Shining the Spotlight on Trans Fats

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For years, only true diet detectives knew whether a particular food contained trans fat. This phantom fat—the worst fat for the heart, blood vessels, and rest of the body—was found in thousands of foods. But only people who knew that the code phrases “partially hydrogenated vegetable oil” and “vegetable shortening” meant that trans fat lurked in the food were aware of its presence.

Now, at least for foods with food labels, anyone can tell. Since January 1, 2006, the U.S. has required that trans fat must be listed on food labels along with other bad fats (saturated fats) and good ones (unsaturated fats). (1) (For more information on different types of fat, read “Fats & Cholesterol: Out with the Bad, In with the Good”.)

The addition is a victory for Harvard School of Public Health researchers who helped sound the alarm about trans fat in the early 1990s (2, 3) and who advocated that it be explicitly listed on food labels. After much equivocation by the FDA and intense lobbying against the addition by parts of the food industry, the FDA finally approved adding trans fat to food labels.

This small, one-line change in a massive federal rule has sparked a major makeover of the American food supply. The FDA once estimated that approximately 95 percent of prepared cookies, 100 percent of crackers, and 80 percent of frozen breakfast products contained trans fat. (1) Now that trans fat must be listed on food labels, many companies have removed them from their products.

Of course, many foods don’t come with labels, such as foods sold in bakeries, cafeterias, schools, and restaurants. Because consumers cannot tell whether these unlabeled foods contain trans fats—and, in turn, cannot make the choice to avoid trans fat-laden foods—many cities and states have passed or are considering laws to eliminate trans fats in these foods. California’s governor recently signed legislation to phase out trans fats from restaurants by 2010 and from baked goods by 2011, the first state in the nation to do so. New York City became the largest city in the nation to require its restaurants, cafeterias, and schools to go trans free (the city has a “Trans Fat Help Center” to help food professionals comply), and other cities and towns, such as Boston, are following its lead.

The shift follows the growing realization that trans fats are even worse for the heart and blood vessels than saturated fats.

Where Do Trans Fats Come From?

Trans fats are a type of mostly man-made fat that the food industry loves, but our hearts and blood vessels don’t.

In the late 19th century, chemists discovered that they could add hydrogen atoms to unsaturated fats by bubbling hydrogen gas through vegetable oil in the presence of a nickel catalyst. (4) This was far more than a chemical curiosity. Partially hydrogenated oils don’t spoil as easily as nonhydrogenated fats. They can withstand repeated heating without breaking down. And the process can turn a liquid oil into a solid, which allowed for easier transportation and wider uses; this solid fat was also much less expensive than solid animal fats.

These characteristics were attractive to food makers. Over the last several decades, partially hydrogenated oils became a mainstay in margarines, commercially baked goods, and snack foods. When saturated fat was fingered as a contributor to high cholesterol, companies such as McDonald’s and Dunkin’ Donuts switched from beef tallow to partially hydrogenated vegetable oil for frying French fries and donuts.

At the time, switching from butter or lard (both of which contain high amounts of saturated fat) to a product made from healthy vegetable oil seemed to make sense. Intake of trans fat increased dramatically. Before the advent of partial hydrogenation, the only trans fat that humans consumed came from eating cows (or dairy products), lamb, and deer; in ruminants like these, bacteria living in the stomach make small amounts of trans fat. But due to the growth of partial hydrogenation, by the early 1990s, trans fat intake in the United States averaged 4 to 7 percent of calories from fat.

In 1981, a group of Welsh researchers speculated that trans fat might be linked with heart disease. (5) A 1993 Harvard study strongly supported the hypothesis that intake of partially hydrogenated vegetable oils contributed to the risk of having a heart attack. (3) In that study, the researchers estimated that replacing just 2 percent of energy from trans fat with healthy unsaturated fat would decrease the risk of coronary heart disease by about one-third. An influential symposium on trans fat later in the 1990s drew public attention to the issue.

