For years, butter has been a dietary villain blamed for high cholesterol and heart disease. Vegetable oil soon took butter’s place on many stovetops as a way to lower blood cholesterol levels.

But researchers at the University of North Carolina believe the benefits of the switch have been overestimated. Their study, published in the British Medical Journal, suggests that using vegetable oils high in linoleic (li-nə-ˈlē-ik) acid might not help prevent heart disease.

The researchers analyzed unpublished results from a nearly 50-year-old trial as well as published data from other studies. They found that while the vegetable oils lowered cholesterol, they didn’t necessarily reduce heart disease risk. In fact, some participants who had lower cholesterol actually had a higher risk of developing heart disease. The authors say the unpublished data led scientists to overestimate the benefits of reducing butter intake and substituting other types of oils in its place. Linoleic acid is found in varying levels in sunflower, soybean, corn, canola and other oils.

The study’s lead author also noted that randomized controlled trials, which are considered the most reliable standard for health research, have never shown that switching from butter to vegetable oil brings about a decrease in heart disease.

The researchers said future research should address why vegetable oils lower cholesterol levels but not heart disease risk. Some experts believe these oils can cause inflammation, which is a risk factor for heart disease, or promote plaque buildup in arteries.

Still, the best way to prevent heart disease is to maintain a healthy and balanced diet and exercise regularly.