Food systems around the world are in crisis. They are fostering dietary patterns associated with dietary risk factors, which are among the leading contributors to the global (and national) burden of disease.1 Worryingly, trend data indicate the global prevalence of all forms of malnutrition is moving in the wrong direction, casting increasing doubt that the food and nutrition-related Sustainable Development Goals will be met by 2030.2 Food systems also are unsustainable. Their profligate use of finite resources and substantial production of waste is threatening humanity's ability to live within planetary boundaries.3 Within food systems, there is a bi-directional relationship between dietary consumption patterns and food supply sustainability.4 On the one hand, the dietary patterns being fostered by food systems are responsible for one third of global greenhouse gas emissions5 and approximately 70% of freshwater use6 as well as being the primary drivers of biodiversity loss.7 Modelling indicates that dietary consumption patterns alone could add nearly 1°C to global warming by the end of the century8 and this will severely undermine attempts to keep global temperatures below the 1.5°C increase identified as tolerable by the Paris Agreement.9 On the other hand, transcending planetary boundaries will compromise the ability of food systems to supply sufficient amounts and variety of nutritious food to support the food and nutrition security of populations. In relation to climate change alone, the Intergovernmental Panel on Climate Change states with ‘high confidence’ that ‘the impacts of climate change on food availability and nutritional quality will increase the number of people at risk of hunger, malnutrition and diet-related mortality’.10 Mechanisms for explaining these climate change impacts are being identified and modelled. For example, experimental trials in which crops were grown under a CO2 level of 550 ppm, similar to that projected for 2050, recorded 3%–17% lower concentrations of protein, iron and zinc.11 There is an increasing urgency to calls from nutrition scientists to change current food systems, so they become healthy and sustainable and thereby support the achievement of global environmental targets, such as the Paris Agreement9 and the Sustainable Development Goals.12 Sustainability in a food systems context has been defined by the High Level Panel of Experts on Food Security and Nutrition of the Committee on World Food Security as, ‘Food system practices that contribute to long-term regeneration of natural, social and economic systems, ensuring the food needs of the present generations are met without compromising the food needs of future generations’.13 The overwhelming majority of nutrition and dietetic experts recognise that a ‘business as usual’ approach towards the structure and operation of food systems is not tenable. What is less clear is the ‘order’ of food system change that is necessary. Some people believe that a first-order (adjustment/tweak/nudge) change to food systems will be sufficient, for example, food label information and food reformulation interventions managed by a health department. Others believe that a second-order (reform) change to food systems is needed, for example, coordinated food procurement, fiscal and regulation interventions across government departments to replace the proliferation of ultra-processed foods with a higher proportion of accessible, available and affordable minimally processed foods in the marketplace. Still others believe that a third-order (transformation) change to food systems is necessary, for example, a whole-of-government commitment to a national food and nutrition policy to fundamentally re-frame the purpose of, and power relationships within, food systems. It was this transformational order of change that was the focus of the United Nations Food systems Summit 2021.14 A strategic combination of all orders of food system change has been proposed as a necessary approach to transitioning to healthy and sustainable food systems and dietary patterns.15 Dietitians are particularly well-placed to take a leadership role in changing food systems. We have training in nutrition science, practical skills in food and nutrition, experience in communicating food and diet information, and often work in multi-disciplinary teams. Critically, an increasing number of dietitians are also demonstrating advanced and specialised competencies in food policy, regulation, and advocacy for change. There are still competencies to mainstream to a greater extent than is evident at present. In the future, an essential competency for dietitians working to promote and protect healthy and sustainable diets and food systems MUST be a deep understanding of ecological nutrition concepts as a basis to analysing the health and sustainability potential of food systems. Progress towards promoting healthy and sustainable food systems has already been made by many dietitians and Dietitians Australia. In recent years, the Dietitians Australia Food and Environment Interest Group has released its Food Systems and Environmental Sustainability Role Statement,16 sustainability has been incorporated into the National Competency Standards for Dietitians in Australia17 and Dietitians Australia has published its Position statement on healthy and sustainable diets.18 In academia and professional training activities more broadly, there are exciting activities underway with innovative curriculum design and resource development to support dietitians in tackling health and sustainability challenges. The diversity of nutrition and dietetics research projects investigating healthy and sustainable food systems is well illustrated by the studies reported in this issue of Nutrition & Dietetics. There is a coverage of health and sustainability aspects