Highlight
- Higher adherence to the Planetary Health Diet Index (PHDI) significantly lowers the risk of developing type 2 diabetes.
- The PHDI’s protective effect is comparable or superior to several well-established plant-based diet scores, including the alternate Mediterranean Diet and DASH.
- Vegetables, fish, reduced red/processed meats, and limited added sugars consumption drive reduced diabetes risk within these dietary patterns.
- Body mass index (BMI) partially mediates but does not fully explain the relationship between PHDI adherence and diabetes risk.
Study Background
Type 2 diabetes mellitus (T2DM) remains a major contributor to global morbidity and mortality, characterized by insulin resistance and pancreatic beta-cell dysfunction leading to chronic hyperglycemia. The rising prevalence parallels lifestyle factors including diet quality, obesity, and sedentary behavior. Plant-based diets (PBDs), emphasizing whole plant foods and minimizing animal products, have garnered attention for their role in metabolic health and chronic disease prevention. Such diets also carry environmental sustainability benefits, aligning with planetary health goals.
The Planetary Health Diet Index (PHDI) operationalizes adherence to a diet designed for both human health and ecological sustainability, incorporating 14 food groups with specific consumption recommendations. Despite the theoretical advantages, epidemiologic evidence linking PHDI adherence to T2DM risk remains sparse, especially in large-scale prospective cohorts. The current study addresses this gap by evaluating the PHDI alongside other recognized PBDs such as the alternate Mediterranean Diet (aMED), healthful plant-based diet index (hPDI), Dietary Approaches to Stop Hypertension (DASH), and Alternate Healthy Eating Index (AHEI-2010).
Study Design
This prospective cohort study utilized data from 112,032 middle-aged adults (40-69 years) from the UK Biobank, all free of T2DM and cardiovascular disease at baseline (2009–2012). Dietary intake was assessed using at least two 24-hour dietary recalls per participant, capturing detailed food consumption.
Foods were categorized to compute PHDI scores (scale 0 to 130), reflecting adherence to the Planetary Health Diet recommendations across 14 food groups. Comparative diet scores (aMED, hPDI, DASH, AHEI-2010) were calculated using established methodologies.
Incident T2DM was ascertained through linked clinical data, including hospital records and self-reports, over a median 9.4-year follow-up until 2021. Cox proportional hazards regression models estimated hazard ratios (HRs) and 95% confidence intervals (CIs), adjusting for potential confounders such as age, sex, socioeconomic status, smoking, physical activity, and energy intake. BMI was further adjusted to assess its mediating effect.
Key Findings
During follow-up, 2,666 new T2DM cases were identified. Participants with the highest adherence to the PHDI (top quartile) demonstrated a 43% lower risk of developing T2DM compared to those in the lowest adherence quartile (multivariable-adjusted HR 0.57, 95% CI 0.50 to 0.64). This risk reduction was more pronounced than that observed for aMED (HR 0.70, 95% CI 0.62 to 0.78) and hPDI (HR 0.64, 95% CI 0.57 to 0.72), and comparable to DASH (HR 0.58, 95% CI 0.51 to 0.65) and AHEI-2010 (HR 0.59, 95% CI 0.53 to 0.67).
Adjusting for BMI attenuated these hazard ratios by 13-19%, indicating that while adiposity partially mediates the diet-diabetes association, other physiological pathways likely contribute. Key components associated with lower T2DM risk included high intake of vegetables and fish, and limiting red/processed meats and added sugars.
These findings underscore the metabolic benefits of dietary patterns that balance health and sustainability without compromising clinical efficacy when compared to established plant-based diets.
Expert Commentary
The large sample size, prospective design, and robust outcome ascertainment strengthen the reliability of these results. The use of repeated 24-hour dietary recalls enhanced exposure assessment precision, though some measurement error remains inevitable.
The partial attenuation upon BMI adjustment aligns with the established role of obesity as a diabetes risk factor, also suggesting that the PHDI may influence diabetes risk via improved insulin sensitivity, reduced inflammation, or modulation of gut microbiota.
Given the comparability with other validated diet scores, the PHDI offers an attractive framework integrating nutritional and planetary concerns. However, generalizability may be limited to similar middle-aged European populations, and residual confounding cannot be excluded.
Future studies should explore mechanistic pathways and assess intervention feasibility and long-term adherence in diverse settings.
Conclusion
This UK Biobank prospective analysis establishes that higher adherence to the Planetary Health Diet Index is robustly associated with reduced risk of type 2 diabetes, with effect sizes comparable to or greater than other renowned plant-based dietary indices. The results support dietary recommendations that harmonize human metabolic health with environmental sustainability, suggesting that promotion of the PHDI might constitute an effective public health strategy to curb the growing diabetes epidemic.
Further research is warranted to clarify biological mechanisms and to implement sustainable dietary interventions at the population level.
