Using the planetary-health diet index to assess how USA diets have transitioned toward sustainable rating

This study aimed to examine how population-level health impacts and environmental sustainability of United States diets have changed from 2003-2018.

It also used PHDI (a novel index based on evidence presented by the EAT-Lancet commission) to assess how it correlates with nutrients of public health concern (iron, calcium, potassium and fibre).

Method

The study utilised data for adults (>20 years) from national survey data (2003-2018).

Dietary intake was assessed via 24-h recall, scored against EAT-Lancet Commission guidelines.

The PHDI scoring criteria was then derived from the reported intake of 14 food groups in accordance with the recommended intake listed in the EAT-Lancet commission.

For each food group participants scored between 0 (minimum) and 10 (maximum) with a maximum possible score of 140.

Sociodemographic variables were collected and used as covariates to improve precision of estimation.

Quantile regression analysed PHDI trends, adjusting for total energy intake.

Key findings

The typical US diet, based on this sample, does not align with principles of EAT-Lancet

The median PHDI in the final 2017-18 cycle was 66.9, less than half the theoretical maximum score. There was only a 4.2-point increase from the 2003-4 cycle and on closer consideration, improvements in congruence with the PHDI index have largely stalled since the early 2010s.

This low score is driven in part by high red and processed meat consumption with a median value 5x greater than the 14g/day recommendation.

There has been no change in consumption of these products over the course of this study period. There has also been an increase in poultry and egg consumption.

Additionally, under consumption of wholegrains, nuts and seeds is observed. These values have increased over the course of the study.

Conversely, already low values in fruit and non-starchy vegetables continue to decrease, for example, non-starchy vegetables decreased from 136.2g to 118.7g (p=<0.001)

Large disparities due to covariates of income, education and race were present.

Micronutrient considerations

In relation to the above, there was also significantly low mean intakes of fibre and potassium in the population across the study time period:

• 92.3% had inadequate fibre intake

• 67.0% had inadequate potassium intake

• 4.1% had inadequate iron intake

Higher PHDI quintiles (Q) show mostly improved levels of micronutrients of concern:

• Fibre: in Q1 (low PHDI), 99.8% had inadequate intake of fibre compared to 73.7% in Q5 (high PHDI).

• Potassium: 76.1 were deficient in calcium intake in Q1 vs 51.0% in Q5.

• Iron: 4.3% of participants in PHDI Q1 were insufficient in iron intake. Comparatively, Q5 had only 3.1% iron insufficiency. However, this does not account for differences in bioavailability.

Calcium found a converse relationship, with 7.2% greater insufficiency in the highest PHDI scores compared to the lowest quintile.

Calcium is a nutrient of concern, but many vegetables, seeds, and legumes have greater calcium density and bioavailability than dairy products, posing an area for improvement.

Conclusion

This paper is the first to use a novel measure of adherence to the EAT-Lancet guidance in the form of the PHDI.

It provides useful insight into the current state of nutritional intake in relation to the planetary health diet as well as historical changes or lack thereof. Future studies should use the PHDI or similar to allow for comparison between populations.