Plant-based diets and chronic disease risk

: findings from a population-based study

Abstract

Background: Plant-based diets (PBDs) have gained popularity for their favourable effects on human and planetary health, however, the health outcomes associated with PBDs can vary substantially based on diet quality. High-quality PBDs, rich in whole grains, fruits, vegetables, nuts and legumes have been associated with lower disease risk, whereas poor-quality PBDs, high in refined grains, sugary beverages, and processed foods, may not confer the same benefits. The positive effects of healthy PBDs are suggested to be attributed to mechanisms such as body fat regulation, enhanced sugar metabolism, reduced inflammation, and better kidney and liver function, which may largely be due to higher intakes of bioactive compounds, particularly flavonoids.

Aims and Objectives: This thesis aims to explore the role of plant-based dietary patterns, operationalised by diet quality indices (healthful and unhealthful plant-based diet index (hPDI and uPDI) and a flavonoid-rich diet score (FDS)), in relation to the risk of mortality and major chronic diseases using data from the large-scale epidemiological study, the UK Biobank (UKBB). The aims were achieved by addressing five objectives: 1) Implementation of a PDI: Scoring UKBB participants on their healthful and unhealthful PBD consumption using the 24-hr Oxford WebQ dietary assessment and investigating the relationship between the PDIs and the risk of mortality and major chronic disease, specifically cardiovascular disease (CVD), cancer, and fracture (Chapter 2). 2) PDIs and Type 2 Diabetes (T2D) Risk: Investigating the relationship between the PDIs and the risk of T2D in the UKBB and assessing the potential biological mechanisms underlying these associations (Chapter 3). 3) Polyphenol Database Development: Creating polyphenol and flavonoid databases for the UKBB using Phenol-Explorer and U.S Department of Agriculture (USDA) data to estimate intakes. Developing a FDS to investigate the relationship between a flavonoid-rich diet, major food contributors to flavonoid intake, and flavonoid subclasses with T2D risk in the UKBB (Chapter 4). 4) PBD Quality and Chronic Kidney Disease Risk in Diabetes: Examining the associations between PBD quality and chronic kidney disease (CKD) risk among individuals with diabetes and identifying potential underlying biological mechanisms. Additionally, creating an estimated glomerular filtration rate (eGFR) polygenic risk score (PRS) for stratified analyses (Chapter 5). 5) PDIs and Mortality in Chronic Kidney Disease: Investigating the relationship between PDIs and the risk of mortality among patients with chronic kidney disease (CKD) (Chapter 6).

Results: In this large UK-based study, greater adherence to the hPDI was associated with lower risks of mortality, cancer, CVD and T2D, whereas higher adherence to the uPDI was associated with higher risks (Chapter 2 and 3). No significant associations were shown between the PDIs and fracture risk (Chapter 2). Associations between healthful PBDs and T2D risk were partially mediated by lower body fatness and improved kidney and liver function, while unhealthful PBDs were mediated by higher body fatness and elevated triglyceride levels. Among the PDI food groups, higher intakes of vegetables and tea/coffee showed the strongest inverse associations with T2D risk, whereas positive associations were observed for increased consumption of refined grains, potatoes, sugary drinks and meat (Chapter 3). Higher consumption of flavonoids through a flavonoid-rich diet was also inversely associated with incident T2D. These associations were partly mediated by the beneficial effects of flavonoid-rich foods on obesity and sugar metabolism, inflammation, kidney function, and liver health. Red wine, tea, berries and apples were among the flavonoid-rich foods most strongly associated with lower T2D risk (Chapter 4). Among individuals with diabetes, higher intakes of healthy plant foods were associated with lower risks of CKD, whereas higher intakes of unhealthy plant foods were associated with higher risks. These associations were primarily mediated by improved kidney function and lower body fatness. Specifically, tea and coffee consumption was associated with lower CKD risks, while sugar sweetened beverages (SSBs) and meat intake were associated with higher risks (Chapter 5). Among individuals with CKD, greater adherence to a healthy PBD was associated with lower risks of mortality, whereas higher adherence to an unhealthful PBD was associated with higher risks. On a food-group level, higher whole grain intake was associated with lower mortality risks, while higher intakes of refined grains and SSBs were associated with higher risks (Chapter 6).

Conclusions: The present findings support the notion that the quality of PBDs significantly influences health outcomes, with healthful and unhealthful PBDs conferring differential disease risks. A healthful PBD is associated with lower risks of mortality and major chronic diseases, while it may also improve outcomes among those living with chronic disease. Conversely, unhealthful PBDs may pose health risks. These data support the sustained shift toward healthful PBDs for the benefit of both human and planetary health. While the associations between PBD and chronic disease endpoints in the present study were robust upon statistical adjustment, without heterogeneity across subgroups of the population, more randomised controlled trials (RCTs) on the health effects of PBDs under real-world conditions are needed.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Tilman Kuhn (Supervisor) & Aedin Cassidy (Supervisor)