Plant-Based Diets and Risk of Type 2 Diabetes and Coronary Heart Disease

Abstract

Plant-based diets, defined as “vegetarian” diets, are associated with reduced risk of type 2 diabetes (T2D) and coronary heart disease (CHD). To examine the health effects of gradual reductions in animal food consumption while increasing plant food intake, and to distinguish between healthy and less healthy plant foods, we created three graded plant-based diet indices using semi-quantitative food frequency questionnaires (SFFQ). In the overall plant-based diet index (PDI), all plant foods received positive scores while animal foods received reverse scores. In the healthful PDI (hPDI) healthy plant foods (e.g. whole grains, fruits) received positive scores, while less healthy plant foods (e.g. sweetened beverages, refined grains) and animal foods received reverse scores. In the unhealthful PDI (uPDI) less healthy plant foods received positive scores, while healthy plant foods and animal foods received reverse scores. This dissertation examined the reliability and validity of these diet indices, and evaluated their associations with T2D and CHD incidence. In chapter 1, we used data from The Women’s and Men’s Lifestyle Validation Studies (n=1354) to examine the reliability and validity of SFFQ-assessed plant-based diet indices. We found reasonable one-year reliability for the SFFQ-assessed indices. The indices correlated with energy-adjusted 7-day diet record nutrients and plasma biomarkers in expected directions, with hPDI associated with high dietary quality, and uPDI associated with poor diet quality. In chapters 2 and 3, we examined the associations of these indices with T2D and CHD. We included ~70,000 women from Nurses’ Health Study (NHS) (1984-2012), ~90,000 women from NHS2 (1991-2011), and ~40,000 men from Health Professionals Follow-up Study (1986-2010). Dietary data were collected every 2-4 years using SFFQs. We documented 16,162 incident T2D, and 7754 incident CHD cases during ~4,00,000 person-years of follow-up. In pooled multivariable-adjusted analysis, PDI was inversely associated with T2D and CHD. hPDI had a stronger inverse association with both endpoints, while uPDI was positively associated with both diseases. In conclusion, we found reasonable reliability and validity for three graded plant-based diet indices assessed with SFFQs. Our study suggests that plant-based diets, especially when rich in high-quality plant foods, are associated with substantially lower risk of T2D and CHD.