When arteries are fully healthy, the endothelium responds to demands for increased blood flow by emitting nitric oxide and other chemicals. The nitric oxide relaxes the smooth muscle in the arterial walls, allowing the artery to dilate and boost blood flow. Just one fatty meal, however, can affect endothelial cells, suppressing their nitric oxide output and causing arteries to become rigid and stay narrow.
In the experiment, eight healthy men consumed high-fat meals. The researchers tested the subjects before and after the meals to check the functioning of the endothelial cells that line the brachial artery, the artery that supplies blood to the arm. The men took turns engaging in different practices before their meals - either resting for 16-18 hours, exercising at a moderate level of intensity for a set period of time, or exercising strenuously for the same period.
After each high-fat meal, the men were tested, under conditions that required increased blood flow, to see how responsive their brachial arteries were. The men who rested before eating experienced a 10 percent reduction in artery diameter after the fatty meal, and there was no arterial dilation in response to increased blood-flow needs.
The men who exercised moderately also had a 10 percent decrease in artery diameter after eating, but their artery was able to dilate somewhat when they needed more blood flow. Those who exercised vigorously had no reduction in artery diameter after their meal, and experienced normal artery dilation. Exercise's protective effect occurred despite tests that showed increased levels of fat and cholesterol in the blood of these same men after eating.