Polyunsaturated fats in vegetable oils are healthful if they are left in the vegetables. Removing fats from vegetables makes them less stable so they turn rancid. To preserve their freshness, they are either processed with heat, which destroys the very unstable essential omega-3 fatty acids; or, even worse, they are converted into harmful partially hydrogenated fats. Hydrogen atoms are added to replace the unsaturated double bonds between carbons, to create a very stable, more solid fat that is similar to saturated fat but has a different chemical structure. Partially hydrogenated fats have been linked to increased risk for cancer and heart attacks.
Partially hydrogenated fats that you eat are deposited in your body fat. Lenore Kohlmeier of the University of North Carolina biopsied the fat in women's buttocks. She then followed these women for several years and showed that the amount of partially hydrogenated fats in a woman's buttocks predicts her susceptibility to developing breast cancer in the future (2). Other studies confirm this association (9).
Partially hydrogenated fats increase risk for heart attacks (8) by lowering blood levels of the good HDL cholesterol, raising levels of the bad LDL cholesterol and very bad Lp(a) and blocking arachidonic acid to cause clotting (3). Partially hydrogenated fats lower blood levels of omega-3 fatty acids to create a relative deficiency of the heart attack preventing fat to increase risk for a heart attack (4). They also raise blood levels of the bad LDL cholesterol that causes heart attacks (5).
Babies eat too much partially hydrogenated fats, too. A letter in the New England Journal of Medicine raised concern that infants eat too much of the partially hydrogenated fats that increase risk of heart attacks and cancers (6). Bruce Holub of the University of Guelph reported that partially hydrogenated fats account for 23 percent of the fat in baby cereals and 37 percent of the fat in baby cookies. The foods a woman eats determines what types of fats are found in her breast milk. Partially hydrogenated fats comprise 7.2 percent of the fat in Canadian women's breast milk and the combination of the large amount of partially hydrogenated fats in baby food and breast milk cause the average baby to get more than four percent of his fat from hydrogenated fats. Studies show that partially hydrogenated fats may slow growth and development in infants (7).
We have known for more than twenty years that trans fats increase your risk for heart attacks and possibly some types of cancers such as breast cancer. Wlter Willett, chairman of the Department of Nutrition as Harvard School of Public Health, reported that trans fats also increase your risk for getting diabetes (13).
Partially hydrogenated fats are still found in many prepared foods, such a french fries, doughnuts, frozen meals, cookies or crackers. Since labeling laws now require trans fat content to be listed in the Nutrition Facts panel, many manufacturers have eliminated them from their products. However, the laws allow a manufacturer to claim ZERO if there is less than one-half gram (.5g) of partially hydrogenated oil per serving. That doesn't sound like much, but if a serving size is one teaspoon or one cracker, it can add up to a lot of trans fats in a tub of margarine, a bowl of cereal or a bag of chips.
The only way to know whether a food contains any trans fats is to read the list of ingredients. If you see the words "partially hydrogenated" in front of any vegetable oil, the food contains trans fats. Look for another brand that does not include partially hydrogenated oils.
1) DB Allison, SK Egan, LM Barraj, C Caughman, M Infante, T Heimbach. Estimated intakes of trans fatty and other fatty acids in the US population. Journal of the American Dietetic Association 99: 2 (FEB 1999):166-174. Mean percentage of energy ingested as trans fatty acids was 2.6 percent and the mean percentage of total fat ingested as traits fatty acids was 7.4 percent.
2) Kohlmeier, L et al. Cancer Epidemiology October, 1997.
3) B Koletzko, T Decsi. Metabolic aspects of trans fatty acids. Clinical Nutrition 16: 5 (OCT 1997):229-237. trans fatty acids increase plasma LDL-cholesterol and lipoprotein (a) and reduce HDL-cholesterol concentrations, lower arachidonic acid.
4) E Larque, F PerezLlamas, V Puerta, MD Giron, MD Suarez, S Zamora, A Gil. Dietary trans fatty acids affect docosahexaenoic acid concentrations in plasma and liver but not brain of pregnant and fetal rats. Pediatric Research, 2000, Vol 47, Iss 2, pp 278-283.
5) M Noakes, PM Clifton. Changes in plasma lipids and other cardiovascular risk factors during 3 energy-restricted diets differing in total fat and fatty acid composition. American Journal of Clinical Nutrition, 2000, Vol 71, Iss 3, pp 706-712.
6) Holub BJ. Letter, NEJM, October 28, 1999 341(18);1396.
7) Koletzko B. Potential adverse effects of trans fatty acids in infants and children. Eur J Med Res 1995;1:123-5.
8) A Aro. Epidemiology of trans fatty acids and coronary heart disease in Europe. Nutrition Metabolism and Cardiovascular Diseases 8: 6 (DEC 1998):402-407.
9) BA Stoll. Breast cancer and the Western diet: Role of fatty acids and antioxidant vitamins. European Journal of Cancer 34: 12 (NOV 1998): 1852-1856.
10) Trans-Fatty Acids and Colon Cancer. Martha L. Slattery, Joan Benson, Khe-Ni Ma, Donna Schaffer, and John D. Potter. Nutrition and Cancer 39(2):170-175, 2001.
11) Bakery foods are the major dietary source of trans-fatty acids among pregnant women with diets providing 30 percent energy from fat. Journal of the American Dietetic Association, 2002, Vol 102, Iss 1, pp 46-51. SL Elias, SM Innis. Innis SM, British Columbia Res Inst Childrens & Womens Hlth, 950 W 28th Ave, Vancouver, BC V5Z 4H4, CANADA
12) Partially hydrogenated fats made from fish oils. Lancet, 3/10/01.
13) Science News, November 10, 2001, pp. 300-301
14) Cell membrane trans-fatty acids and the risk of primary cardiac arrest. Circulation, 2002, Vol 105, Iss 6, pp 697-701. RN Lemaitre, IB King, TE Raghunathan, RM Pearce, S Weinmann, RH Knopp, MK Copass, LA Cobb, DS Siscovick.
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