Cross-sectional measurement of adherence to a proposed sustainable and healthy dietary pattern among United States adults using the newly developed Planetary Health Diet Index for the United States

Dietary choices are an important avenue for improving food system sustainability. The Planetary Health Diet was proposed by the EAT-Lancet Commission as a reference healthy and sustainable dietary pattern. To assess adherence to the Planetary Health Diet among United States adults, this study developed and evaluated the Planetary Health Diet Index for the United States (PHDI-US), adapted from the original PHDI validated in the Brazilian population. The PHDI-US has 16 components with scores ranging between 0 and 150, and higher scores indicate better adherence to the Planetary Health Diet. Cross-sectional dietary data from 4741 participants of the National Health and Nutrition Examination Survey 2017–2018 were used to assess the validity and reliability of the PHDI-US. Validity and reliability tests were acceptable overall: principal component analysis identified 6 components; total PHDI-US and Healthy Eating Index-2015 scores were positively associated (β = 0.67, standard error = 0.03, P <0.0001; R2 = 0.39); concurrent-criterion validity analyses identified significantly lower scores among males, everyday smokers, and younger adults; and the Cronbach's α value was 0.54. The average PHDI-US score was 46.7 out of 150, indicating that the diets of United States adults were far from meeting Planetary Health Diet recommendations. Based on component PHDI-US scores, many United States adults may be able to enhance the quality and sustainability of their diets by increasing intake of plant-based foods, including whole grains, nuts and peanuts, legumes, fruits, and vegetables, and reducing intake of animal-based foods, including red and processed meats. The PHDI-US is a new tool that can assess adherence to the Planetary Health Diet and identify key aspects of United States adults' diets that could be altered to potentially improve dietary sustainability and quality.