Many of us have by now heard of the health benefits of eating low−glycemic foods — like vegetables, grains, and nuts. These lead to a slow, steady increase in blood sugar, in contrast to the faster spike that comes from high−glycemic foods. But a new study suggests that munching on high−glycemic foods — like white bread, baked potatoes, and jelly beans — may actually reduce our arteries' ability to dilate fully, and ultimately lead to cardiovascular disease.

Researchers at the Chaim Sheba Medical Center in Israel looked at 56 patients who were overweight or obese, but none were diabetic or had any history of cardiovascular events in the past. After having fasted during the previous night, participants ate four different breakfasts, on four different mornings. The meals consisted of glucose (the highest in glycemic index), cornflakes, high−fiber cereal, or water (the lowest in glycemic index).

'[H]igh−glycemic index carbs are dangerous since they reduce or inhibit endothelial function.'

To track the function of blood vessels in response to the different meals, the researchers used a test called brachial artery flow−mediated dilation (FMD) to measure how well the endothelium, the layer of cells that lines the insides of arteries and veins, was working. If the endothelium is not functioning properly, this may lead to a greater likelihood of developing cardiovascular disease.

At 30 to 90 minutes after eating high−glycemic meals — glucose and cornflakes — participants' blood glucose was significantly higher than the other two meals, but after two hours, blood glucose was similar, regardless of meal type. Interestingly, two hours after eating, the FMD test revealed depressed blood vessel function in all groups, but this change was only significant after the high−glycemic meals of glucose and cornflakes.

"Based on our study, we do urge consumers to have low−glycemic index carbohydrates instead of high−glycemic carbohydrates for better health and less potential hazards for the vascular endothelial function," said study author Michael Shechter.

He underlines that "the main take−home message is that high−glycemic index carbs are dangerous since they reduce or inhibit endothelial function, which is the 'risk of the risk factors,' leading to atherosclerosis and potentially leading to heart disease."

The research is published in the June, 16 issue of the Journal of the American College of Cardiology.