A high Planetary Health Diet Index (PHDI) was associated with a reduction in mortality and with a lower environmental impact compared to a low PHDI, according to a recent study in the USA (1).
The study conducted by Bui et al. included data from three cohorts of health workers, with more than 206,000 participants, and showed a negative association between a high PHDI and death by any cause.
What is the Planetary Health Diet Index developed in the study?
The PHDI was created to describe adherence to the EAT-Lancet diet proposed in 2019, a healthy and sustainable diet proposal (1, 2). The PHDI can range from 0 to 140 and considers 15 food groups, which can be mainly categorised into two groups:
- Healthy food with low environmental footprints: whole grains, non-starchy vegetables, whole fruits, fish and shellfish, nuts, non-soy legumes (such as peas and lentils), soy foods, and added unsaturated fats.
- Food products labelled as ‘unhealthy’ and/or less environmentally friendly: tubers (potatoes, cassava), red and processed meat, dairy, chicken and poultry, eggs, added saturated fats, and added sugars. The higher the consumption of these, the lower the score.
Key results from the study
After controlling for the effects of age and multiple demographic and lifestyle variables, a higher PHDI was associated with lower mortality: participants in the highest category of PHDI had a 23% reduced risk of death, in comparison to those who were in the lowest category.
In addition, the highest category of PHDI presented 29% lower greenhouse emissions, 21% reduction in fertilizer, and 51% lower cropland use than the lowest category, confirming its significant environmental benefits.
Addressing Food Loss and Waste
Incorporating food loss and waste into the conversation around PHDI is critical, as these factors significantly impact both environmental sustainability and food security. According to the Food and Agriculture Organization (FAO), approximately one-third of all food produced for human consumption is lost or wasted each year, contributing to unnecessary greenhouse gas emissions and resource depletion. By adopting a high PHDI, individuals can not only choose foods that are healthier for them but also engage in practices that reduce food waste—such as meal planning, portion control, and creative uses for leftovers—thereby amplifying the positive effects on both personal health and the environment.
Next steps
This study provides robust evidence about the associations between high PHDI and both lower mortality and lower environmental impact. While these results are promising for human and planetary health, it is important to note that the diet assessment in this study was based on self-reported data, which can be imperfect. As strengths, researchers analysed a large sample, with appropriate statistical methods, follow-up time, and sensitivity analyses. However, we still need more research with long-term follow-up across diverse populations and ethnic groups with different diets, to provide more comprehensive evidence on these associations.
In the meantime, adopting a diet high in PHDI may provide us with benefits both for our health and for the environment. Effective communication to promote the understanding of how food groups contribute to the score differently would be key, as well as acceptance from the population. Moving forward, increased awareness of how our food choices may impact both our longevity and the environment may lead to more sustainable and healthier diets.
References
1. Bui LP, Pham TT, Wang F, Chai B, Sun Q, Hu FB, et al. Planetary Health Diet Index and risk of total and cause-specific mortality in three prospective cohorts. The American Journal of Clinical Nutrition. 2024;120(1):80-91. https://www.sciencedirect.com/science/article/pii/S0002916524003897?via%3Dihub
2. The EAT-Lancet Commission, Healthy Diets from Sustainable Food systems: Food Planet Health. Available from: https://eatforum.org/content/uploads/2019/07/EAT-Lancet_Commission_Summary_Report.pdf.
Article by Josefina Orliacq MSc, MD.
