Cooking with vegetable oil to reduce saturated fats can lower cholesterol, but it may not help curb the risk of heart disease or add years to your life, U.S. researchers say.
Plenty of previous research has linked polyunsaturated fat in vegetable oil, nuts and seeds with a lower risk of heart disease. Based on these studies, people have been routinely advised to replace animal fats like butter, cream and lard with plant-based oils made from corn, soybean, canola and olives.
But this has never been proven by gold-standard studies that randomly assigned people to specific diets to see how different foods and fats impacted health and longevity, said Dr. Christopher Ramsden, lead author of the current study.
When Ramsden's team examined data from an experiment that did just this with more than 9,400 people, they found the lower cholesterol from swapping saturated fats for vegetable oils didn't lead to improved survival.
"In fact, participants who had greater reductions in cholesterol had higher, rather than lower, risk of death," Ramsden, a researcher at the National Institutes of Health and the University of North Carolina at Chapel Hill, said by email.
The researchers studied data from 1968 to 1973 on residents of one nursing home and six mental hospitals in Minnesota, ranging in age from 20 to 97.
Residents were randomly assigned to either a diet that replaced saturated fat with corn oil and margarine made from corn oil, or to a control group that ate meals high in saturated fat from animal fats, common margarine and shortenings.
After switching to the vegetable oil diet, residents had a nearly 14 percent drop in cholesterol levels, compared with just a 1 percent dip for the control group, researchers report in The BMJ, April 12. But lower cholesterol didn't turn out to be helpful.
Researchers looked at participants' total serum cholesterol, which includes triglycerides, LDL cholesterol and HDL cholesterol. The American Heart Association says a total serum cholesterol of less than 180 mg/dL is ideal.
For every 30 mg/dL reduction in cholesterol, however, people's risk of death rose 22 percent, based on an analysis of autopsy reports available for the study population as of 2015.
In addition, the vegetable oil diet wasn't tied to a reduced risk of atherosclerosis.
Limitations of the study include the fact that the experimental diet included almost twice as much linoleic acid - the main polyunsaturated fat in vegetable oil, nuts and seeds - as a typical American diet.
Also, because the researchers used concentrated vegetable oils, the findings might not apply to people who consume lots of linoleic acid by eating nuts or seeds.
Even so, the findings suggest that saturated fat and linoleic acid, one particular type of polyunsaturated fat, may not differ much in their effects on vascular health, said Dr. Lennert Veerman, a public health researcher at the University of Queensland in Australia who wrote an editorial accompanying the study.
More research is still needed to fully understand which fats are best, Veerman said by email.
"People should focus on recommendations that are not in doubt: avoid trans fats, added sugars, and sodium, (and) eat a varied diet rich in a variety of vegetables, whole fruits, whole grains, sea foods, lean meats, eggs, legumes, and nuts, seeds and soy products," Veerman said.
As for vegetable oil, "it may or may not be better for blood vessels compared to saturated fat, but there is no evidence that it does harm and there is no need to stop using it," Veerman added.