Palm olein, a liquid form of palm oil used in cooking and baking, has been considered neutral in its effects on cholesterol but a new Danish study suggests the vegetable fat could behave more like lard in the body.
Men who ate a series of three diets, substituting a portion of their fats with olive oil, palm olein and lard, had lower levels of LDL ("bad") cholesterol and total cholesterol after the olive oil diet than after the other two.
Researchers did not show that the increased cholesterol levels had an effect on the men's health, but high cholesterol is thought to lead to an increased risk of having a heart attack.
The rise in cholesterol seen in this study "would increase the risk of heart disease by at least five percent," said Dr. Peter Clifton at the University of Adelaide in Australia, who was not involved in the work.
The research team, led by Tine Tholstrup at Copenhagen University, asked 32 normal-weight young men to replace a portion of the fats in their usual diets with palm olein, olive oil or lard during each of three weeks.
The order of the diets was randomly assigned and the study fats were contained in buns and cakes.
At the start and end of each week, the researchers collected blood samples and measured the men's weights.
After their week eating olive oil, the men had 4.5 percent lower total cholesterol levels, on average, than after the other two diets. The difference was largely due to lower LDL levels.
Lard, made from pig fat, had similar effects on blood cholesterol levels as palm olein.
Though previous studies have not always agreed on whether palm oil is bad for cholesterol levels, Clifton told Reuters Health in an email that he was not surprised by the results and that they provide a "very clear" answer.
"The majority of studies support the concept that palmitic acid in palm oil raises LDL cholesterol," Clifton wrote in an editorial that accompanied Tholstrup's study in the American Journal of Clinical Nutrition.
Palmitic acid is a saturated fatty acid found in a variety of oils, and is the primary fatty acid in palm oil.
High levels of LDL cholesterol, as opposed to high-density lipoprotein, or HDL, cholesterol, are considered bad for people's cardiovascular health.
But the authors write in their report that the increase in cholesterol after the palm olein diet was small, "and may not be of any clinical significance."
Tholstrup's team also tested the men for levels of C-reactive protein, used to predict cardiovascular disease risk, and did not find any differences among the three diets.
Tholstrup recently published a study that found cheese and butter, despite both being made from milk fat, produced differing effects on cholesterol levels.
"The role of saturated fat is controversial, as newer studies have not been able to find an association between intake of saturated fat and coronary heart disease," Tholstrup told Reuters Health in an email.
Still, Tholstrup said she recommends people choose cooking oils with unsaturated fat such as olive, rape seed, sunflower, soy bean and grape seed oils.
The current study was funded by the Malaysian Palm Oil Board, a government trade agency.