Consuming a variety of dietary fats--saturated, polyunsaturated and monounsaturated--is the key to maintaining healthy blood cholesterol levels when reducing fat intake, according to a leading researcher.
Eating one fat to the exclusion of others throws off the balance between good and bad cholesterol, according to Gustav Schonfeld MD, director of the Lipid Research Center, Washington University School of Medicine, St. Louis.
Schonfeld addressed 200 California Dietetic Assn. dietitians attending a symposium in Los Angeles on dietary fats and disease recently.
High levels of low-density lipoproteins (LDLs), a bad cholesterol, damage the cardiovascular system by depositing plaque in the arteries, which can lead to heart disease. On the other hand, high levels of high-density lipoproteins (HDLs), a good cholesterol, seem to have a protective effect by helping the body better metabolize dietary fats.
Schonfeld says no one dietary fat has either all good or all bad effects on fat transport systems found in the blood.
"If you severely limit or exclude one, you run the risk of overconsuming another, thereby tipping the balance," he said.
"For instance, polyunsaturated fats lower the damaging LDL-cholesterol, but they also lower the heart-protective HDL-cholesterol," Schonfeld said.
"Diets very high in carbohydrates and very low in fats decrease LDL-cholesterol, but also cause two negative effects that can increase the risk for heart disease--a decrease in HDL-cholesterol and an increase in triglycerides."
Saturated Fats Not All Bad
Ironically, saturated fats, long considered the villain in heart disease, increase both the damaging and the protective cholesterols.
"It's still uncertain, but a minimum amount of saturated fats may be needed to help form HDL, which in turn helps the body better manage a high-fat diet," Schonfeld said.
New research shows that when compared to saturated fats, monounsaturated fats--found in many foods and in olive oil--lower the harmful LDL levels without lowering the beneficial HDL or changing triglyceride levels. Until recently, monounsaturated fats were thought to have no effect on blood fats.
"Since all forms of dietary fats seem to have both potentially desirable and undesirable effects, it's wise to try to achieve a balance of fats--saturated, polyunsaturated and monounsaturated--when reducing fat intake to 30% of calories," Schonfeld said.