Abstract
Background: The Planetary Health Diet Index (PHDI) is a novel measure adapted to quantify alignment with the dietary evidence presented by the EAT-Lancet Commission on Food, Planet, Health. Objectives: To examine how population-level health and sustainability of diet as measured by the PHDI changed from 2003 to 2018, and to assess how PHDI correlated with inadequacy for nutrients of public health concern (iron, calcium, potassium, and fiber) in the United States. Methods: We estimated survey-weighted trends in PHDI scores and median intake of PHDI components in a nationally representative sample of 33,859 adults aged 20+ y from 8 cycles (2003–2018) of the National Health and Nutrition Examination Survey with 2 d of dietary recall data. We used the National Cancer Institute method to examine how PHDI correlated with inadequate intake of iron, calcium, potassium, and fiber. Results: Out of a theoretical range of 0–140, the median PHDI value increased by 4.2 points over the study period, from 62.7 (95% confidence interval [CI]: 62.0, 63.4) points in 2003–2004 to 66.9 (66.2, 67.7) points in 2017–2018 (P-trend < 0.001), although most of this change occurred before 2011–2012 and plateaued thereafter. For adequacy components that are encouraged for consumption, nonstarchy vegetable intake significantly decreased over time, whereas whole grains, nuts and seeds, and unsaturated oils increased. For moderation components with recommended limits for consumption, poultry and egg intake increased, but red and processed meat, added sugars, saturated fats, and starchy vegetables decreased over time. Higher PHDI values were associated with a lower probability of iron, fiber, and potassium inadequacy. Conclusions: Although there have been positive changes over the past 20 y, there is substantial room for improving the health and sustainability of the United States diet. Shifting diets toward EAT-Lancet recommendations would improve nutrient adequacy for iron, fiber, and potassium. Policy action is needed to support healthier, more sustainable diets in the United States and globally.
Generated Summary
This research article analyzes the adherence to the Planetary Health Diet Index (PHDI) and its correlation with nutrients of public health concern in the United States, utilizing data from the National Health and Nutrition Examination Survey (NHANES) cycles spanning from 2003 to 2018. The study aimed to assess how population-level health and sustainability of diet, as measured by the PHDI, changed over this period. It also evaluated the correlation between PHDI and the inadequacy of key nutrients of public health concern, including iron, calcium, potassium, and fiber. The research employed survey-weighted trends in PHDI scores and median intake of PHDI components in a nationally representative sample of adults aged 20+ years. The National Cancer Institute method was used to determine how PHDI related to inadequate nutrient intake. The primary objective was to understand the alignment of the United States diet with the EAT-Lancet Commission’s recommendations for a universal healthy reference diet and to examine changes in dietary patterns and their impact on public health concerns over time. The study’s approach involved analyzing dietary recall data, deriving the PHDI, and assessing its correlation with nutrient adequacy, providing insights into the health and sustainability of the American diet in relation to global dietary guidelines.
Key Findings & Statistics
- The median PHDI value increased by 4.2 points over the study period, from 62.7 (95% confidence interval [CI]: 62.0, 63.4) points in 2003-2004 to 66.9 (66.2, 67.7) points in 2017-2018 (P-trend < 0.001).
- The estimated increase in median PHDI score was 0.38 (95% CI: 0.31, 0.44) points per survey cycle.
- The median PHDI score in quintile 1 increased by 4.2 points, from an estimated 47.3 (95% CI: 46.6, 48.1) in 2003-2004 to 51.5 (50.4, 52.6, P<0.001) in 2017-2018.
- For quintile 5, the median PHDI increased by 6.8 points, from an estimated 78.7 (77.7, 79.8) in 2003-2004 to 85.5 (84.2, 86.8) in 2017–2018.
- The prevalence of iron inadequacy was low (4.1%), whereas 43.5% of the population had inadequate calcium intake, 67.0% had inadequate potassium intake, and 92.3% had inadequate fiber intake.
- Consumption of non-starchy vegetables significantly decreased over time.
- There were modest but significant increases in whole grains, nuts and seeds, and added fat-unsaturated oils.
