Australian researchers say that just one meal which is high in saturated fat can affect the arteries and stop the body from protecting itself against heart disease and stroke.

According to a team at the Heart Research Institute in Sydney, Australia, a meal with a comparable amount of calories but using healthy vegetable fat has far fewer ill effects.

Experts say the study illustrates how daily bad habits add up, over the years, and lead to heart disease, heart attacks and strokes and emphasises why we shouldn’t eat too much saturated fat.

They say the study demonstrates that depending on what you eat, you can change the effect of HDL - typically thought of as ‘good’ cholesterol - from protective to detrimental.

To clarify the point it is worth remembering that saturated fats include all animal fats found in meat and dairy products, as well as coconut and palm oils, whereas the majority of vegetable fats are polyunsaturated or mono-unsaturated.

In the study Dr. Stephen Nicholls and his colleagues fed 14 healthy volunteers aged 18 to 40, with one of two meals of carrot cake and a milkshake and then checked their blood.

The two meals were identical, except that one was high in coconut oil, a saturated fat, while the other was high in safflower oil, a healthier polyunsaturated fat.

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

The researchers found after three hours that in the volunteers who been given the saturated fat, the endothelium lining their blood vessels was less able to expand the arteries in order to increase blood flow.

Although the polyunsaturated meal also slightly reduced this ability the results were not statistically significant.

Six hours after the saturated fat meal, researchers found that high density lipoprotein, the HDL or “good” cholesterol, was less able to control inflammation inside the arteries.

HDL protects the inner lining of the arteries from inflammatory agents that promote plaque, which clogs the vessels. Inflammation is thought to be linked with heart disease.

By contrast, the polyunsaturated meal seemed to boost the anti-inflammatory abilities of HDL.

Dr. David Celermajer, Scandrett professor of cardiology at the Heart Research Institute, and Department of Cardiology, Royal Prince Alfred Hospital, University of Sydney, says the message is that saturated fat meals might predispose to inflammation of and plaque build up in the vessels.

Celermajer says that even though the effects recorded in the study may be temporary, people should be concerned because it might happen every time they eat a fatty meal and therefore not be temporary at all.

The study is published in the August 15 issue of the Journal of the American College of Cardiology.