If you go on a low-fat diet, you will surely lower your cholesterol count, right?
Not necessarily, reports chemist Gary J. Nelson with the ARS Western Human Nutrition Research Center.
Among 11 healthy men aged 20 to 35 who volunteered for a study led by Nelson, cholesterol levels didn't change significantly—regardless of whether the men were on a low-fat or high-fat stint. Fat calories made up 39 percent of the day's total calories in the high-fat menus, while accounting for only 22 percent during the low-fat regimen—meaning that fat calories were nearly cut in half for those days.
Why didn't such a drastic drop in fat intake lead to a similar decrease in cholesterol?
"Perhaps because we didn't change the ratio of fats; that is, saturated to polyunsaturated to monounsaturated," says Nelson. "We stayed with 28 percent saturated fat—the kind in butter or lard; 33 percent monounsaturated; 6 percent monounsaturated transfats, as are found in some margarine; and 29 percent polyunsaturated fats—the kind in healthful cooking oils. Other minor fatty acids made up the remaining 4 percent.
"These findings," Nelson says, "should be of interest both to people who are trying to lower their cholesterol and to health care providers advising patients on how to change their diets to improve their cardiovascular health."
For the experiment, all volunteers ate the high-fat diet for 20 days. Then, six volunteers ate low-fat meals for 50 days, while the other five volunteers ate the high-fat foods—whole milk instead of nonfat and cream cheese, not jelly, on their breakfast bagels, for example. After that, the two groups crossed over to the opposite menus for the final 50 days of the study.
Nelson collaborated in the study with ARS chemists Perla C. Schmidt and Darshan S. Kelley at the Nutrition Center.—By Marcia Wood, Agricultural Research Service Information Staff.
"Fats Ratio May Be Crucial to Lowering Cholesterol" was published in the May 1999 issue of Agricultural Research magazine.