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Food for Thought

Janet Raloff
Food for Thought

Stronger Proof That Trans Fats Are Bad

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Scientists have warned us that eating lots of trans fats, a common component in a variety of fatty foods, can lead to heart problems. A recent study has strengthened the caution, as researchers have investigated these fats in the bodies of first-heart-attack patients.

Whenever food manufacturers transform vegetable oils into solids—via a process called hydrogenation—trans fats are created. For the sake of texture and preservation, trans fats show up in most margarines, shortening, and foods cooked with partially hydrogenated oils. Different types of trans fats also occur naturally in dairy foods and some meats, but they tend to have health benefits (SN: 03/03/01, p. 136: The Good Trans Fat).

Trans fats have raised concern for decades, as research has increasingly suggested a causal link between the hydrogenated fats and heart problems. Just as saturated fats and cholesterol do, trans fats raise people's concentrations of artery-clogging low-density lipoprotein (LDL) cholesterol (SN: 11/10/01, p. 300: Available to subscribers at Trans Fats). In addition, trans fats have been known to lower high-density lipoprotein (HDL) cholesterol, the beneficial cholesterol.

Both trans fats and other fats are blamed, in part, for more than 500,000 heart disease deaths in the United States each year, according to the U.S. Food and Drug Administration. Many studies, however, suggest that the adverse effects of trans fats are worse than those of saturated fats, says Walter C. Willett, an epidemiologist from the Harvard School of Public Health. Adding to this argument is a new study looking at people's body fat.

Trans in fat

From 1995 to 1997, scientists from the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Adelaide, South Australia, acquired dietary information as well as fat biopsy samples from 79 people. Each had just had a first heart attack. The researchers obtained similar information and biopsy samples from 167 residents of Adelaide without heart problems. The researchers inquired specifically about the participants' type and amount of fat intake. The heart patients and healthy individuals were also matched for age, gender, and socioeconomic background.

Analysis revealed that trans fats from both animal and vegetable sources were significantly more abundant in the fat tissues of heart attack patients than in the healthy volunteers. The finding supports the idea that trans fats increase the risk of heart disease. "It doesn't necessarily absolutely confirm cause and effect, but it's certainly very damning evidence," says study coauthor Manny Noakes.

Moreover, trans fats are "possibly worse" for the heart than saturated fats are, Noakes adds, as the relationship of abundant trans fats with heart risk remained even after the scientists statistically accounted for the effect of saturated fats in the participants' diets. The findings appear in the April Journal of Nutrition.

Noakes says that the significance of her team's findings stems from their measurement of trans fats in body fat, which correlates with a relatively long-term record of trans fat intake. Earlier studies based on blood-fat data and other observations about people with heart disease linked cardiovascular disease with trans fat consumption. The older data and the stronger CSIRO study together are "sufficiently strong to make a recommendation to reduce the level of trans fat in the food supply," says Noakes.

Disappearing act

Indeed, trans fats' adverse effects on people's health have prompted a few countries to urge consumers away from trans fat-rich foods. Last year, Denmark became the first country to announce that it would ban hydrogenated fats, says Noakes. The United States has since requested food manufacturers to label quantities of hydrogenated trans fat in most foods (No Hiding Most Trans Fats). Australia also plans trans fat labeling of foods so people at risk of heart disease, type 2 diabetes, and other conditions can avoid excessive consumption of trans fats.

During the CSIRO study, major margarine producers in Australia voluntarily and coincidentally replaced trans fats in their products with small amounts of saturated fats. Margarine had been the primary vegetable source of trans fats and had accounted for between 36 and 64 percent of the country's total trans fat intake.

The removal of trans fats from the product during the study gave Noakes' team an opportunity to assess how quickly trans fats clear from body fat. The data show that the body clears such fats "unexpectedly" rapidly in people with and without heart disease, Noakes says. The concentration of trans fats in the body fat of people who continued to eat margarine dropped by some 20 percent within a few months.

What happened to the trans fats? "As we change our diet, the nature of our [body] fat changes too," because it's constantly being used for energy, Noakes explains.

The quick disappearance of trans fats from fat tissue is "not surprising, but still is nice to see," says Willett. Overall, he says, the findings from the CSIRO study strengthen the argument that "trans fats should be removed from the food supply as rapidly as possible." Indeed, he finds it troubling that some of the U.S. food industry hasn't followed the lead of European food producers, who have nearly eliminated trans fats from their products. He describes hydrogenated fat as a "metabolic poison with zero nutritional value." He asks, "At what point does . . . feeding it to people without their consent become criminal?"


Manny Noakes

CSIRO Health Sciences and Nutrition

Clinical Research Unit

PO Box 10041

Adelaide BC

South Australia 5000


Walter C. Willett

Harvard School of Public Health

Department of Nutrition

Building II, Room 311

651 Huntington Avenue

Boston, MA 02115
Further Reading

Baylin, A., et al. 2003. Adipose tissue alpha-linolenic acid and nonfatal acute myocardial infarction in Costa Rica. Circulation 107(April 1):1586-1591. Available at [Go to].

Dashti, N., et al. 2002. Trans polyunsaturated fatty acids have more adverse effects than saturated fatty acids on the concentration and composition of lipoproteins secreted by human hepatoma HepG2 cells. Journal of Nutrition 132 (September):2651-2659. Available at [Go to].

Gorman, J. 2001. Trans fats. Science News 160 (Nov. 10):300-301. Available to subscribers at [Go to].

Raloff, J. 2003. No hiding most trans fats. Science News Online (July 19). Available at [Go to].

______. 2001. The good trans fat. Science News 159(March 3):136-138. Available at [Go to].

______. 1997. Genetically engineering a healthier margarine. Science News Online (May 31). Available at [Go to].

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