- Consumption of starchy vegetables, poultry, and eggs aligned with PHDI recommendations, whereas the intake of red and processed meat and added fat-saturated oils and trans fat were above PHDI recommendations.
- The median intake of starchy vegetables decreased over time.
- Consumption of poultry and eggs significantly increased.
- An inverse association was observed between PHDI quintile and probability of inadequate iron intake: 4.3% (3.8, 4.7) of those in quintile 1 had inadequate iron intake, compared with 3.1% (2.8, 3.3) of those in quintile 5 (P-trend < 0.01).
- For fiber intake, 99.8% (99.7, 99.9) of those in quintile 1 had inadequate fiber intake, compared with 73.7% (71.4, 76.0) of those in quintile 5 (P-trend < 0.001).
- The predicted probability of inadequate potassium was higher for quintile 1 [76.1% (73.8, 78.3)] than for those in the quintile 5 [51.0% (48.5, 53.5), P-trend < 0.001].
- The predicted probability of inadequate calcium intake was lower in PHDI quintile 1 [37.1% (35.1, 39.2)] than any other PHDI quintile [e.g., 44.3% (42.3, 46.3) for quintile 5, P < 0.001].
- In the 2017-2018 survey cycle, the median PHDI score was 66.9, less than half of the theoretical maximum score of 140.
- The study found disparities by income, education, and race/ethnicity.
- Higher income, college degree or greater, and Non-Hispanic White or Asian, Multiracial, and Other Non-Hispanic ethnicity were more likely to be in the highest PHDI quintile.
- The opposite was true for those with the lowest level of income and education and who self-identified as Non-Hispanic Black or Hispanic.
Other Important Findings
- The study found that improvements in PHDI score have stalled since the early 2010s.
- For moderation components, the United States is above targets for added sugars, added fat-saturated oils and trans fats, dairy, and red and processed meat, reflecting the typical “Western-style” dietary pattern.
- The United States diet is particularly high in terms of red and processed meat intake, with a median value of 65.9 g/d, approximately 5 times the 14 g/d proposed by the EAT-Lancet Commission.
- The study observed no change in dairy or red and processed meat intake, coupled with an increase in poultry and eggs.
- An inverse association between PHDI score and iron inadequacy was observed, suggesting that reducing animal-sourced foods without increasing anemia could improve health outcomes.
- Intakes of whole grains, nuts and seeds, fruits, and vegetables were below recommended amounts.
- Those with higher PHDI scores were less likely to have inadequate intakes of fiber and potassium.
Limitations Noted in the Document
- The study used 24-h dietary recalls, which cannot capture usual intake.
- The study did not account for the use of supplements in the adequacy analyses.
- The EAT-Lancet report published ranges of values for each component, but for simplicity, the study used the Report’s point estimates to calculate the score.
- The study was unable to account for changes because of the COVID-19 pandemic.
Conclusion
The research underscores that the American diet still significantly deviates from the EAT-Lancet Commission’s recommendations, with the PHDI score indicating that the diet aligns only partially with the guidelines. Despite some positive shifts over the two decades, particularly during the mid-2000s, the progress in improving dietary quality has plateaued. The overconsumption of moderation components, such as added sugars, saturated fats, and red and processed meats, alongside a relatively low intake of adequacy components like whole grains, fruits, and vegetables, is a defining characteristic of the United States diet. The inverse relationship between the PHDI score and iron inadequacy highlights the possibility of improving health outcomes by reducing animal-sourced foods without increasing anemia risk. The study reinforces the need for policy actions and public health efforts to facilitate a shift toward healthier and more sustainable diets in the United States. Addressing dietary disparities based on income, education, and race/ethnicity, promoting the consumption of whole grains, fruits, vegetables, and legumes, and reducing reliance on ultra-processed foods are critical steps. The findings emphasize the importance of aligning dietary guidelines with sustainability and health targets to tackle diet-related diseases and minimize environmental impacts effectively. The study concludes that substantial changes are necessary to transform food systems and accelerate the transition to sustainable diets for the population.