Using the plant-based diet index to measure disease risk

Aim

The plant-based diet index (PDI) was developed to evaluate the healthfulness of a person’s diet.

Using food frequency questionnaires, plant-based foods are scored positively, and animal foods are scored inversely.

The plant-based diet index differentiates the healthfulness of a diet by using three categories: overall PDI, healthful (hPDI), and unhealthful (uPDI).

The reliability of the PDI has been previously established, and it has been utilised in a variety of studies.

The aim of this narrative review was to give an overview of the PDI, how it relates to health outcomes, its strengths, weaknesses and to give recommendations for its use in future research.

Method

The authors searched PubMed for papers between 2016 (when the PDI tool was originally developed) and 2023. Criteria included using the PDI to evaluate high prevalence health outcomes in adults. Study designs were cross-sectional, prospective case-control, and cohort studies.

Key findings

61 studies were summarised in this review.

Identified publications primarily focused on metabolic and cardiovascular health (49 papers) and touched on microbiome and cognitive impairment and wellbeing (12 articles). Papers from 23 different countries were included and participant age ranged from 36 to 81 years.

Study outcomes revealed adherence to a healthier plant-based diet was associated with lower risk of metabolic factors including hypertension (17-35% lower risk), obesity (25% lower risk), and dyslipidaemia (37% lower risk).

Studies that examined type 2 diabetes mellitus (T2D) using PDI showed both PDI and hPDI were linked to a lower risk of developing T2D, with a 14-46% lower risk for those with a higher hPDI score. Insulin sensitivity increased by 10% with each 10-unit increase in hPDI.

When highest and lowest hPDI adherence were compared, higher hPDI adherence was associated with an 8-68% decreased risk of cardiovascular disease (CVD), 10% decreased for stroke, and 17-25% decreased for coronary heart disease. In contrast, adherence to an uPDI related an increase in risk of 21% for CVD and 32% increased risk for coronary heart disease. Higher adherence to hPDI was associated with 9-36% lower risk of CVD mortality.

A healthier plant-based diet has a decreased risk of all-cause mortality (10-36%), whereas an unhealthy plant-based diet may have the opposite effect.

Adherence to hPDI was associated with slower cognitive decline and increased mental and physical wellbeing.

hPDI demonstrated enhanced microbiome species abundance and diversity, but uPDI showed the reverse impact.

Conclusion

The authors outline the PDI tool's strengths as its versatility and capacity to be employed across varied demographics. Overall, they conclude that the PDI is an effective tool for assessing plant-based diet adherence and presenting research on plant-based diets and health.

For future research using the PDI tool, the authors advocate (1) giving detailed descriptions of any deviations from the original scoring pattern, (2) how these deviations may affect results, (3) providing intake overviews, (4) adjusting food item categorisation relevant to the study population, and (5) assessing relationships across age groups.

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