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Observational Study
. 2019 Oct 15;116(42):20923-20929.
doi: 10.1073/pnas.1907207116. Epub 2019 Sep 30.

Impact of increasing vegetarian availability on meal selection and sales in cafeterias

Emma E Garnett  1 , Andrew Balmford  2 , Chris Sandbrook  3 , Mark A Pilling  4 , Theresa M Marteau  4
Affiliations
Observational Study

Impact of increasing vegetarian availability on meal selection and sales in cafeterias

Emma E Garnett et al. Proc Natl Acad Sci U S A. .

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.

Keywords: behavior change; choice architecture; climate change; diet; meat.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Overview of data and levels of analyses in study 1 and study 2. Image credit: Icons from the Noun Project (https://nounproject.com).
Fig. 2.
Fig. 2.
Effects of vegetarian availability on vegetarian and total sales for study 1. (A) Raw values (jittered) of vegetarian sales against vegetarian availability. (B and C) Modeled likelihood of selecting a vegetarian meal for individual diners at colleges A and B, with individual diners divided into least vegetarian (LeastVeg) to most vegetarian (MostVeg) quartiles. LessVeg, less vegetarian; MoreVeg, more vegetarian. (D) Raw values (jittered) of total sales against vegetarian availability. Lines of best fit and CIs were generated from the models using conditional regression and the visreg package in R (Methods).
Fig. 3.
Fig. 3.
Effects of vegetarian availability on vegetarian and total sales for college C, study 2. (A) Raw values of vegetarian sales against vegetarian availability. (B) Modeled likelihood of selecting a vegetarian meal for individual diners, divided into least vegetarian (LeastVeg) to most vegetarian (MostVeg) quartiles. LessVeg, less vegetarian; MoreVeg, more vegetarian. (C) Raw values of total sales against vegetarian availability. (D) Raw values of vegetarian sales at dinner during the control and experimental weeks, with model mean estimates and CIs shown in white. Lines of best fit and CIs in A and C and model mean estimate with CIs in D were generated from the models using conditional regression and the visreg package in R (Methods).
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