Cacao is rich in polyphenols such as (-)-epicatechin, and a colored component of cacao (cacao-red) is polyphenol, which is an antioxidant. These properties stimulated an investigation of the effects of cacao liquor polyphenols (CLP) on low-density lipoprotein (LDL) oxidation. The 2.2 '-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AMVN-CH2O)-induced oxidizability of LDL was assessed by monitoring the absorbance at 234 nm. In vitro. 0.1-0.5 mg/dL CLP prolonged the oxidation lag time of LDL in a dose-dependent manner. Compared with the controls, it was prolonged 1.7-fold in the presence of 0.1 mg/dL CLP, 2.9-fold at 0.2 mg/dL, 3.8-fold at 0.3 mg/dL, 5.4-fold at 0.4 mg/dL, and 6.4-fold at 0.5 mg/dL. Furthermore, we enlisted 13 male volunteers to consume 35 g delipidated cocoa. Venous blood samples were taken before and at 2 h and 4 h after consuming the cocoa. The oxidation lag time of LDL before cocoa ingestion was 59.0 +/- 6.3 min, but it was prolonged at 2 h after cocoa (68.3 +/- 6.0 min); before returning to the initial lag time (61.7 +/- 5.7 min) before consumption. Thus we have shown that cocoa inhibited LDL oxidation both in vitro and ex vivo.