A diet enriched in lupin kernel flour can lower blood pressure, but mechanisms responsible are unclear. Lupin is a source of polyphenols, protein, and L-arginine, factors that may influence blood pressure via effects on oxidative stress and vascular function. Therefore, we aimed to determine the effects of a lupin-enriched diet on oxidative stress and factors influencing vascular function as potential mechanisms for demonstrated benefits on blood pressure. Overweight men and women (n = 88) were recruited to a 16-week parallel-design study. Participants were randomly assigned to replace 15%-20% of their usual daily energy intake with white bread (control) or lupin kernel flour-enriched bread (lupin). All measurements were taken at baseline and 16 weeks. At baseline, plasma F₂-isoprostanes and 20- hydroxyeicosatetraenoic acid (20-HETE) were positively associated with blood pressure, and plasma nitrite was negatively associated with blood pressure (p < 0.05). For lupin relative to control, the estimated differences in plasma F₂-isoprostanes (45 pmol/L; 95%CI: - 68, 158), urinary F ₂-isoprostanes (17 pmol/mmol creatinine; 95%CI: - 43, 76), plasma 20-HETE (75 pmol/L; 95%CI: - 91, 241), and plasma nitrite (-0.3 μmol/L; 95%CI: - 1.1, 0.4) were not significant. Although regular consumption of lupin-enriched bread can lower blood pressure, these results do not support for the hypothesis that this is via effects on oxidative stress or vascular function. © Mary Ann Liebert, Inc.