The food system is a major source of both environmental and health challenges. Yet, the extent to which policy-induced changes in the patterns of food demand address these challenges remains poorly understood. Using a survey-based, randomized controlled experiment with 5,912 respondents from the United Kingdom, we evaluate the potential effect of carbon and/or health taxes, information and combined tax and information strategies on food purchase patterns and the resulting impact on greenhouse gas emissions and dietary health. Our results show that while information on the carbon and/or health characteristics of food is relevant, the imposition of taxes exerts the most substantial effects on food purchasing decisions. Furthermore, while carbon or health taxes are best at separately targeting emissions or dietary health challenges, respectively, a combined carbon and health tax policy maximizes benefits in terms of both environmental and health outcomes. We show that such a combined policy could contribute to around one third of the reductions in residual emissions required to achieve the United Kingdom’s 2050 net-zero commitments, while discouraging the purchase of especially unhealthy snacks, sugary drinks and alcohol and increasing the purchase of fruit and vegetables.