Now, a Penn State study provides evidence that the optimum dietary fat isn't one that contains either more PUFAs or more MUFAs, but one that contains a proper balance of both to control cardiovascular risk factors.
In the Penn State study, detailed in the current issue of the Journal of the American Dietetic Association, two heart healthy oils, a new PUFA-rich sunflower oil (NuSun) and the more MUFA-rich olive oil, were compared in a diet designed to lower blood cholesterol levels.
Dr. Penny Kris Etherton, distinguished professor of nutrition who directed the study, says, "We expected the PUFAs, which are higher in the sunflower oil than the olive oil, to produce a greater reduction in total and LDL cholesterol levels in the study participants -- and they did. The surprise was the fact that the olive oil diet, which is also low in saturated fat, did not lower cholesterol levels compared with the average American diet. Also surprising was that the greater percentage of PUFAs in the NuSun sunflower oil diet did not increase LDL oxidation products that are risk factors for atherosclerosis."
The results are described in the paper, "Balance of Unsaturated Fatty Acids is Important to Cholesterol-Lowering Diet: Comparison of Mid-Oleic Sunflower Oil and Olive Oil on Cardiovascular Disease Risk Factors." The authors are Dr. Amy E. Binkoski, former Penn State doctoral student, Dr. Penny M. Kris-Etherton, distinguished professor of nutritional sciences, Dr. Thomas W. Wilson, assistant professor, University of Massachusetts Lowell, Margaret L. Mountain, dietitian, University of Pittsburgh Medical Center, and Dr. Robert J. Nicolosi, professor and director of the Center for Health and Disease Research, University of Massachusetts Lowell.
The researchers recruited 31 healthy men and women, ages 25 to 64, who had moderately elevated LDL cholesterol. The women's LDL cholesterol was in the 140 to 188 range and the men's was between 129 and 177.
The participants each ate three different diets: an olive oil-based diet, a NuSun sunflower oil-based diet or an average American diet. The two oil-based diets limited fat to 30 percent of calories and the average American diet had 34 percent fat calories. The volunteers ate each diet for four weeks, took a two-week break when they ate their usual diet and then moved on to the next diet. Blood samples were taken at the end of each diet period.
Analysis of the participants' blood samples showed that the NuSun sunflower oil diet significantly reduced total and LDL cholesterol levels compared with the average American diet. No significant differences were observed between the olive oil diet and the average American diet.
The ratios of total cholesterol to HDL cholesterol and LDL to HDL cholesterol were not significantly different among the three diets. Triglyceride levels also were similar among all three diets.
Some previous studies have shown a greater production of oxidation products following consumption of a high PUFA diet compared with a high MUFA diet. However, in this study, while the NuSun sunflower diet did not have a beneficial effect on LDL oxidation, there were no adverse effects despite the increase in PUFAs.
Kris-Etherton says, "Within the context of a moderate fat diet, it is becoming clear that a mixture of unsaturated fatty acids provides the greatest health benefits."
The study was supported by a grant from the National Sunflower Association and a National Institutes of Health grant to Penn State's General Clinical Research Center, which also participated in the study.