Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults

Abstract

Background: Plant-based diets are recommended for coronary heart disease (CHD) prevention. However, not all plant foods are necessarily beneficial for health.

Objectives: This study sought to examine associations between plant-based diet indices and CHD incidence.

Methods: We included 73,710 women in NHS (Nurses' Health Study) (1984 to 2012), 92,329 women in NHS2 (1991 to 2013), and 43,259 men in Health Professionals Follow-up Study (1986 to 2012), free of chronic diseases at baseline. We created an overall plant-based diet index (PDI) from repeated semiquantitative food-frequency questionnaire data, by assigning positive scores to plant foods and reverse scores to animal foods. We also created a healthful plant-based diet index (hPDI) where healthy plant foods (whole grains, fruits/vegetables, nuts/legumes, oils, tea/coffee) received positive scores, whereas less-healthy plant foods (juices/sweetened beverages, refined grains, potatoes/fries, sweets) and animal foods received reverse scores. To create an unhealthful PDI (uPDI), we gave positive scores to less-healthy plant foods and reverse scores to animal and healthy plant foods.

Results: Over 4,833,042 person-years of follow-up, we documented 8,631 incident CHD cases. In pooled multivariable analysis, higher adherence to PDI was independently inversely associated with CHD (hazard ratio [HR] comparing extreme deciles: 0.92; 95% confidence interval [CI]: 0.83 to 1.01; p trend = 0.003). This inverse association was stronger for hDPI (HR: 0.75; 95% CI: 0.68 to 0.83; p trend <0.001). Conversely, uPDI was positively associated with CHD (HR: 1.32; 95% CI: 1.20 to 1.46; p trend <0.001).

Conclusions: Higher intake of a plant-based diet index rich in healthier plant foods is associated with substantially lower CHD risk, whereas a plant-based diet index that emphasizes less-healthy plant foods is associated with higher CHD risk.

Keywords: coronary heart disease; diet; dietary pattern; epidemiology; nutrition; prospective cohort study.

Figure 1. Pooled HRs (95% CI) for CHD comparing extreme deciles of the plant-based diet indices, stratified by selected characteristics

The HRs and P values for men and women were obtained after combining all three cohorts. All other HRs and P values were obtained by pooling estimates from the three cohorts using a fixed-effects model. Adjusted for age, smoking status, physical activity, alcohol intake, multivitamin use, aspirin use, family history of CHD, margarine intake, energy intake, baseline hypertension, hypercholesterolemia, and diabetes, and updated body mass index. Also adjusted for postmenopausal hormone use in NHS & NHS2, and for oral contraceptive use in NHS2. Abbreviations: BMI, Body Mass Index; CHD, Coronary Heart Disease; hPDI, Healthful Plant-based Diet Index; MET, Metabolic Equivalent Task; uPDI, Unhealthful Plant-based Diet Index

Central Illustration. Dose-response relationship of (A) the Plant-based Diet Indices and (B) animal, healthy plant, and less healthy plant foods with CHD incidence

Analysis carried out after combining all three cohorts Adjusted for age, smoking status, physical activity, alcohol intake, multivitamin use, aspirin use, family history of CHD, margarine intake, baseline hypertension, hypercholesterolemia, and diabetes, and updated body mass index. Also adjusted for postmenopausal hormone use in NHS & NHS2, and for oral contraceptive use in NHS2. Energy intake was additionally adjusted when analyzing the plant-based diet indices. The three plant-based diet indices were examined in separate models. The three food categories (healthy and less healthy plant foods, and animal foods) were simultaneously included in the same model. For uPDI, p for test of curvature=0.01 and p for non-linear association<0.001. P for test of curvature for PDI=0.25, for hPDI=0.82, for animal foods=0.58, for healthy plant foods=0.99, and for less healthy plant foods=0.74; P for linearity=0.004 for animal foods, 0.001 for PDI, and <0.001 for hPDI, less healthy plant foods, and healthy plant foods. Abbreviations: CHD, Coronary Heart Disease; hPDI, Healthful Plant-based Diet Index; PDI, Overall Plant-based Diet Index; uPDI, Unhealthful Plant-based Diet Index