Previously, vegetable oils such as soybean, sunflower and corn were regarded as heart-healthy because of their high levels of linoleic acid, a polyunsaturated fatty acid. HNE is incorporated into fried food in the same concentration as it forms in the heated oil. Also, Csallany and her colleagues have found three toxic HNE-related compounds (known as HHE, HOE and HDE) in heated soybean oil. They will present their work at a poster session from 9 a.m. to 2 p.m. Wednesday, May 4, at the 96th annual meeting of the American Oil Chemists Society in the Salt Lake City Convention Center.
"HNE is a well known, highly toxic compound that is easily absorbed from the diet," said Csallany. "The toxicity arises because the compound is highly reactive with proteins, nucleic acids--DNA and RNA--and other biomolecules. HNE is formed from the oxidation of linoleic acid, and reports have related it to several diseases, including atherosclerosis, stroke, Parkinson's, Alzheimer's, Huntington's and liver diseases."
Csallany's work underscores the risk of repeated heating, or reusing, highly unsaturated oils for frying because HNE accumulates with each heating cycle. In future studies, Csallany and her colleagues plan to determine how long polyunsaturated oil must be heated at lower temperatures in order to form HNE and its related compounds. The study was funded by the University of Minnesota.
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The randomized clinical trial included 120 adults, ages 30 to 65 and all were members of the target population for food-based approaches to lowering cholesterol with moderately high LDL levels, between 130 and 190 mg/dL. They were randomly divided into two diners' groups: 61 ate the conventional diet, while 59 ate the plant-based diet. Each weekday for a month, they visited a research dining hall for a specially prepared, carefully weighed, chemically analysed lunch or dinner.
The study required that participants maintain a constant weight so that any changes in blood cholesterol would be attributable to the diets themselves -- not to any changes in weight brought on by the diets. When changes in weight were observed, the participants' calories were changed accordingly to help them stay stable. In general researchers tended to add calories to the meal plan over the course of the study as participants were observed to be more likely to lose weight than to gain weight on both diets.
The scientists also requested that no one change exercise habits, saying: "If you are a marathon runner, keep running marathons. But if you're a couch potato, we need you to stay a couch potato."
Gardner, a 20-year vegetarian who specializes in nutrition and preventive medicine, expects a plant-based diet combined with weight loss and exercise to achieve even more impressive cholesterol-lowering results.
Gardner's research collaborators include Ann Coulston; Lorraine Chatterjee; Alison Rigby, PhD, MPH; Gene Spiller, PhD, and John Farquhar, MD.
Stanford University Medical Center integrates research, medical education and patient care at its three institutions -- Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford.
The findings are published in the May 3 issue of the Annals of Internal Medicine.
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