Abstract
Background: Plant-based diets, often referred to as vegetarian diets, are associated with health benefits. However, the association with mortality is less clear. Objective: We investigated associations between plant-based diet indexes and all-cause and cardiovascular disease mortality in a nationally representative sample of US adults. Methods: Analyses were based on 11,879 participants (20-80 y of age) from NHANES III (1988-1994) linked to data on all-cause and cardiovascular disease mortality through 2011. We constructed an overall plant-based diet index (PDI), which assigns positive scores for plant foods and negative scores for animal foods, on the basis of a food-frequency questionnaire administered at baseline. We also constructed a healthful PDI (hPDI), in which only healthy plant foods received positive scores, and a less-healthful (unhealthy) PDI (uPDI), in which only less-healthful plant foods received positive scores. Cox proportional hazards models were used to estimate the association between plant-based diet consumption in 1988-1994 and subsequent mortality. We tested for effect modification by sex. Results: In the overall sample, PDI and uPDI were not associated with all-cause or cardiovascular disease mortality after controlling for demographic characteristics, socioeconomic factors, and health behaviors. However, among those with an hPDI score above the median, a 10-unit increase in hPDI was associated with a 5% lower risk in all-cause mortality in the overall study population (HR: 0.95; 95% CI: 0.91, 0.98) and among women (HR: 0.94; 95% CI: 0.88, 0.99), but not among men (HR: 0.95; 95% CI: 0.90, 1.01). There was no effect modification by sex (P-interaction > 0.10). Conclusions: A nonlinear association between hPDI and all-cause mortality was observed. Healthy plant-based diet scores above the median were associated with a lower risk of all-cause mortality in US adults. Future research exploring the impact of quality of plant-based diets on long-term health outcomes is necessary. J Nutr 2018;148:624-631.
Generated Summary
This research article, published in “The Journal of Nutrition”, investigates the association between plant-based diet indexes and all-cause and cardiovascular disease mortality in a nationally representative sample of US adults. The study analyzed data from the NHANES III survey (1988-1994), linking it to mortality data through 2011. The primary goal was to determine if different plant-based diet indexes (overall plant-based diet index (PDI), healthy plant-based diet index (hPDI), and less-healthy plant-based diet index (uPDI)) were associated with mortality. The research employed Cox proportional hazards models to estimate associations between plant-based diet consumption and subsequent mortality, also testing for effect modification by sex. The study aimed to address the limitations of previous research by using a large, diverse sample and examining the impact of the quality of plant-based diets, considering healthy and less-healthy plant-based food consumption. The study’s methodology involved a multi-stage, stratified, clustered probability sampling approach to provide a nationally representative estimate of the noninstitutionalized civilian population in the United States. Participants were categorized based on their PDI, hPDI, and uPDI scores derived from a food frequency questionnaire. The study considered potential confounders such as demographic characteristics, socioeconomic factors, and health behaviors in their analyses.
Key Findings & Statistics
- The study analyzed data from 11,879 participants.
- Over a median follow-up of 19 years, 2228 deaths occurred, with 543 from cardiovascular diseases.
- The PDI ranged from 24 to 75 (median: 49; 10th-90th percentile range: 43-58), the hPDI ranged from 28 to 78 (median: 51; 10th-90th percentile range: 43-60), and the uPDI ranged from 31 to 78 (median: 52; 10th-90th percentile range: 44-61).
- In the overall sample, a 10-unit increase in hPDI was associated with a 5% lower risk in all-cause mortality (HR: 0.95; 95% CI: 0.91, 0.98) in the overall study population.
- A 10-unit increase in hPDI was associated with a lower risk of all-cause mortality among those with hPDI scores above the median.
- The PDI and uPDI were not associated with all-cause or cardiovascular disease mortality in the overall sample.
- The PDI and uPDI were not associated with the risk of death among men or women.
- No significant effect modification by sex was observed on the association between the PDI (P-interaction = 0.16), hPDI (P-interaction = 0.11), or uPDI (P-interaction = 0.55) and all-cause mortality.
- Neither the PDI, hPDI, nor uPDI was associated with deaths from cardiovascular diseases.
- Participants with a higher PDI score were more likely to be women, non-Hispanic white, older, and married; more likely to have higher levels of education; less likely to smoke; and more likely to be physically active.
- Participants in the highest decile of PDI and hPDI consumed greater amounts of fiber, vitamin C, and folate and lower amounts of dietary cholesterol, sodium, saturated fat, and monounsaturated fat as a percentage of energy.
Other Important Findings
- The study found that a 10-unit increase in hPDI was associated with a lower risk of all-cause mortality among women but not among men.
- There was a nonlinear association between hPDI and all-cause mortality.
- Healthy plant-based diet scores above the median were associated with a lower risk of all-cause mortality in US adults.
- The hPDI above the median was associated with a lower risk of death from all causes in women.
- No significant association was observed for men.
- There was no significant effect modification by sex or age.
Limitations Noted in the Document
- The study relied on self-reported dietary intake, which is subject to reporting error.
- The NHANES III used a food frequency questionnaire (FFQ) without a validation study.
- Diet was assessed only at baseline, and repeated assessments of dietary intake were not available.
- The duration of time consuming plant-based diets was not available in the study.
- The possibility of residual confounding remains due to unmeasured covariates or errors in the measured confounding factors.
- The results may be overadjusted and underestimate the true association between plant-based diets and mortality.
Conclusion
The study’s findings suggest that a healthy plant-based diet, particularly for women, is associated with a lower risk of all-cause mortality. The research emphasizes the importance of the quality of plant-based diets, distinguishing between healthy and less-healthy plant foods. The study’s nuanced approach, using an hPDI, showed that the benefits of a plant-based diet are most evident in those with higher adherence to healthy plant-based eating patterns. The authors highlight the need for future research to explore the impact of the quality of plant-based diets on long-term health outcomes. The study’s results build upon previous research that has shown benefits of plant-based diets, the current study contributes to the existing body of knowledge by examining the relationship between plant-based diets and mortality, while also accounting for the differences in the quality of plant-based diets. The study recognizes that previous research has sometimes oversimplified the classification of diets. The study’s focus on the quality of plant-based diets provides a more comprehensive understanding of their effects on mortality. The sex-specific findings indicate the complexity of dietary patterns and their effects. The study calls for more research on the long-term health effects of plant-based diets. The authors suggest that future research should consider the consumption of less-healthy plant foods, in addition to the benefits of healthy plant-based diets. Further research is needed to confirm these findings and to explore the optimal amounts of consumption of foods. The study also emphasizes the need for a nuanced approach in studying dietary patterns and their effects on health outcomes. The study’s results provide additional information for dietary guidelines.