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Do default nudges increase plant-based milk consumption in Barjon?

Do default nudges work? In 2023, Marjon PhD student Katie Major-Smith conducted research investigating the effectiveness of applying plant-based milk as the default option and its ability to increase oat milk consumption (as opposed to cow's milk, which was the usual default option) in the local bar and café at Marjon. The baristas asked all customers if they had any allergies before serving them. Data was used from two sources to calculate the carbon footprint of milk consumption in Barjon: Both sources show that making oat milk the default milk option reduced average GHG emissions of milk consumption by 25-34%. The proportion of plant-based milk served in beverages rose, resulting in customers being three times more inclined to choose plant-based milk. Based on 1000 drinks per week, the 30% reduction is equivalent to one return flight from London to Rome.

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What Is a default nudge? 

A 'default nudge' is a strategy that helps shape people's behaviour using a specific design or approach. It involves using a default option which may guide people's choices for the better. Crucially, it should only be used to improve social conditions or environmental protection. The underlying concept is that when people are faced with decisions, they tend to stick with the default option or the choice that has already been pre-selected.

A barista at work in a coffee shop

The Results

The percentage of plant-based milk served in drinks increased when oat milk was the default milk option, with customers being three times more likely to consume plant-based milk. However, the percentage of plant-based milk consumed decreased slightly during the study, highlighting that we don’t know the long-term effectiveness of this nudge on plant-based milk consumption.


  • Making oat milk the default milk significantly increased plant-based milk consumption in Barjon. This supports the literature on plant-based food consumption (Meier et al., 2022; Hansen et al., 2021).
  • The oat milk default was well received by customers.
  • Defaults should be used by other UK university cafés to encourage plant-based milk consumption and help meet net-zero commitments.
  • But we don’t know its long-term effect and further research is needed on the long-term impact of default nudges.

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