June 7, 2001 University Park, Pa. – Three diets high in monounsaturated fats from either olive oil, peanut oil, or peanuts and peanut butter had the same favorable effects on low density lipoproteins (LDLs, the "bad" cholesterol) as a low-fat diet in a laboratory study led by a Penn State researcher.
The study was the first to evaluate and compare LDL susceptibility to oxidation when the test subjects ate an average American diet, a low-fat diet or a higher monounsaturated fat diet. Oxidation of LDLs is thought to play an important role in the development of atherosclerosis or hardening of the arteries. Increasing LDL's resistance to oxidation is thought to delay the progression of the disease.
Dr. Penny Kris-Etherton, distinguished professor of nutrition and leader of the study, says, "Results from this study suggest that Americans may be able to eat the same amount of fat as they are used to without adversely affecting some cardiovascular disease markers as long as they change the type of fats they consume."
The study is detailed in a paper, "Low Fat and High Monounsaturated Fat Diets Decrease Human Low Density Lipoprotein Oxidative Susceptibility in Vitro," published in the current (June) issue of the Journal of Nutrition. Kris-Etherton's co-authors are Rebecca L. Hargrove, who earned an M.S. degree in nutrition at Penn State; Dr. Terry Etherton, distinguished professor and head of the dairy and animal sciences department; Dr. Thomas A. Pearson, adjunct professor in the Penn State Department of Nutrition and professor of community and preventive medicine, University of Rochester Medical Center; and Dr. Earl H. Harrison, U.S. Department of Agriculture, Human Nutrition Research Center.
The study compared the standard American diet (35 percent calories from fat) with a low fat diet (25 percent calories from fat), and three higher monounsaturated fat (35 percent calories from fat) diets containing either olive oil, peanut oil or peanuts and peanut butter.
In the study, 9 men and 13 women with normal total cholesterol and LDL cholesterol ate each of the experimental diets for three and a half weeks. The subjects had blood drawn twice at the end of each diet period. The LDL was extracted from each blood sample and then subjected to oxidation in the laboratory. The researchers noted the amount of time it took for oxidation to begin, the rate at which oxidation proceeded and the amount of oxidized fatty acid produced.
When the subjects ate the standard American diet, their LDLs oxidized faster than when they ate either the low fat diet or any of the higher monounsaturated fat diets. All three higher monounsaturated fat diets were equivalent to the low-fat diet -- and better than the standard American diet -- in the length of time it took for oxidation to begin and in the amount of oxidized fatty acid produced.
Kris-Etherton says, "A few clinical studies have been conducted on this subject and more are currently on-going."
In the meantime, before these clinical studies have been completed, the researchers say the current study provides evidence that both low fat diets and diets higher in monounsaturated fatty acids from olive oil, peanut oil, peanuts and peanut butter decrease LDL-oxidative susceptibility and thereby contribute to a decreased risk of coronary heart disease (CHD). Kris-Etherton notes that these results offer people trying to manage their CHD risk factors with more choices. A low-fat diet isn't the only alternative.
"A Mediterranean-style diet that focuses on fruit, vegetables, monounsaturated oil, nuts, legumes and grains, and includes only small portions of meat would produce the beneficial changes seen in our study," the Penn State researcher says.
"Or people could switch to low fat dairy products, eat peanut butter instead of butter or full fat cream cheese, use olive oil-based salad dressings, sprinkle nuts on vegetables instead of butter or margarine and use nuts in salads or stews instead of meat."
The research study was supported by a grant from the National Institutes of Health and the Peanut Institute.
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