BACKGROUND: Plant-based diets have been recommended to reduce the risk of type 2 diabetes (T2D). However, not all plant foods are necessarily beneficial. We examined the association of an overall plant-based diet and hypothesized healthful and unhealthful versions of a plant-based diet with T2D incidence in three prospective cohort studies in the US.
METHODS AND FINDINGS: We included 69,949 women from the Nurses' Health Study (1984-2012), 90,239 women from the Nurses' Health Study 2 (1991-2011), and 40,539 men from the Health Professionals Follow-Up Study (1986-2010), free of chronic diseases at baseline. Dietary data were collected every 2-4 y using a semi-quantitative food frequency questionnaire. Using these data, we created an overall plant-based diet index (PDI), where plant foods received positive scores, while animal foods (animal fats, dairy, eggs, fish/seafood, poultry/red meat, miscellaneous animal-based foods) received reverse scores. We also created a healthful plant-based diet index (hPDI), where healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, vegetable oils, tea/coffee) received positive scores, while less healthy plant foods (fruit juices, sweetened beverages, refined grains, potatoes, sweets/desserts) and animal foods received reverse scores. Lastly, we created an unhealthful plant-based diet index (uPDI) by assigning positive scores to less healthy plant foods and reverse scores to healthy plant foods and animal foods. We documented 16,162 incident T2D cases during 4,102,369 person-years of follow-up. In pooled multivariable-adjusted analysis, both PDI and hPDI were inversely associated with T2D (PDI: hazard ratio [HR] for extreme deciles 0.51, 95% CI 0.47-0.55, p trend < 0.001; hPDI: HR for extreme deciles 0.55, 95% CI 0.51-0.59, p trend < 0.001). The association of T2D with PDI was considerably attenuated when we additionally adjusted for body mass index (BMI) categories (HR 0.80, 95% CI 0.74-0.87, p trend < 0.001), while that with hPDI remained largely unchanged (HR 0.66, 95% CI 0.61-0.72, p trend < 0.001). uPDI was positively associated with T2D even after BMI adjustment (HR for extreme deciles 1.16, 95% CI 1.08-1.25, p trend < 0.001). Limitations of the study include self-reported diet assessment, with the possibility of measurement error, and the potential for residual or unmeasured confounding given the observational nature of the study design.
CONCLUSIONS: Our study suggests that plant-based diets, especially when rich in high-quality plant foods, are associated with substantially lower risk of developing T2D. This supports current recommendations to shift to diets rich in healthy plant foods, with lower intake of less healthy plant and animal foods.
Our study suggests that plant-based diets, especially when rich in high-quality plant foods, are associated with substantially lower risk of developing T2D.
large prospective observational cohorts support the association, but residual confounding prevents causal identification
uPDI was positively associated with T2D even after BMI adjustment (HR for extreme deciles 1.16, 95% CI 1.08-1.25, p trend < 0.001)
the adjusted association is consistently reported, but its modest magnitude remains susceptible to residual confounding in an observational design
The association of T2D with PDI was considerably attenuated when we additionally adjusted for body mass index (BMI) categories (HR 0.80, 95% CI 0.74-0.87, p trend < 0.001)
observational adjustment documents attenuation but cannot resolve BMI's confounding-versus-mediation role
Our study supports current recommendations to shift to diets rich in healthy plant foods, with lower intake of less healthy plant and animal foods.
recommendation support is corroborative because the observational design does not establish benefits from changing diet
These associations were independent of BMI and other diabetes risk factors.
BMI-adjusted observational associations do not establish broader independence from adiposity or unmeasured risk factors
Derived from the full evaluation — not a separate score.
Strengths
Separate healthful and unhealthful indices reveal opposing associations with diabetes incidence, adding information beyond a simple plant-versus-animal or vegetarian distinction.
↳ Introduction; Methods, Plant-Based Diet Indices; Results, Plant-Based Diet Indices and Type 2 Diabetes Incidence
The analysis includes 200,727 participants and 16,162 incident cases, with repeated dietary assessment and a validated supplementary questionnaire for diabetes confirmation.
↳ Methods, Study Population, Dietary Assessment, and Ascertainment of Type 2 Diabetes
Baseline-only and most-recent diet analyses, a glucose-screened restriction, additional socioeconomic adjustment, and adjustment for other dietary patterns preserve the principal inverse associations.
↳ Results, Sensitivity Analyses
Limitations
Extensive measured adjustment cannot establish that changing the dietary indices would itself prevent diabetes. BMI may also represent both confounding and mediation, complicating interpretation of adjusted magnitudes.
↳ Methods, Statistical Analysis; Discussion, BMI interpretation and limitations
Response rates and baseline exclusions are reported, but selection associated with incomplete dietary data, missingness, and differential follow-up is not analytically characterised.
↳ Methods, Study Population and Statistical Analysis
The BMI-adjusted hPDI estimate is pooled using fixed effects despite significant between-cohort heterogeneity. The Discussion's blanket BMI-independence wording also obscures the distinction between a surviving adjusted association and an unchanged association.
↳ Results, Plant-Based Diet Indices and Type 2 Diabetes Incidence; Discussion, first paragraph
The graded indices and the contrast between healthful and unhealthful plant-based patterns provide the main conceptual contribution. Repeated dietary measurements, confirmed diabetes ascertainment, and extensive sensitivity analyses support the longitudinal associations. Selection and missingness are less fully examined, and significant hPDI heterogeneity warrants more caution around the pooled estimate. The findings can inform existing dietary guidance, but neither large cohort size nor validated questionnaires establish that index-guided dietary change prevents diabetes.
Nabu’s assessment, alongside the field’s view.
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Strong3.8
Confidence highGraded overall, healthful, and unhealthful indices distinguish plant-food quality beyond prior vegetarian/nonvegetarian comparisons. The advance remains an observational extension of existing dietary-pattern evidence.
Repeated prospective diet measurement, confirmed outcomes, broad covariate adjustment, and sensitivity analyses support the principal associations. Selection and missingness are incompletely examined, with additional uncertainty from BMI interpretation and fixed-effects pooling despite heterogeneity.
The progression from index construction to association-based conclusions is followable, and the abstract supplies the relevant estimates. Blanket BMI-independence language and optimistic generalisability wording reduce precision without obscuring the reported results.
The paper engages its closest dietary-pattern antecedents and acknowledges measurement error, residual confounding, and population restrictions. Heterogeneity and the implications of residual confounding receive less interpretive attention than the pooled recommendation-supporting conclusion.
Lower confidence on Methodological Rigour, Positioning — domain match limited.
No concerns4 of 4 checks
The reported numbers and statistics are consistent with the stated results.
Institutional review-board approval and implied consent are declared. Statements unavailable in the supplied extract are treated as unknown rather than as reporting failures.
Ethics approval: declared
56 references in manuscript 53 of 54 checkable references found in an index 2 are books, websites or datasets — counted, but not index-checkable
References not verified automatically are resolved manually within 24 hours.
No retraction or expression of concern found in Crossref (includes Retraction Watch).
Sources: Crossref (incl. Retraction Watch) ✓
Where this paper’s evidence sits on the path from initial observation to real-world use.
The results can corroborate recommendations about plant-food quality in free-living adults. No intervention or implementation evaluation establishes the effectiveness of index-guided counselling.
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