Comparative Analysis of Plant-Based Diets vs. Omnivorous Diets on Lipid Profiles

Thesis Abstract

Chronic disease burden linked to dyslipidemia necessitates robust evidence on dietary patterns that modulate lipid profiles across diverse populations. This study investigates how plant-based versus omnivorous diets influence plasma lipid parameters, addressing gaps in the causal understanding of dietary patterns on cardiovascular risk biomarkers. The aim is to determine differences in total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) between adults adhering to plant-based diets and those following omnivorous diets, while adjusting for confounders. Specific objectives include (i) comparing mean lipid values between diet groups; (ii) assessing dose–response relationships with plant-based dietary indices; (iii) evaluating the mediating role of body mass index (BMI), physical activity, and dietary fat quality (saturated fat, monounsaturated fat, polyunsaturated fat) on lipid outcomes; and (iv) exploring potential effect modification by age and sex. A cross-sectional, multi-center design will be employed. The population consists of adults aged 25–65 years recruited from urban and suburban nutrition clinics and community centers in three metropolitan regions. A target sample of 1,200 participants will be stratified into two groups 600 adherents to plant-based diets (including vegetarians and vegans) and 600 omnivores, with dietary adherence verified by a validated food frequency questionnaire (FFQ) and 7-day dietary recalls. Data collection will involve venous blood sampling after an overnight fast to measure TC, LDL-C, HDL-C, and TG using standardized enzymatic assays. Anthropometrics will be measured, and validated questionnaires will capture demographic information, physical activity (accelerometry for a 7-day period and the International Physical Activity Questionnaire), smoking status, alcohol use, and medical history. Additionally, a 24-hour dietary recall will be used to quantify fat quality indices. Statistical analyses will be conducted using SPSS and R. Descriptive statistics will summarize baseline characteristics. Multivariable linear regression models will compare lipid outcomes between diet groups, adjusting for age, sex, BMI, physical activity, smoking, alcohol intake, total energy intake, and dietary fat quality. Propensity score weighting will be applied to mitigate selection bias inherent in observational designs. Mediation analyses will examine indirect effects of BMI and fat quality on the diet–lipid associations, while interaction terms will test effect modification by age and sex. Sensitivity analyses will exclude individuals with pre-existing dyslipidemia or lipid-lowering therapy. The study anticipates that plant-based diet adherents will exhibit significantly lower LDL-C and TG and higher HDL-C compared with omnivores, with smaller effect sizes for TC depending on fat quality and adherence level. The magnitude of lipid differences is expected to correlate with plant-based dietary indices (e.g., higher fiber, lower saturated fat, and greater intake of polyunsaturated fats). The theoretical framework will integrate the Diet-Disease Causality paradigm and the Theory of Nutritional Ecology to interpret how macronutrient composition and dietary patterns influence lipid metabolism, while considering behavioral determinants of dietary choice. The findings will contribute to knowledge by clarifying the lipid-modulating potential of plant-based diets in diverse adult populations, identifying mediators and modifiers that inform personalized dietary guidance, and informing public health strategies for cardiovascular risk reduction. Practical implications include evidence-based recommendations for clinicians and dietitians regarding diet prescriptions for dyslipidemia management, and guidance for public health messaging that emphasizes fat quality and dietary patterns over macronutrient elimination alone. The study's limitations, including cross-sectional design and potential residual confounding, will be acknowledged, with suggestions for longitudinal and intervention-based research to confirm causal pathways. The conclusion will emphasize that adopting plant-based dietary patterns, when combined with favorable fat quality and lifestyle factors, may offer meaningful improvements in lipid profiles and cardiovascular risk reduction, warranting integration into dietary guidelines and individualized patient care.