Cardiometabolic disease (CMD) was a major contributor to the leading cause of global mortality in 2022, counting towards 19.8 million deaths, with prevalence steadily increasing(1). There is a strong push by international bodies to adopt plant-based protein sources into mainstream diets to enhance sustainability and longevity(2). Previous research has focussed on protein intake from either plant or animal sources separately. However, exploration into the balance of animal-to-plant protein within the diet and its association with CMD has been extremely limited. This study will investigate if protein amount, source (animal & plant) and animal-to-plant protein ratio (A:P) is associated with CMD risk factors (triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, glucose, high sensitivity C-reactive protein, blood pressure, waist circumference, body mass index) in those aged ≥40 years. This is a secondary cross-sectional analysis of UK Biobank (n = >500,000) (3). From 2009, participants aged 40-69 years attended one of 22 clinics located throughout the UK for baseline assessment, completing computerised questionnaires, physical measurements and blood sampling. A 24-hr dietary questionnaire (Oxford WebQ) assessed protein source and amount (g/day). A:P was calculated by dividing total grams per day of animal protein by total grams per day of plant protein. Biochemical assays were conducted for serum glucose, triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), high sensitivity C-reactive protein. Waist circumference (WC) was measured at the smallest part of the trunk (SECA). Body mass index (BMI) was calculated as weight (kg) divided by height (m2). Two automated blood pressure measures were recorded and mean analysed. After exclusions, n = 22,605 with complete data were included. The mean age of participants was 55.6 ± 8.19 years with 55.7% females. Mean total protein was 80.8g/.day, with mean animal protein reported as 51.9g/day, whereas mean plant protein intake was 28.9g/day. Mean A:P of 2.25 indicates the population consumed higher proportions of animal protein than plant protein. There were significant associations between higher A:P and higher BMI (B = 0.007, p = 0.012) and WC (B = 0.03, p = 0.003). Further multiple linear regression analysis will be used to investigate associations between protein intake exposures and cardiometabolic risk factors, controlling for confounders identified by Directed Acyclic Graphs. The findings of this study will reveal critical associations into the under-researched area of protein intake and health in middle- and older-age. It will lay a foundation for further research into nutritional interventions for cardiometabolic disease prevention and inform identification of an optimal A:P range. This can be applied to dietary recommendations and practice, to enhance both individual and population CMD outcomes. Dietary guidelines can utilise this information to tailor recommendations of animal and plant protein to different population groups.