Suboptimal diets are among the leading factors fuelling the global rise in the prevalence of type 2 diabetes and other metabolic disorders. Most epidemiological studies of the associations between diet and nutritional factors and metabolic outcomes have relied on self-report instruments. Nutritional biomarkers offer a complementary objective approach but have not been widely applied in African settings to test associations between diet and metabolic outcomes. This thesis aimed to examine the relationship between diet and nutritional factors assessed using a wide range of objectively measured nutritional biomarkers and metabolic outcomes in a population-based study in adults in rural and urban Cameroon (n= 651). I spent the first part of my PhD in the laboratory measuring circulating vitamin D, folate, holotranscobalamin, carotenoids and tocopherol using mass spectrometry techniques. Subsequently, I undertook analyses to describe the patterns and identify factors affecting these nutritional biomarkers reflecting dietary intakes and plasma zinc, which was measured in an external laboratory. Most of the biomarkers showed distinct patterns by age, sex, level of education, physical activity levels and rural/urban area of residence. I then investigated the independent cross-sectional associations of these biomarkers with metabolic risk factors exploring the possibility of both linear and non-linear associations and adjusting for a wide range of potential confounders. Circulating folate and carotenoids, which are associated with intake of fruits and vegetables, showed an inverse association with the metabolic syndrome score and fasting glucose respectively. Holotranscobalamin, a biomarker that reflects intake of animal-sourced foods, was positively associated with the metabolic syndrome score. Circulating zinc, reflecting intake of protein-rich foods, was inversely associated with several markers of glucose homeostasis (fasting and 2-h glucose and homeostatic model assessment for insulin resistance). Higher 25-hydroxy-vitamin D, a marker of vitamin D status, was associated with lower fasting glucose. Finally, I investigated the potential effect modification by rural/urban area of residence, sex and body mass index on the association between the biomarker and metabolic outcomes. Overall this PhD showed 1) Rural and urban differences in the distribution of the nutritional biomarkers in Cameroon 2) Significant associations of the studied biomarkers reflecting dietary intakes with metabolic risk factors. Findings from my PhD advance the understanding of the role of diet and nutritional factors on metabolic health in adults in Cameroon. Diet is modifiable, making it a realistic target for public health intervention to improve metabolic health in this population.