Bad News for Olive Oil Converts

There appears to be no such thing as a "good" type of dietary fat. A study in Denmark has found that one high-fat meal almost doubles the peak concentration in the blood of a known risk factor for heart attack and stroke--irrespective of whether the fat is monounsaturated, polyunsaturated, or saturated. The finding, reported today in the journal Arteriosclerosis, Thrombosis and Vascular Biology, suggests that switching to monounsatured fats, a staple of Mediterranean diets, may not immediately lower risks from heart disease and stroke.

To try to explain why people fed on Mediterranean diets are less prone to heart disease than others, Danish researchers conducted six tests on 18 healthy young men over a 6-month period. In each test, they were fed a meal enriched in a particular type of fat--rapeseed oil or olive oil (monounsaturated), sunflower oil (polyunsaturated), and palm oil or butter (saturated)--and one low-fat meal for comparison. The researchers, led by biologist Lone Frost Larsen of the Royal Veterinary and Agricultural University in Frederiksberg, Denmark, then measured blood levels of factor VIIc--a known risk factor for heart attack. This coagulant plays an important role in the development of fibrin, a key participant in the formation of blood clots.

All the men had a doubling or more of the concentration of the active form of factor VIIc in the hours after they ate any of the high-fat meals. These results might be explained by the fact that Danish men normally eat a diet high in saturated fats, which could affect their acute responses to any type of fat, Larsen says. She is now testing whether putting the men on diets with little unsaturated fats for 3 weeks prior to the dietary tests will make a difference to their peak active factor VII levels.

Riitta Freese, a nutritionist from the University of Helsinki in Finland, who has done similar work, says such studies are important because they focus on the period right after eating, which "is the state we are in most of the time." She adds that most previous work has looked at another risk factor, triglycerides, and this is one of the few studies to examine factor VII levels.