of food systems within health care settings. Collins and Porter19 report on the results of their audit of food and food packaging waste produced in hospital foodservice. The scale of this problem is starkly highlighted by their finding that, on average, across the three hospital foodservices they audited, there was 502.1 kg/day of waste, which then is usually sent to landfill. Complementing this work, Lewandowski et al.20 in a separate paper report on findings from a pilot study investigating the safety, operational feasibility and environmental impact of collecting unopened non-perishable packaged hospital food items for reuse. They found a substantial volume of unused packaged hospital food collected from trays was safe, indicating that reusing many non-perishable packaged food items might be one strategy to divert some food waste from landfill. In a related systematic review, Cook et al.21 describe food and food-related waste management strategies in hospital food services. The review reports that the most frequently reported approaches to divert food and food-related waste from landfill included composting, donating surplus food, and industrial use. A significant contributor to food waste and inefficient food provision in food service settings is food supply chain disruptions. The COVID-19 pandemic provides a salient lesson in how suddenly food supply chain disruptions can arise. Cook et al.22 report that despite COVID-19 adversely impacting food service operations, food waste and labour shortages, foodservices can be highly adaptable and transition rapidly in times of unanticipated food supply chain disruption. In her letter published in this issue, Kennewell23 reflects on her experiences when developing a meal service model for people placed in mandatory COVID-19 hotel quarantine. She describes lessons for dietitians who might be required to respond to future food system shocks—an increasingly plausible scenario with sustainability-associated challenges across food supply chains. One of the more complex and controversial topics within the healthy and sustainable diet literature is plant-based alternative protein foods. Two papers in this issue provide insights into this topic. Melville et al.24 report on a cross-sectional study that assessed the nutritional quality of plant-based meat analogues in Australia compared with equivalent meat products. They found that most meat analogues are ultra-processed, vary in their nutrient content and few are fortified. Riddout25 notes the current uncertainty about the environmental profiles of foods derived from plant protein isolates and concentrates, engineered yeasts, cellular agriculture and insects. These uncertainties arise particularly because many of the processes used are proprietary, and voluntary reporting of environmental data is limited. He provides two powerful observations. First, the current information gaps ‘create a state of uncertainty about the actual environmental benefits and potential burden shifting from one environmental aspect to another’. Second, health and sustainability comparisons among foods ‘is a minefield ripe for cherry-picking of favourable data’. His letter proceeds to offer suggestions for addressing these uncertainties. Papers on two other important health and sustainability research topics are included in this issue. McCormack et al.26 report the findings from a scoping review investigating how dietetics students learn about sustainability. Disappointingly, just 12 articles have been published on this topic, and their synthesis revealed core gaps in teaching approaches as there was minimal reference to the Sustainable Development Goals and published sustainability guidelines. Masters et al.27 report on a cross-comparison evaluation of the environmental impacts and diet qualities of seven-day isocaloric diet models based on the Mediterranean, Atkins, Ornish, Zone diets, and the Turkiye Diet Guidelines-2015 recommendations. There are many opportunities for consolidating and expanding dietitians' roles and responsibilities as food systems change agents into the future. Encouragingly, positive activities are increasingly being undertaken by many dietitians. One innovative example is provided by Carino et al.28 in their letter in this issue describing the establishment and scope of a ‘Sustainable Food Systems Dietitian’ position created at a large metropolitan public healthcare network in Melbourne. The aim of this novel dietetics position was to embed environmental sustainability within patient foodservices using a multifaceted approach in collaboration with the foodservice, dietetics, and media and communications teams. Among many activities, it designed and implemented food waste and satisfaction audits to compare two existing foodservice models and planned a local food audit to map the origin of current food procurement. The authors emphasise that a sustainability dimension should be embedded into the responsibilities of clinical, foodservice, manager and student dietitian roles. Critically, they also comment on the need for training in environmental sustainability to be part of dietetics education, placements and professional development. It is pertinent to reflect on what might happen if dietitians are not engaged in food system change given there is currently no shortage of non-nutrition and non-dietetics opinions on food and nutrition. As Nourishing Australia notes, ‘There are many and varied groups that provide a “cacophony of noise” (my italics) from which consumers must synthesise the “truth” about food and nutrition’.29 With our nutrition science training, skills and understandings, I would argue dietitians can provide a ‘harmony of evidence-informed guidance’ to be lead change agents in promoting healthy and sustainable food systems. The author declares no conflict of interest.