Overweight persons are at risk for cardiovascular diseases, which may relate to a disturbed endothelial function and pro-inflammatory serum profiles. Indeed, weight loss lowers cardiovascular disease risk, but weight maintenance is difficult. Therefore, dietary supplements such as fish oil, which improve endothelial function, are useful. In this study, we evaluated effects of fish oil and moderate weight loss in the same population. For this, 11 normolipidemic healthy, moderately obese men (BMI 30-35 kg/m2) received in random order 1.1 g/d eicosapentanoic acid (EPA) + docosahexanoic acid (DHA) or oleic acid (control) for 6 wk. In the 3rd period, 8 of the 11 subjects consumed low-energy diets (2 MJ/d) for 4 wk followed by 4 wk weight stabilization. Their body weight was reduced by 9.4 +/- 2.0 kg (P < 0.05). On the final day of all 3 periods, a postprandial test was conducted. Weight loss lowered fasting and postprandial plasma triacylglycerol (TG) responses (P < 0.001), whereas fish oil reduced only postprandial TG (P = 0.006). Fish oil did not affect soluble intercellular adhesion molecule (s-ICAM), whereas weight loss reduced fasting (P = 0.009) and postprandial s-ICAM responses (P < 0.001). Fasting s-ICAM and TG correlated (r = 0.68; P = 0.029), as did changes in fasting s-ICAM and TG during weight loss (r = 0.80; P = 0.029) and fish oil treatment (r = 0.76; P = 0.009). Fasting (P = 0.027) and postprandial (P < 0.001) serum C-reactive protein were lowered by weight loss. The postprandial monocyte chemoattractant protein-1 response was lowered by fish oil and after weight loss (P < 0.001). This indicates that 1.1 g/d EPA+DHA supplied for 6 wk, in contrast to approximately 10 kg weight loss, does not improve markers of endothelial function and inflammation.