“Dairy milk is available on request”: oat milk default halves dairy milk choices in cafés. 2 natural field and 1 online experiment.

Abstract

Diets in high-income countries need to shift from animal to plant-centric to meet climate change targets, improve human health, and reduce animal suffering. Hard regulation via bans and taxes, however, is politically difficult. Initial evidence found that setting more sustainable food options as the default option in out-of-home settings can be an effective yet liberty-preserving approach to reducing the consumption of animal products. We conducted 2 natural field experiments in the cafés of 2 universities in London over respectively 2 and 7 weeks to test whether reversing the default milk option from dairy to oat would significantly decrease dairy milk choices for milk-based barista drinks. Using data on 68,792 milk choices from 5 cafés, we estimated with a difference in difference technique that setting oat milk as the default milk option persistently decreased the percentage of dairy milk choices by respectively 23 and 55 points, with a symmetrical increase in oat milk choices. In the longer experiment, the intervention was not associated with any decrease in overall sales. In an online-based replication of the field experiments with university students (n = 212), we found that the effect was concentrated only in participants with weak relative preferences between dairy and oat milk. Additionally, we observed that over 75% of students would approve if university cafés switched their default milk option to oat milk. These results provide strong evidence that serving oat milk by default is an effective, low-cost, and viable strategy to reduce dairy milk consumption at scale.