Encouraging healthy eating by appealing to environmental sustainability, health, or both: A randomized experiment with US young adults.

Objective: Diet quality is especially poor among young adults. Messages could encourage young adults to eat more healthfully, but it remains unclear whether messages appealing to sustainability, health, or both are most promising. Methods: In 2024, US young adults (n = 1732) ages 18-25 completed a between-subjects experiment in which they were randomized to messages about 1) sustainability, 2) health, 3) sustainability + health, or 4) control. Participants viewed messages from their assigned condition promoting four healthy dietary substitutions shown in random order: replacing beef and pork with chicken or vegetarian options, dairy milk with non-dairy milk, juice with fruit, and sugary drinks with water. Participants rated each message on perceived message effectiveness using a four-item scale. Results: Across all substitutions, the sustainability, health, and sustainability + health messages were perceived as more effective than control messages (ps < 0.01). For the beef and pork and milk substitutions, all topics were perceived as similarly effective (ps ≥ 0.45). For the juice substitution, sustainability + health messages outperformed sustainability messages (p = .02) and for the sugary drink substitution, both health messages and sustainability + health messages outperformed sustainability messages (ps ≤ 0.01). Conclusions: Messages appealing to environmental sustainability, health, or both could encourage young adults to adopt healthy dietary substitutions.