It has long been known that simple carbohydrates that turn into sugars are not good for your heart or your health - but until now, scientists have not understood exactly what they do to the body.

Now a landmark study by Dr. Michael Shechter of Tel Aviv University's Sackler School of Medicine and Sheba Medical Center's heart institute (in cooperation with its endocrinology institute) - just published in the Journal of the American College of Cardiology - demonstrates exactly how these foods increase the risk of heart disease.

Like the medical warnings on packets of cigarettes, this new research could lead to food labeling that educates people about the effects of a harmful diet.

Shechter and colleagues used brachial reactive testing - which employs an arm cuff to visualize arterial function in real time - to examine the inside of the students' arteries while they ate a variety of foods. They clearly found that foods with a high glycemic index distended brachial arteries for several hours.

While elasticity of arteries throughout the body is found in young people and is beneficial, this sudden stretching of the endothelium inside the arteries over time causes harm. A sudden expansion of the artery wall can cause a number of negative health effects, including reduced elasticity - which can lead to heart disease or sudden death.

"It's very hard to predict heart disease," says Shechter, "but doctors know that high glycemic foods rapidly increase blood sugar. Those who binge on these foods have a greater chance of sudden death from heart attack. Our research connects the dots, showing the link between diet and what's happening in real time in the arteries."

The researchers divided 56 healthy volunteers into four groups. Over the course of a month, one group ate bowls of cornflakes mixed with milk, a second were served a pure sugar mixture, the third ate bran flakes, while the last group was given a placebo (water).

The results were dramatic. Before patients in the four groups ate, their arterial function was essentially the same. After eating, except for the placebo group who drank water, all had reduced arterial functioning. Enormous peaks, indicating arterial stress, were found in the high-glycemic-index groups: the cornflakes and sugar groups.

"We knew high glycemic foods were bad for the heart. Now we have a mechanism that shows how," says Shechter. "Foods like cornflakes, white bread, french fries and sweet drinks all put undue stress on our arteries. We've explained for the first time how high-glycemic carbohydrates can affect the progression of heart disease."

During the consumption of foods high in sugar, there appears to be a temporary and sudden dysfunction in the endothelial walls of the arteries. The health of the tissue layer inside the arteries can be traced back to almost every disorder and disease in the body, says Shechter. It is "the riskiest of the risk factors."

He advises avoiding simple carbohydrates as much as possible in favor of foods like oatmeal, fruits and vegetables, legumes and nuts, which have a low glycemic index. Their beneficial effect is boosted by exercising daily for at least half an hour.