Dietary patterns are prerequisites for health and integral components of ecological systems. For over a century researchers have been building a body of evidence of associations between dietary patterns and health and sustainability outcomes while policymakers have been synthesising and translating this evidence into policies to promote public health. During this period, food systems have dramatically changed and driven the emergence of food supplies and dietary behaviours with no ecological or evolutionary precedent. Now, the relevance of conventional nutrition research and policymaking approaches for understanding food system transitions and protecting against unhealthy and unsustainable diets is being questioned. This review aims to examine how the ecological nutrition paradigm might guide a transformed approach to nutrition research and policymaking to promote healthy and sustainable diets. It shows the ecological nutrition paradigm is transdisciplinary integrating biological, social and environmental dimensions into nutrition research and policymaking. The paradigm operates to a ‘fit-for-purpose’ policymaking orientation. It draws on ecological and evolutionary theories to provide insights to conceptualise the causes of, and solutions to, nutrition problems and help design relevant decision-making processes. These research and policymaking features contrast with the ‘one-size-fits-all’ policymaking orientation and prescriptive decision-making processes of the conventional medical nutrition paradigm. Their attention to a relevance criterion engenders confidence in the likely effectiveness, and ability to avoid unintended consequences, of policies informed within an ecological nutrition paradigm. The review proposes a shift to the ecological nutrition paradigm to transform nutrition research and policymaking for promoting healthy and sustainable diets is overdue.