A modified Delphi to inform development of a multidimensional diet quality score for a sustainable healthy diet

No existing dietary metric simultaneously captures key dimensions of sustainable healthy diets: dietary variety; intake of animal products; and extent of food processing. This methods and construct development study aimed to identify indicators of a sustainable healthy diet that can be used to inform a multidimensional diet quality score. A modified Delphi was used to gain expert consensus regarding development of a sustainable healthy diet score. Three iterative surveys were conducted between November 2022 and May 2023. Surveys asked participants’ opinion regarding measurement of the three dimensions of sustainable healthy diets (Dimension 1: variety of unprocessed and minimally processed foods; Dimension 2: intake of animal products and; Dimension 3: intake of ultra-processed foods (UPF)) and weighting and aggregation of a score that assesses these three dimensions. Thirteen international experts completed all three surveys. Consensus from experts led to the identification of food-based indicators of sustainable healthy diets. Experts agreed that Dimension 1 should be comprised of 12 food groups, with food groups and scoring ranges informed by the Global Diet Quality Score; Dimension 2 comprised of five food groups with scoring ranges informed by the EAT-Lancet planetary health diet; and Dimension 3 as one food group measured as a cut-off value of ≤10% energy from UPF. There was consensus that each dimension should be equally weighted. Outcomes from this work have been used to inform the development and validation of a multidimensional diet quality score to assess the healthfulness and environmental sustainability of diets among healthy adult populations.