Greater adherence to an overall plant-based diet, and more healthful plant-based diet, is associated with fewer depressive symptoms and greater well-being among middle- to older-aged adults.
Key Findings
Results
The overall PDI (oPDI) and healthy PDI (hPDI) were negatively associated with depressive symptoms in age and sex-adjusted models.
Anxiety was assessed using the anxiety sub-scale of the Hospital Anxiety and Depression Scale (HADS)
This association with anxiety persisted upon full adjustment for potential confounders
Methods
The study was a cross-sectional analysis of 1,949 middle- to older-aged men and women from the Mitchelstown Cohort.
Sample size: n = 1,949 participants
Population described as middle- to older-aged men and women
PDIs were calculated from validated food frequency questionnaires
Three PDI measures were examined: overall PDI (oPDI), healthy PDI (hPDI), and unhealthy PDI (uPDI)
Regression analyses investigated PDI relationships with mental health scores adjusted for potential confounders
Background
Plant-based dietary indices have been previously linked with favourable cardiometabolic health outcomes, but investigation of PDI associations with mental health outcomes has been limited.
The study addresses a gap in the literature by examining PDI associations with depressive symptoms, anxiety, and well-being
Three mental health outcomes were assessed: depressive symptoms (CES-D), anxiety (HADS anxiety sub-scale), and well-being (WHO-5)
Future longitudinal studies exploring causal relationships between PDIs and psychological outcomes are identified as warranted
What This Means
This research suggests that people who follow plant-based diets more closely — particularly healthier versions of plant-based diets — tend to report fewer symptoms of depression and greater overall well-being. The study examined nearly 2,000 middle- to older-aged adults in Ireland and used established questionnaires to measure how closely participants followed plant-based dietary patterns, as well as standardized tools to assess their mental health. Those with higher scores on both an overall plant-based diet index and a 'healthy' plant-based diet index reported fewer depressive symptoms and higher well-being scores, and the overall plant-based diet index was also linked to lower anxiety.
Importantly, these associations held up even after the researchers accounted for other factors that could explain the relationships, and a dose-response pattern was observed for depression — meaning that as plant-based diet adherence increased across groups, depressive symptom scores tended to decrease in a stepwise fashion. This adds weight to the finding beyond a simple correlation. The unhealthy plant-based diet index, which captures plant-based eating that relies on less nutritious plant foods, was not highlighted as showing the same beneficial associations, suggesting that the quality of plant-based food choices matters.
This research suggests a potential link between diet quality — specifically healthful plant-based eating — and mental health in mid-to-later life. However, because this was a cross-sectional study (a snapshot in time), it cannot determine whether eating a plant-based diet causes better mental health, or whether people with better mental health are more likely to adopt such diets. The authors call for future studies that follow people over time to better understand whether and how plant-based diets might causally influence psychological well-being.
Millar S, Perry I, Phillips C. (2026). Plant-based dietary indices and mental health: a cross-sectional study of a middle- to older-aged population.. European journal of nutrition. https://doi.org/10.1007/s00394-026-04000-z