People who eat even one high-fat meal show more physical stress than those who eat a low-fat breakfast, a study says.

In the experiment, 30 healthy men were asked to fast for a night. The next day, one group was given a fast-food breakfast, while the other ate cereal with skim milk, cereal bars and non-fat yogurt.

Two hours later, they were given what researchers called standard stress tests, including a math exam, public speaking and holding their arms in ice water.

The group that had McDonald's for breakfast showed bigger changes in blood pressure, heart rate and other measures, said a student who helped conduct the study.

The senior author of the study, Tavis Campbell, said that it was not clear what caused the effect, or what its long-term implications are.