The current food system is unsustainable. It encourages unhealthy food choices, increasing the risk of non-communicable diseases, and has a substantial environmental impact, responsible for around a third of all anthropogenic greenhouse gas emissions. Improving both public and planetary health will require dietary change. To promote this transition, it is crucial to understand how consumers conceptualise healthy and sustainable eating. The aim of this review was to examine how adults from high-income countries interpret healthy and sustainable eating, with a specific focus on Ireland and the UK. As healthy eating and sustainable eating are often conceptualised as distinctive constructs, we explored each of these separately before examining how consumers perceive them together. Most consumers have a reasonable understanding of what constitutes a healthy diet, with many echoing aspects consistent with dietary guidelines. However, consumers perceptions of healthy eating often extend beyond these health-centric recommendations, incorporating concepts such as the pleasure of eating and supporting mental well-being. Sustainable eating, on the other hand, is less well understood. Most consumers overemphasise the importance of eating local, organic food and reducing packaging and underestimate or are unaware of the environmental impact of red meat consumption. These findings provide a clear opportunity to improve public awareness of healthy and sustainable diets. Moreover, they emphasise the need to promote the synergies between healthy and sustainable dietary practices. However, knowledge alone will not be enough to change behaviour. Future interventions should also seek to overcome consumers competing dietary priorities and create system-wide changes.