NewYork-Presbyterian. The University Hospital of Columbia and Cornell.

-- Before you bite into that burger or devour that doughnut, first chew on this: New research shows that just one meal high in saturated fat can affect the body's ability to protect itself against some of the underlying causes of heart disease and stroke.

Australian researchers found that eating just one piece of carrot cake modified to be high in saturated fat and drinking a milkshake modified in the same way can reduce the body's ability to protect itself against heart disease.

The new study is published in the Journal of the American College of Cardiology.

The saturated fat in the cake and the milkshake (about 61 grams) hampered the ability of "good" cholesterol - high-density lipoprotein (HDL) - to do its job. That job is to protect the inner lining of the arteries from inflammatory agents that promote plaque, which clogs the vessels.

And the carrot cake and milkshake (made to be high in saturated fat for the study) also reduced the arteries' ability to expand and carry enough blood to organs and tissues, the researchers found.

High-Fat Meal vs. Low-Fat Meal

In the study, Dr. David Celermajer and his colleagues at the Heart Research Institute and Department of Cardiology at the Royal Prince Albert Hospital, University of Sydney, Australia, fed 14 healthy volunteers, ages 18 to 40, two meals eaten a month apart.

The volunteers gave blood samples before eating, three hours after eating, and again three hours after that.

The study participants were not told if they were eating high saturated-fat foods or not. The meals were the same, except one was made with highly saturated coconut oil, and the other with polyunsaturated safflower oil. Each meal featured a slice of carrot cake and a milkshake.

The fat content was high - about one gram of fat for every 2.2 pounds of body weight. But the meal with safflower oil had about 9 percent saturated fat, while the high saturated-fat meal contained nearly 90 percent saturated fat.

Saturated fat is the main dietary cause of high blood cholesterol, according to the American Heart Association, which recommends limiting saturated fat intake to 7 percent of total calories a day.

The amount of fat in the high-fat meal was equivalent to a 150-pound person eating a double cheeseburger, a large order of fries, and drinking a large milkshake, totaling about 68 grams of fat, the researchers said.

After three hours, the meal high in saturated fat had reduced the ability of the arteries to expand to increase blood flow. The polyunsaturated fat meal reduced this ability slightly as well, but the results weren't statistically significant.

When the researchers sampled the participants' blood six hours after eating, they found that the good (HDL) cholesterol's anti-inflammatory properties had decreased after the saturated fat meal but improved after the polyunsaturated fat meal.

Does One Meal Matter?

"Our group has measured the anti-inflammatory properties of HDL in this way for years," says Dr. Celermajer. "But this is the first time we have studied the effects of any meals on how the HDL might behave."

Alice H. Lichtenstein, senior scientist and director of the Cardiovascular Nutrition Laboratory at Tufts University in Boston, says the study results are "consistent with the current recommendation to restrict saturated fats. They give additional support [for following a diet with healthy fats].

"The effects [seen in the study] are transitory," she adds, "and there is not enough information on how this would impact cardiovascular risk" in the long run.

Dr. Celermajer acknowledges that the effects recorded in the study may be temporary. But, he adds, people should be concerned "because it might happen every time they eat a fatty meal - and thus not be fleeting at all."

New Study Validates Dietary Guidelines on Fat Intake

"The take-home, public-health message is this: It's further evidence to support the need to aggressively reduce the amount of saturated fat consumed in the diet," says study lead author Dr. Stephen J. Nicholls, now a cardiologist at the Cleveland Clinic in Ohio.

"This study helps to explain the mechanisms by which saturated fat supports the formation of plaques in the arterial wall, and we know these plaques are the major cause of heart attack and stroke," he says.

"It is a small study," Dr. Nicholls concludes, "but I think the findings have broad implication because diet and exercise are the cornerstones of all strategies for preventing heart disease."

Dr. Robert Vogel, a cardiologist and professor of medicine at the University of Maryland Medical Center, did not participate in the research, but agrees it provides "one more nail in the coffin" against eating diets high in saturated fat.

"This study helps to flesh out just why we shouldn't eat too much saturated fat," Dr. Vogel says. "Traditionally, we think of unhealthy foods as raising cholesterol or raising blood pressure, but this demonstrates that depending on what you eat, you can actually change the effect of HDL - typically thought of as 'good' cholesterol - from protective to detrimental. This opens up new insights and avenues for research."

Always consult your physician for more information.