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Tip
Sheet: Medical Science & Health Tip sheets highlight timely news and events at Washington University in St. Louis. For more information on any of the stories below or for assistance in arranging interviews, please see the contact information listed with each story. For comments on the Medical Science & Health news tips service, please contact the editor, Jim Dryden at (314) 286-0110 or drydenj@msnotes.wustl.edu. Corn oil reduces cholesterol absorption Media assistance: Jim Dryden - (314) 286-0110 Source: Richard Ostlund's Web page - (314) 935-8286 Related: Nutrition article: Phytosterols in human nutrition [St. Louis, Mo., July/August 2002] - Researchers at Washington University School of Medicine in St. Louis found that commercial corn oil can significantly reduce the amount of cholesterol absorbed from food. They reported their findings in the June 2002 issue of the American Journal of Clinical Nutrition. Cooking oils have been the subject of much scientific study in recent years. Some nutritionists believe that the fats in some oils are healthier than others, and there has been a push for cooks to use certain vegetable oils -- such as olive or canola oil -- and to avoid oils deemed less healthy.
"Scientists have known about the effects of phytosterols on cholesterol for 50 years," says Richard E. Ostlund Jr., M.D., professor of medicine and lead investigator of the study. "Phytosterols lower cholesterol and increase the percentage of HDL, or good, cholesterol. But prior to this study, we had no evidence that phytosterols naturally appearing in our diets could affect cholesterol absorption." Now we do. When study subjects were fed a test meal containing a specific amount of cholesterol, they absorbed about 38 percent less cholesterol when the meal included corn oil that contained phytosterols. "We started with standard, commercial corn oil, but then we used a technique to remove the phytosterols," Ostlund says. "When a person ate the same test meal, with and without the phytosterols, they absorbed different levels of cholesterol, absorbing significantly less from meals containing phytosterols." To make sure phytosterols were the key, the researchers tested three different types of oil. First, they used commercial corn oil. Then, they took that oil and removed the phytosterols using a technique called competitive saturation adsorption. When they had compared commercial corn oil to the same oil with phytosterols removed, they then took the "purified" oil and added back phytosterols. The resulting reconstituted oil also cut the absorption of cholesterol by amounts similar to the commercial corn oil. "It's pretty clear from our studies that phytosterols have a role in cholesterol absorption that is not related to the fatty acid content of the corn oil," Ostlund says. "The bottom line is that these substances may be much more important than previously thought." Ostlund says it is likely that other vegetable oils have similar effects on absorption of cholesterol because they contain phytosterols, too. "All vegetable oils contain phytosterols to some degree, but the amount that's present depends upon the way the oil is refined and manufactured," he says. Some manufacturing processes remove phyotosterols from cooking oil. Ostlund says this study shows that the purification process probably is a bad idea. He also says that because phytosterols in the diet have a significant effect on absorption of dietary cholesterol, he would like to see phytosterol content included on food labels. The discovery that phytosterols in the diet can lower cholesterol absorption also may explain why diets rich in fruits and vegetables are so good for cholesterol levels. "I think it's always much better to try to obtain nutritional through diet, both because it's cheaper and because many people tend to get more benefit from substances in their diet than they do from taking dietary supplements," Ostlund says. "It seems clear both that manufacturing processes that keep plant sterols in oils and diets that are rich in vegetable products may be able to significantly lower cholesterol levels." |
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