Aligning Environmental Sustainability, Health and Affordability in Diet Quality: A Systematic Review

BACKGROUND: Improving population health while simultaneously respecting planetary boundaries is of critical interest globally. Despite this shared motivation, research on the dietary changes required continues to operate in silos, focusing on certain pairings (diet-climate), rather than examining sustainable diets in their totality. This review aimed to summarise the literature on adherence to a priori defined dietary patterns in consideration of diet quality, environmental impacts, metabolic risk factors for non-communicable diseases (NCDs), and affordability. METHODS: Following the PRISMA guidelines, the review protocol was registered prospectively with PROSPERO. Seven electronic databases were searched as of October 2022. Two reviewers independently screened abstracts for inclusion, followed by full-text. One reviewer conducted data extraction and a quality assessment of eligible articles. RESULTS: Twenty-four studies were included with the majority from European countries (n = 22), and two from Australia. Thirteen distinct diet quality scores were identified, with those measuring adherence to national dietary guidelines the most reported. Thirteen distinct environmental impact indicators were identified, with greenhouse gas emissions (GHGE) (n = 23) assessed most. Indicators to assess impact on biodiversity were reported least. All studies reported on Body Mass Index (BMI) and seven on the daily cost of dietary adherence. Higher quality diets assist with maintaining a healthy weight and reducing environmental impacts, however, incongruities between population and planetary health can occur, especially between plant food consumption and water footprint. Further, sustainable diets can increase financial cost. CONCLUSIONS: Higher diet quality can reduce planetary pressures, however lower impact diets are not inherently nutritionally optimal. Higher quality, low environmental impact diets may provide a protective role against risk of obesity, but have affordability implications. KEY MESSAGES: • Diets providing synergies between health and multiple environmental concerns requires continued research, with specific focus on the socio-cultural and economic dimensions of sustainable diets. • Public health strategies to confront the Global Syndemic should greater emphasise the win-win outcomes for population and planetary health through dietary change in higher-income countries.