Just one trip through the drive-through for a fatty, fast-food meal could put your heart at risk.

A new study shows eating a fatty meal heightens the unhealthy effects of stress on the heart, like raising blood pressure.

Researchers found that people who ate a fatty, fast-food breakfast were more prone to suffer the negative effects of stress than those who ate a healthy, low-fat breakfast.

"What's really shocking is that this is just one meal," says researcher Tavis Campbell, PhD, assistant professor of psychology at the University of Calgary, in a news release. "It's been well documented that a high-fat diet leads to atherosclerosis [hardening of the arteries] and high blood pressure, and that exaggerated and prolonged cardiovascular responses to stress are associated with high blood pressure in the future."

"So when we learn that even a single, high-fat meal can make you more reactive to stress, it's cause for concern because it suggests a new and damaging way that a high-fat diet affects cardiovascular function."

Single Meal May Do Harm

In the study, 30 healthy adults fasted the night before and then ate either a high-fat breakfast from McDonald's consisting of a sausage McMuffin, an egg McMuffin, and two hash brown patties or a low-fat breakfast of dry cereal with skim milk, a cereal fruit bar, fat-free yogurt, and a glass of orange juice.

Both meals contained about 800 calories, but the high-fat meal had 42 grams of fat, and the low-fat meal had 1 gram of fat. A sodium supplement was added to the low-fat meal to even out the difference between the two meals.

Two hours later, the participants completed several stress-inducing tasks while researchers measured their cardiovascular response, including blood pressure, heart rate, and resistance within blood vessels. The tasks were designed to provoke mental and/or physical stress, such as completing a public speaking exercise about something emotionally provocative or holding a hand in ice water.

The results showed that regardless of the task, the blood pressure response was greater among those who ate the high-fat meal than those who ate the low-fat one.

Researchers say it's unclear how a single high-fat meal can sensitize the body to stress, but the results suggest a new way in which high-fat diets may contribute to heart disease.

This article was reviewed by Louise Chang, MD.

SOURCES: Jakulj, F. Journal of Nutrition, April 2007; vol 137: pp 935-939. News release, University of Calgary.