high fat meal decreases blood flow progressively over the next 4 hours; Cocoa antioxidants prevented this effect almost completely
Endothelial cells lie shoulder to shoulder like a carpet lining blood vessel walls. These cells have to react to changes in the volume of blood flow pushing blood vessels wider; otherwise there is pressure on the heart and blood pressure rises. Poor function of endothelial cells is seen in coronary heart disease, hypertension, diabetics, smokers, and people with high cholesterol. Failure of these cells to function properly can be very dangerous. Endothelial dysfunction is a key event in the development of atherosclerosis; hardening of the arteries due to a build up of cholesterol plaque within arterial walls (a major cause of death).
Eating a high fat meal prevents these cells from functioning. Scientists from Magdeburg University Hospital performed a placebo-controlled, randomized, double-blind cross-over clinical trial. 18 healthy people were fed a high fat meal with either cocoa rich in antioxidants or cocoa lacking the antioxidants. They then were crossed over to the other group (cocoa with antioxidants or cocoa without). The high fat meal decreased endothelial function and reduced blood flow progressively over the next four hours. But the same meal along with the cocoa antioxidants had much less of a negative effect. The study is published online ahead of print on December 8th, 2010 in the journal Heart and Vessels. 

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