Low fibre intake has emerged as a risk factor for the development of high blood pressure, a condition that affects over a billion people globally and is the leading contributor to cardiovascular disease. However, the biological pathways and specific metabolites involved remain unclear. This Thesis investigates how a lack of dietary fibre modulates the gut microbiome, impacting the host plasma metabolome in experimental and clinical hypertension. Findings reveal that under fibre-deprived conditions, the gut microbiota shifts its resource preference, fermenting tyrosine into p-Cresol, which increases p-Cresol glucuronide and p-Cresol sulfate in host circulation, potentially contributing to elevated blood pressure.