WASHINGTON (CNN) -- A new study shows why fast food may speed up people's risk of clogged arteries that can lead to heart attacks.

Researchers at the Veterans Administration Medical Center in San Francisco have demonstrated that a certain type of fat, called oxidized fat, can accelerate the buildup of plaque in arteries. And many types of fast food -- hamburgers, pizza and French fries -- are loaded with oxidized fat.

While the study's conclusions -- reported in the latest issue of the American Heart Association's journal Arteriosclerosis, Thrombosis and Vascular Biology -- may seem obvious, the study's lead author, Ilona Staprans, says no one had actually tested the effect of oxidized fats in living animals to see if what logic would dictate were actually true.

But fast food isn't the only culprit. Researchers say many foods common in the Western diet contain oxidized fat, including baked products made with eggs and butter, deep- fried foods and foods processed by heat or drying. Dairy products, eggs and meat also contain high levels of oxidized fats.

Staprans' research team fed rabbits a high-cholesterol diet with a third of their calories from fat -- slightly lower in fat than most Western diets. Half of the rabbits were given a higher level of oxidized fat in their diet.

After just three months, the rabbits getting that diet had twice as many fatty streaks on their arteries as the other rabbits. They also had higher overall level of cholesterol, especially the "bad" LDL cholesterol linked with heart disease.

Researchers believe that oxidized fat combines with LDL cholesterol in arteries to promote buildup of plaque.

To avoid the negative impact of oxidized fat, researchers recommend modifying diets to avoid processed and fried foods. Health experts also say people should cook with healthier fats, such as olive or canola oil, and eat plenty of fresh fruits and vegetables, which are natural anti-oxidants.