There is mounting interest in the dual health and environmental benefits of plant-based diets. Such diets prioritise whole foods of plant origin and moderate (though occasionally exclude) animal-sourced foods. However, the evidence base on plant-based diets and health outcomes in Australasia is limited and diverse, making it unsuitable for systematic review. This review aimed to assess the current state of play, identify research gaps, and suggest good practice recommendations. The consulted evidence base included key studies on plant-based diets and cardiometabolic health or mortality outcomes in Australian and New Zealand adults. Most studies were observational, conducted in Australia, published within the last decade, and relied on a single dietary assessment about 10–30 years ago. Plant-based diets were often examined using categories of vegetarianism, intake of plant or animal protein, or dietary indices. Health outcomes included mortality, type 2 diabetes and insulin resistance, obesity, cardiovascular disease, and metabolic syndrome. While Australia has an emerging and generally favourable evidence base on plant-based diets and health outcomes, New Zealand’s evidence base is still nascent. The lack of similar studies hinders the ability to judge the overall certainty of evidence, which could otherwise inform public health policies and strategies without relying on international studies with unconfirmed applicability. The proportional role of plant- and animal-sourced foods in healthy, sustainable diets in Australasia is an underexplored research area with potentially far-reaching implications, especially concerning nutrient adequacy and the combined health and environmental impacts.

Systems thinking is deeply rooted in history, as far back as Aristotle. However, it has only relatively recently reemerged as an approach to help us understand and intervene in health and food systems. This is particularly salient, given its impact on environmental and population health. Whilst global food is abundant, many people cannot access affordable, healthy and culturally appropriate food. On the other hand, foods of low nutrient density are widely available. Food systems are complex and require complex thinking and approaches that allow us to consider the influence of multiple factors and how the might system respond to change. In turn, this enables the identification of ‘leverage’ points, where policies or interventions are most likely to have a sustained impact. The Foresight obesity map inspired others to adopt systems approaches to help understand the broader social, economic, environmental determinants of obesity to support intervention/policy development. Evaluation of these requires a consideration of complexity to explore why intervention goals may or may not have been successful and how relationships between components or approaches can be enhanced to support implementation and thereby increase the potential for effectiveness. Overall, approaches to understand, intervene, govern and evaluate food systems must themselves be sufficiently complex, or will ultimately be destroyed by the system it seeks to improve. This review paper aims to introduce readers to the application of systems approaches in research within the context of food systems and health, including its traditional/historical origins.