteria), equivalent to proportional increases in vegetarian meal sales of 61.8%, 78.8%, and 40.8%, respectively. Linking sales data to participants’ previous meal purchases revealed that the largest effects were found in the quartile of diners with the lowest prior levels of vegetarian meal selection. Moreover, serving more vegetarian options had little impact on overall sales and did not lead to detectable rebound effects: Vegetarian sales were not lower at other mealtimes. These results provide robust evidence to support the potential for simple changes to catering practices to make an important contribution to achieving more sustainable diets at the population level.
Generated Summary
This research investigates the impact of increasing vegetarian meal availability on consumer choices and sales in three university cafeterias. Employing both observational and experimental methods over a year-long period, the study aimed to determine if increasing the proportion of vegetarian options influenced meal selection and overall sales. The research design included an observational study across two colleges (Study 1) and an experimental study in a third college (Study 2), where the number of vegetarian options was systematically varied. The central hypothesis tested was that increasing the availability of vegetarian options would increase their selection by diners. The study’s approach involved collecting and analyzing anonymized individual-level data on meal purchases, allowing the researchers to assess the effects of vegetarian availability on vegetarian meal sales, total meal sales, and potential rebound effects. The methodology included the use of linear models (LMs), binomial generalized linear models (GLMs), and binomial generalized linear mixed models (GLMMs) to analyze aggregate and individual-level data, controlling for various factors such as the day of the week, temperature, and price differences between vegetarian and meat options.
Key Findings & Statistics
- Impact of Increasing Vegetarian Availability on Sales: Doubling the proportion of vegetarian meals available from 25% to 50% increased vegetarian meal sales by varying degrees in different settings.
- Observational Study (Study 1): In the observational study, the increase in vegetarian options resulted in a 61.8% increase in vegetarian meal sales in college A and a 78.8% increase in college B.
- Experimental Study (Study 2): The experimental study showed a 40.8% increase in vegetarian sales when the availability was doubled.
- Vegetarian Sales and Availability Correlation (Study 1): In study 1, vegetarian availability alone explained 20.9% and 31.9% of the variation in vegetarian sales at college A and college B, respectively. After controlling for other variables, the best-fit models explained 26.1% and 39.3% of the variability in vegetarian sales at colleges A and B, respectively.
- Vegetarian Sales and Availability Correlation (Study 2): Vegetarian availability explained 3.9% of the variation in vegetarian sales. After controlling for other variables, 31.8% of the variation was explained, and availability remained a highly significant predictor.
- Impact on Total Sales: Increasing vegetarian availability had no significant impact on total sales in college A and a small negative effect in college B. In college B, total meals sold decreased from 138 to 128 as vegetarian availability increased from 25% to 50%.
- Effect on Diners’ Behavior: The quartile of diners with the lowest prior levels of vegetarian meal selection showed the largest response to increased vegetarian availability.
- Rebound Effects: In study 2, no evidence of rebound effects was found; vegetarian sales at dinner did not decrease during weeks when there were higher vegetarian sales at lunch.
Other Important Findings
- The research revealed that increasing the availability of vegetarian options directly correlated with an increase in the selection of vegetarian meals.
- The study indicated that the impact of increasing vegetarian availability was most pronounced among individuals who had the lowest prior consumption of vegetarian meals.
- The study found little or no impact on overall sales, suggesting that this strategy does not necessarily deter overall consumption.
- There were no detectable rebound effects, indicating that increased vegetarian choices did not lead to increased meat consumption at other times.
- In Study 1, other factors like price and ambient temperature correlated with vegetarian sales, though the effects varied between the two colleges.
- In Study 2, when examining total meals sold, increasing the availability of vegetarian meals showed no significant effect.
- The study suggests the intervention could serve as a cost-effective strategy to promote sustainable eating habits.
Limitations Noted in the Document
- The study’s data collection was confined to a university setting (students and staff), and the findings’ generalizability to other populations remains uncertain.
- The research did not assess the nutritional content or palatability of the vegetarian meals, which could affect consumer choices.
- Some misclassification of vegetarian meals as meat meals occurred, potentially underestimating the impact of increased vegetarian availability.
- The experimental study (Study 2) had limitations, as the alternation between one and two vegetarian options could not be strictly followed due to operational constraints.
- The study acknowledges the necessity for future research to explore the economic aspects of increasing vegetarian meal sales, including the impact on profits and labor costs.
- Data was collected over a specific period, and the long-term effects on consumer behavior were not evaluated.
Conclusion
The study’s findings demonstrate that increasing the availability of vegetarian options in cafeterias is an effective strategy for promoting more sustainable diets. The results indicate that doubling the proportion of vegetarian meals can significantly increase vegetarian meal sales, without negatively impacting overall sales. This approach, which the authors term “choice architecture,” offers a relatively inexpensive and easily implemented method to encourage more sustainable eating habits. The study highlights the importance of targeting interventions toward those with lower prior levels of vegetarian consumption, as they showed the most significant behavioral changes in response to increased availability. The study underscores the potential of altering the physical environment where people make decisions (choice architecture) to achieve socially desirable behavior changes. It suggests that by making vegetarian options more accessible, cafeterias can contribute to significant reductions in meat consumption, thereby positively impacting both environmental sustainability and public health. The authors emphasize that the findings have the potential to contribute to global efforts to promote more sustainable diets by supporting the global ambition for more sustainable diets. The study also noted that to achieve broader environmental benefits, dietary changes must extend to the agricultural production systems, requiring both dietary shifts and agricultural innovations. The study’s conclusion emphasizes that interventions like this can substantially reduce meat consumption, even for individuals with lower baseline levels of vegetarian meal selection. Further, the intervention could be a scalable, low-cost approach to change behavior in settings beyond universities and potentially be effective in a variety of contexts, including those in middle- and low-income countries. The study’s results support that caterers, by providing more plant-based options, are not merely responding to but actively shaping consumer demand.