WASHINGTON, D.C. (WPVI) --A study, which sat in a basement for decades, is now the latest to question long-standing advice on saturated fat.
The study compared people eating saturated fats from butter, milk and meat to people who ate a lot of polyunsaturated fat.
Much of the saturated fat in their diets was replaced with corn oil, an unsaturated fat common in many processed foods, including margarine, cakes, cookies and dressings.
The unsaturated fat group did lower their bad cholesterol. But they didn't see fewer deaths due to heart disease.
Some experts say this shows how the science on food is always changing.
"Even our own U.S. Dietary Guidelines, which tend to be very conservative, is now beginning to recognize that a lot of that old advice about cholesterol and eggs was not good advice," says Dr. Steve Nissen, a Cleveland Clinic cardiologist and patient advocate.
Dr. Nissen says this doesn't mean you can chow down on fatty foods.
But it does suggest saturated fat may not be as bad as once thought.