Global diets and food systems,1 and the populations relying on them, are experiencing major challenges in terms of both health and sustainability which are predicted to worsen – models project that if global eating patterns do not change away from the current diets characterised by excess energy, processed-meat and refined sugar consumption (particularly in high income countries) and towards dietary patterns that are more rich in plant-based foods, half of the adult population and one-third of the total population (including children) will be overweight or have obesity by 2030.2 Current global food systems jeopardise climatic balance and ecosystem adaptability, as well as contribute to an estimated 11 million preventable adult deaths per year.3 In order for the projected 2050 global population of 10 billion people2 to have sufficient food to meet nutritional needs within the limits of the planet’s resources, the ways in which food systems operate must change, including which food is consumed and by whom.2-5 Recently released research has proposed a global diet which, if widely adopted, is predicted to help to alleviate these issues of malnutrition and unsustainability.3
2.1 The inherent link between food systems and climate change
Food insecurity6 is being exacerbated by climate change, with temperature changes, droughts and/or floods affecting food crops and consequently food accessibility in regions worldwide, including Australia.6-10 Increased carbon dioxide in the atmosphere also contributes to a reduction in the nutrient content of food,11-13 which could have widespread health implications for the global population, in particular those who are already struggling to consume enough quality food to meet their nutritional needs.6,13
The extent to which climate change will affect future food security remains uncertain,7,8 however, what is known is that while climate change affects food systems (e.g. in regard to the food able to be produced and the nutritional quality of this food), food systems also affect climate change (e.g. meat from ruminant animals contributing methane to greenhouse gas emissions),3,14 due to their mutually dependent relationship.8,14-17 Indeed, food production accounts for ≈30% of greenhouse gas emissions, ≈70% of water use, and ≈40% of land use globally.3 It is the largest cause of environmental damage and has the greatest effect on human and planetary health, but is also an area that we have a degree of control over to bring about positive change.3,18 In the EAT–Lancet Commission report,3 Willett et al. describe a Great Food Transformation that is predicted to result in healthier diets from sustainable food systems, for the benefit of the entire population and the planet. The need to transition to a more healthy and sustainable diet is echoed by organisations such as the Food and Agriculture Organization of the United Nations4,6,19 and the Food Climate Research Network (FCRN).20,21 The EAT–Lancet Commission report provides evidence that the most effective way to lessen the environmental impact of our food systems is to change our diet to a more sustainable one, such as the Planetary Health Diet (PHD) discussed further below.3,22
2.2 The Planetary Health Diet – both healthy and sustainable
A healthy and sustainable diet has been defined elsewhere but essentially is considered to be a diet that has low environmental impact while contributing to food security and meeting the health and nutritional needs of current and future generations.3,4,18,20,23-31 The Australian Dietary Guidelines (ADG), which have been criticised as having a reductionist approach to diet, consider nutrients first and foremost, not sustainability.32-34 It also places importance on animal-based proteins, so may not be the diet to propose as optimal especially given the demands on the food system of the consumption of the amount of meat recommended in the ADG. Australians generally consume a diet that is neither healthy nor environmentally sustainable,35,36 though to date few countries have adopted environmental sustainability as a focus in their dietary recommendations. In contrast, Sweden and Brazil are examples of countries who have already incorporated sustainability into their dietary guidelines by including recommendations such as a predominantly plant-based diet based on seasonal and local foods, reducing food waste, and reducing consumption of red and processed meat, ultra-processed foods, and sugar-sweetened beverages.19,37,38
The EAT–Lancet Commission’s report3 was the first to comprehensively integrate the nutritional needs of individuals with planetary sustainability principles into a single set of global dietary recommendations. The PHD reference diet39 is an example of a diet that is both healthy and sustainable. This reference diet forms the framework of the PHD recommendations and can be customised to regional cultural preferences.3 The PHD reference diet was analysed as being nutrient-sufficient, and modelling showed that the intake of most nutrients increased after adoption of this diet compared with current consumption patterns, with the exception of vitamin B12 which needs fortification or supplementation,3 consistent with the current general consensus on mostly plant-based diets.18,23,25,40 The EAT–Lancet Commission report stated that a global shift in dietary behaviours to align with the PHD could prevent around 19-23% of deaths per year (around 11 million deaths prevented) by way of improved human health,3 however under subsequent further analysis it appears that these prevented deaths may be purely the result of the changes in energy consumption associated with the PHD.41
2.3 Affordability as a factor affecting food choices
For the PHD to be widely adopted, it needs to be acceptable to consumers. While there are several factors that affect consumer food choices, such as accessibility, availability, health concerns and food preferences,2,42 this review considered the role of affordability as a key factor that may influence the uptake of the PHD.43 Cost is generally a major determinant of food choices,44-52 and, although health and sustainability are desired outcomes of consumer choices, affordability often takes priority, particularly for lower-income consumers.44,45,53-55 Therefore, it is necessary to understand the cost and affordability of a healthy and sustainable diet, such as the PHD, for a range of socioeconomic groups.
2.4 Is a healthy and sustainable diet affordable for Australians?
Presently, information about the affordability of healthy and sustainable diets is scant. Only one study appeared to exist on the affordability of a healthy and sustainable food basket across various socio-economic groups in an Australian context,46 but this was not undertaken nationally and the basket did not include the sustainability principles incorporated in the PHD. Studies also exist that have been undertaken in small regions in Australia such as specific metropolitan areas,46,56,57 but not nationally, meaning results cannot be applied to all areas in all states, and national comparisons between different areas in different states is not possible. To our knowledge, a healthy and sustainable food basket based on the PHD has not been created and analysed for affordability nationally across various socio-economic groups in Australia, however since the present study was completed, other research on the affordability of the PHD throughout the world has since been published.58 This is essential for measuring the affordability, and therefore the feasibility, of a healthy and sustainable diet for all Australians. Globally, two studies from United Kingdom have determined the cost of a healthy and sustainable diet and compared it to the typical diet consumed in that country.59,60
The aims of this study were to: (a) Determine the affordability of the PHD food basket for low, middle and high socio-economic groups in metropolitan Australia; (b) Determine if the PHD food basket is more or less affordable than the Typical Australian Diet (TAD) food basket for low, middle and high socio-economic groups in metropolitan Australia.