Trans fat linked to increase in cholesterol

04/15/04

An animal study bolsters the government's concern about foods with hydrogenated oils

Washington, DC The government's direct assault on obesity and cardiovascular disease has at least one target in its sights: "trans fat," better known as the by-products hydrogenated oils, hydrogenated vegetable oils, margarine, partially-hydrogenated oils, and vegetable shortening.

Trans Fat Food Content Must Be Labeled In 2006

Trans fatty acids (or "trans fat") are found in some margarines, crackers, candies, baked goods, cookies, snack foods, fried foods, salad dressings, and many processed foods. In 2003, the Food and Drug Administration (FDA) issued a regulation requiring manufacturers to list trans fatty acids, or trans fat, on the Nutrition Facts panel of foods and some dietary supplements. Food manufacturers have until Jan. 1, 2006 to list trans fat on nutrition labels. The FDA estimates that by three years after that date, trans fat labeling will have prevented from 600 to 1,200 cases of coronary heart disease and 250 to 500 deaths each year.

Outside the US, some European countries and Australia have already taken steps to reduce trans fat content in the food supply, as the literature has suggested for some time that trans fat is linked to an increase in bad cholesterol (LDL-C) and a reduction in good cholesterol (HDL-C).

What Are Trans Fats?

Trans fats are produced through hydrogenation, a chemical process by which hydrogen is added to unsaturated fatty acids. Hydrogenation gets rid of double bonds. In doing so, the molecular configuration of the fat molecule can change from the natural "cis" to the "trans" configuration.

A New Study

A team of physiologists have speculated that trans fat supplementation in a swine model would raise the total to high density lipoprotein cholesterol ratio TC/HDL-C, a major factor in the progression of cardiovascular disease. The authors of the study, "Trans Fat Increases Total/HDL Cholesterol Ratio in a Porcine Model of Cardiovascular Disease," are Kyle K. Henderson, R. Scott Rector, Ying Liu, Tom R. Thomas, James R. Turk, M. Harold Laughlin, and Michael Sturek, all from the University of Missouri, Columbia, MO. They will present their findings at the American Physiological Society's (APS) (www.the-aps.org) annual scientific conference, Experimental Biology 2003, being held April 17-21, 2004, at the Washington, D.C. Convention Center.

Methodology

The primary interest of this research lab is the cardiovascular system and the beneficial effects of exercise training. For some of their studies, these investigators use a swine (pig) model. Swine are an excellent vehicle for understanding the cardiovascular system as their hearts are similar in size, structure and function as our own.

Pigs that consume a diet of 2% cholesterol (approximately 40 eggs) and coconut oil (approximately 90% saturated fat) so that 46% of their daily caloric intake is derived from fat, develop early stages of cardiovascular disease in 20 weeks. This effect is similar to that seen in 30-year old humans.

For this study the researchers were interested in developing a blood lipid profile that could lead to advanced stages of cardiovascular disease. Seven pigs (Yucatan and Ossabaw) were placed on four different diets. For 30 weeks, pigs consumed a 2% cholesterol diet supplemented with coconut oil that derives 75% of their kcal from fat. These pigs were then taken to the catheter lab to assess atheroma formation in the coronary artery. Atheroma formation was similar to that observed with the previous studies that lasted 20wks and derived 46%kcal from fat. Researchers then examined the effects of various two week diets before sacrificing the pigs. For two weeks the pigs returned to the 46% high fat diet as a "wash-out" for the previous diet. The pigs were then placed on a 2% cholesterol diet but the coconut oil was substituted with hydrogenated soybean oil, which increased the trans-fat content from 0% to 48% but reduced the saturated fats from 90% to 20%. This trans fat diet derived 75% of the kcal from fat.

Finally, since previous data suggested that once a day feeding leads to a more atherogenic blood profile, the researchers investigated whether twice a day feeding would alter the lipid profile vs. the standard once a day feeding using the 46% kcal coconut oil based diet.

Blood was taken at the conclusion of the various diets 6hrs after a meal. Blood samples were measured for: TC, TG, HDL-C, LDL-C, VLDL and LDL1-5. The ratios TC/HDL-C and LDL-C/HDL-C were also calculated.

Results

When the researchers compared the zero trans vs. the trans diets (same kcal from fat but zero trans vs. 48% trans fat) they found that:

  • in two weeks, there was a significant increase in total cholesterol (TC) and LDL-C;

  • the ratios TC/HDL-C and LDL-C/HDL-C were significantly increased with the trans fat diet in two weeks;

  • triglycerides after the various meals (6hrs post-meal) were significantly greater after T75 vs. C75;

  • there were no differences in Yucatan vs. Ossabaw responses; and

  • at the end of the study, in an Ossabaw pig, the circumflex coronary artery had an advanced lesion.

    Conclusions

    The trans fat diet (T75) significantly increased total cholesterol, LDL-C, TC/HDL-C and LDL-C/HDL-C ratios in two weeks compared to the isocaloric diet with zero trans fat (C75). Further triglycerides were significantly greater six hours after the trans fat meal vs. the isocaloric zero trans meal. Increasing the fat content did not augment an atherogenic blood lipid profile. Therefore, these data suggest that a diet high in trans fat has the potential to promote the rapid development of cardiovascular disease in swine models.

    Source: Eurekalert & others

    Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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