Consumption of industrially produced trans fatty acids (IP-TFA) has been positively associated to systemic markers of low-grade inflammation and endothelial dysfunction in cross-sectional studies, but results from intervention studies are inconclusive. Therefore, we conducted a 16-week double-blind parallel intervention study with the objective to examine the effect of IP-TFA intake on biomarkers of inflammation, oxidative stress and endothelial dysfunction. Fifty-two healthy overweight postmenopausal women (49 completers) were randomized to receive either partially hydrogenated soybean oil (15.7 g/day IP-TFA) or control oil without IP-TFA. After 16 weeks, IP-TFA intake increased baseline-adjusted serum tumor necrosis factor (TNF)α by 12% (95% confidence interval (CI): 5-20; P=0.002) more in the IP-TFA group compared to controls. Plasma soluble TNF receptors 1 and 2 were also increased by IP-TFA [155 pg/ml (CI: 63-247); P<0.001 and 480 pg/ml (CI: 72-887); P=0.02, respectively]. Serum C-reactive protein, interleukin (IL) 6 and adiponectin and subcutaneous abdominal adipose tissue mRNA expression of IL6, IL8, TNFα and adiponectin as well as ceramide content were not affected by IP-TFA, neither was urinary 8-iso-prostaglandin-F2α. In conclusion, this dietary trial indicates that the mechanisms linking dietary IP-TFA to cardiovascular disease may involve activation of the TNFα system.