Postprandial oxidative stress is characterized by an increased susceptibility of the organism towards oxidative damage after consumption of a meal rich in lipids and/or carbohydrates. We have investigated whether the quality of dietary fat alters postprandial gene expression and protein levels involved in oxidative stress and whether the supplementation with coenzyme Q(10) (CoQ) improves this situation in an elderly population. Twenty participants were randomized to receive three isocaloric diets each for 4 weeks: Mediterranean diet supplemented with CoQ (Med + CoQ diet), Mediterranean diet (Med diet), saturated fatty acid-rich diet (SFA diet). After 12-h fast, volunteers consumed a breakfast with a fat composition similar to that consumed in each of the diets. Nrf2, p22(phox) and p47(phox), superoxide dismutase 1 and 2 (SOD1 and SOD2), glutathione peroxidase 1 (GPx1), thiorredoxin reductase (TrxR) gene expression and Kelch-like ECH associating protein 1 (Keap-1) and citoplasmic and nuclear Nrf2 protein levels were determined. Med and Med + CoQ diets induced lower Nrf2, p22(phox), p47(phox), SOD1, SOD2 and TrxR gene expression and higher cytoplasmic Nrf2 and Keap-1 protein levels compared to the SFA diet. Moreover, Med + CoQ diet produced lower postprandial Nrf2 gene expression and lower nuclear Nrf2 protein levels compared to the other diets and lower GPx1 gene expression than the SFA diet. Our results support the antioxidant effect of a Med diet and that exogenous CoQ supplementation has a protective effects against free radical overgeneration through the lowering of postprandial oxidative stress modifying the postprandial antioxidant protein levels and reducing the postprandial expression of antioxidant genes in peripheral blood mononuclear cells.