The intestinal absorption of bacterial lipopolysaccharide (LPS) and dietary fat has been implicated in the development of metabolic endotoxemia. This study first compared the ability of polyphenol extracts from grape, cranberry, avocado and apple to interfere with pancreatic lipase and LPS in vitro. The grape extract displayed a higher inhibitory activity of lipase (IC50 = 8.6 ± 1.1 mg/ml) and LPS binding (IC50 = 90 ± 1.1 µg/ml). Then, a study was carried out in 12 normal weight and 17 overweight/obese subjects to determine the effect of this extract on the postprandial changes in plasma triacylglycerols, LPS and IL-6. The presence of small intestine bacterial overgrowth (SIBO), in which higher levels of bacteria and eventually LPS are present in the upper intestine, i.e. where dietary fat absorption occurs, was also evaluated. Compared with placebo, the grape extract did not affect postprandial triacylglycerolemia but decreased plasma LPS, without affecting the IL-6-associated inflammatory response. SIBO did not affect these variables.