In a recent study published in The American Journal of Clinical Nutrition, a gaggle of researchers utilized the newly developed Planetary Health Diet Index for the US (PHDI-US) to guage adherence to the Planetary Health Diet and discern crucial areas for improvement in U.S. adults’ diets to reinforce dietary sustainability and quality.

Study: Cross-sectional measurement of adherence to a proposed sustainable and healthy dietary pattern amongst U.S. adults using the newly developed Planetary Health Diet Index for the US. Image Credit: j.chizhe Shutterstock

Background 

The worldwide food system, a major contributor to climate change, calls for revolutionary, sustainable dietary solutions, particularly given the substantial environmental impacts of animal-based foods, predominantly occurring on the farm stage. The EAT-Lancet Commission has proposed the Planetary Health Diet to mitigate such impacts, emphasizing the consumption of plant-based foods. PHDI measures adherence to this eating regimen but requires validation and adaptation for the U.S. population. Developing a tailored PHDI-US is pivotal to assessing and enhancing adherence, addressing disparities in dietary sustainability and health quality, and informing subsequent interventions, endorsing global environmental conservation. Further research is crucial for adapting such tools for diverse populations, facilitating sustainable and healthy dietary practices, promoting food security, and contributing to global environmental preservation.

Concerning the study

The study analyzed data from the National Health and Nutrition Examination Survey (NHANES) 2017-2018 participants, prioritizing individuals aged 20 or older and dismissing unreliable dietary recalls. Utilizing a complicated, multi-stage probability sampling, dietary information was acquired via computer-assisted, in-person interviews specializing in 24-hour dietary recall. 

The Food Patterns Equivalent Database 2017-2018 quantified intake, which informed PHDI-US components, encompassing sixteen components with a maximum rating of 150. The modifications ensured the compatibility of PHDI-US with various dietary intakes, making it a more inclusive tool. Adjustments included accommodation for vegan and vegetarian diets, substituting certain components with plant proteins and fortified soymilk, and including palm oil within the Saturated Fats component.

Statistical analyses conducted via SAS software and adhering to NHANES procedures concluded that p-values <0.05 were significant. The study meticulously evaluated the U.S. population's adherence to the Planetary Health Diet, applying descriptive statistics, independent t-tests, and Bonferroni corrections. Construct and concurrent-criterion validity was assessed through various scientific methods, ensuring the reliability of PHDI-US in measuring dietary sustainability and quality. This comprehensive approach reaffirms the adaptability and alignment of PHDI-US with the Planetary Health Diet, contributing significantly to environmental conservation and global health initiatives.

Study results

In an in-depth evaluation of the entire PHDI-US scores, substantial disparities in variations were revealed across different race or ethnicity groups; Non-Hispanic Asian individuals achieved the best mean total rating at 56.0±1.24, whereas Non-Hispanic Black individuals scored significantly lower, with a mean rating of 41.9±0.78. This lower rating was prevalent across all racial or ethnic groups except the “Other” race group, with a mean rating of 46.1±1.31 (p = 0.0101). 

An intriguing pattern was observed when analyzing PHDI-US scores together with the Participant Income Ratio (PIR). Scores were found to generally escalate with increasing income levels. Notably, individuals in the best PIR group obtained a PHDI-US rating of 48.5±0.72, significantly surpassing the 1.31-2.50 PIR group, which scored 44.8±0.52 (p = 0.0004). Linear regression analyses revealed that nutrients predominantly present in animal-based foods were inversely related to PHDI-US scores, while those abundant in plant-based foods showed a positive correlation. Surprisingly, polyunsaturated fat didn’t significantly correlate with total PHDI-US scores.

The excellent linear regression evaluation identified low yet meaningful correlations between nutrient intake and total PHDI-US scores. Nutrients inherent in animal-based foods, comparable to cholesterol, vitamin B12, and saturated fat, shared a negative association with total PHDI-US scores, suggesting a lower consumption of such nutrients could yield higher adherence to a planetary health eating regimen. Conversely, nutrients abundant in plant-based foods, namely, vitamin C and fiber, were positively related to PHDI-US scores, indicating the next consumption correlates with adherence to the planetary health eating regimen. 

The Principal Component Evaluation and linear regression displayed a couple of linear combination of PHDI-US components significantly contributed to data covariation. Moreover, the entire healthy eating index (HEI)-2015 and PHDI-US scores demonstrated a significantly positive association (ß = 0.67, SE = 0.03, p <0.0001; R2 = 0.39). Notably, individuals who abstained from smoking achieved significantly higher mean total PHDI-US scores in comparison with regular smokers (p <0.0001). Female participants and older participants, particularly those aged 60 and above, also exhibited significantly higher mean total PHDI-US scores.

To judge internal consistency among the many sixteen PHDI­-US components, Cronbach’s alpha was applied, yielding a price of 0.54. Correlations between PHDI-US components were mostly significant but low, ranging between 0.000 and 0.387. The item-total correlations between the components and total PHDI-US scores were significant and customarily moderate, starting from 0.165 to 0.452. These analyses have provided nuanced insights into the relationships between eating regimen, demographic aspects, and adherence to the principles of the Planetary Health Diet, contributing to an understanding of sustainable eating patterns and dietary intake.