The truth about trans: hydrogenated oils aren't guilty as charged - trans fats

Nutrition Action Healthletter, March, 1988 by Elaine Blume

The Truth About Trans

They're in Ritz Crackers, Hostess ho Hos, Oreos, Kellogg's Pop Tarts, and hundreds of other processed foods. They're the principal ingredient in margarines and shortenings. They're hydrogenated fats.

Many journalists--and a few researchers--view hydrogenated fats with great suspicion. And more than a few consumers won't touch margarine. Some aren't sure why they distrust the stuff. Others know exactly why. Margarine contains "trans" fats.

Manufacturers hydrogenate (add hydrogen to) liquid oils to make them semi-solid. In the process, some hydrogens in the fats get rearranged. Scientists refer to fats with the ordinary arrangement as "cis." The new ones are called "trans" (see diagram).

Despite the rumors, there is little good evidence that trans fats cause any more harm than other fats. Though new questions can always be raised, some of the standard accusations can be laid to rest.

Does Trans Equla Trouble? In the Goldbecks' Guide to Good Food, Nikki and David Goldbeck state that trans fats "are suspected of interfering with fath metabolism, disrupting normal heart functions, enhancing fatty deposits in the arteries, inhibitng the production and utilization of substances in the body which influence the immune system, and reducing the body's ability to rid itself of carcinogens, drugs, and other toxins." Other authors have raised similar concerns.

Much of the anxiety over trans fats stems from their reputation as "unnatural." Yet ruminants, such as cows and sheep, hydrogenate oils in one of their several stomachs. So although most of the trans fat people consume today is man-made, about 5 to 20 percent comes from beef, lamb, and dairy products.

In rat studies, trans fats appear safe. Animals absorb them just as well as they absorb other fats and oils. [1] And rats fed high levels of trans fats for 46 generations lived as long as other rats, reproduced as well, and appeared normal. [2]

Hydrogenated Hearts. But these studies have not stilled all fears. Some claim, for example, that trans fats raise blood cholesterol levels. That's a serious charge against trans-fat-containing margarines, which are marketed as heart-healthy.

In some animals, trans fats do raise blood cholesterol; in others, they don't. [3] But it makes sense to look most closely at the evidence from human studies.

Although some human studies suggest that trans fats do raise blood cholesterol, most of these had serious flaws. Several, for example, used an unusual fat with two trans groups. This fat is not present to a significant extent in commercial margarines or oils. [4,5]

Only a few studies were well designed, and these showed that hydrogenated (trans-containing) and non-hydrogenated fats produced similar cholesterol levels. [6,7] However, even in the weaker studies, trans fats did not raise cholesterol as much as saturated fats. [8] "In general," says Fred Mattson, a noted researcher at the University of California in San Diego, "studies show trans fats to have the same effect on human blood lipid levels as cis fats."

Cancer Worries. In 1978, Mary Enig and others at the University of Maryland examined the rise in our vegetable fat intake since 1910. This rise, they asserted, was linked to n increase in the number of people who developed or died of cancer, especially breast and colon cancer, during that period. The trans fats in vegetable fats, suggested the scientists, could best account for the "significant positive correlation" with cancer rates. [9]

At most, associations of this type can only provide clues about the cause of a disease. In no way do they prove cause and effect. But this particular analysis had serious flaws.

For example, experts pointe out that most cancer rates, including deaths from colon cancer, had remained essentially stable during much of the period in question. What's more, the authors failed to consider other changes in America's eating habits over more than half a century. Commenting on the paper, John C. Bailar III, editor-in-chief of the Journal of the National Cancer Institute, concluded, "Evidence for a [cancer--causing] role of the trans fatty acid component is no better--and no worse--than for countless other dietary components." [10]

In most animal studies, trans fats don't increase the incidence of tumors. But non-hydrogenated corn, safflower, and sunflower oils, which contain high levels of polyunsaturated fats, are relatively strong tumor promoters, at least in animals. [11]

Unfortunately, few people are familiar with these studies. Instead, many have heard of the cancer "correlation," but not of its flaws. So the rumor that trans fats cause cancer persists.

Cell Membranes. Animal studies show that trans fats, like other fats, may beome incorporated into the membranes that surround all cells in the body. Some fear that the incorporated trans fats might alter the normal passage of substances into and out of cells, perhaps permitting carcinogens to enter cells with greater ease.