Today we know that eating trans fats increases levels of low-density lipoprotein (LDL, “bad” cholesterol), especially the small, dense LDL particles that may be more damaging to arteries. It lowers levels of high-density lipoprotein (HDL) particles, which scour blood vessels for bad cholesterol and truck it to the liver for disposal. It also promotes inflammation, (6) an overactivity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions. Eating trans fat also reduces the normal healthy responsiveness of endothelial cells, the cells that line all of our blood vessels. In animal studies, eating trans fat also promotes obesity and resistance to insulin, the precursor to diabetes.

This multiple-pronged attack on blood vessels translates into heart disease and death. An analysis of the health effects of industrial trans fats conducted by researchers with the Harvard School of Public Health Department of Nutrition indicates that eliminating trans fats from the U.S. food supply could prevent up to 1 in 5 heart attacks and related deaths. That would mean a quarter of a million fewer heart attacks and related deaths each year in the United States alone. (7) (As noted above, trans fats do naturally occur in dairy foods and meat from ruminant animals, but trans fats from these sources do not make up as significant a part of the American diet, so they are not as much of a public health concern.)

Big Changes in the Food Industry

Many food makers have realized that consumers, having the new information on the food label, would avoid products containing trans fat. Fearing lost sales, many companies have found ways to make their products without partially hydrogenated oils.

Some margarines have been virtually trans fat-free for several years. Major chip makers now use trans-free oils for making tortilla chips and other crunchy snacks. Frozen food makers have introduced frozen fried chicken products without trans fat. A few grocery store chains never carried products that contain trans fat. And several major restaurant chains have reformulated their products to reduce trans fats.

Keeping Track of Trans Fat

Now that the once-ubiquitous but invisible trans fats are listed in bold print on food labels, it’s easier to spot them in packaged foods. Keep in mind, though, that according to the FDA, a product claiming to have zero trans fat can actually contain up to a half gram. (Canada set a different standard of zero as under 0.2 grams.) So you may still want to scan the ingredient list for “partially hydrogenated vegetable oil” and “vegetable shortening,” and look for an alternative product without those words, especially if it’s something you eat regularly.

The Dietary Guidelines for Americans recommends limiting intake of trans fats, but doesn’t offer a specific target. The federal Institute of Medicine is a bit more specific. It says “there are no known requirements for trans fatty acids for specific bodily functions,” and so trans fatty acid consumption should “be as low as possible.” How to do this? Look for products that don’t contain any. This is easier now that more and more companies are competing for the attention of trans-free shoppers. It’s harder to avoid trans fat in restaurants, since they are not required to provide nutrition information about the food they serve. One strategy is to avoid deep-fried foods, since many restaurants continue to use partially hydrogenated oils in their fryers. You may be able to help change this behavior by asking your server, the chef, or manager if the establishment uses trans-free oils.

One final note: Just because a food has been prepared without partially hydrogenated oil doesn’t necessarily make it healthy, cautions Walter Willett, chair of the Department of Nutrition at the Harvard School of Public Health. “It can be trans-free and still contain a lot of sugar, easily digestible (low fiber) carbohydrate and starch, or saturated fat, which isn’t a good choice.”

Tips for Lowering Trans Fat Intake

Olive oil

  • Choose liquid vegetable oils, or choose a soft tub margarine that contains little or no trans fats.
  • Avoid eating commercially prepared baked foods (cookies, pies, donuts, etc.), snack foods, and processed foods, including fast foods. To be on the safe side, assume that all such products contain trans fats unless they are labeled otherwise.
  • When foods containing partially hydrogenated oils can’t be avoided, choose products that list the partially hydrogenated oils near the end of the ingredient list.
  • To avoid trans fats in restaurants, one strategy is to avoid deep-fried foods (since many restaurants still use partially hydrogenated oils in their fryers) and desserts. You may be able to help change these cooking practices by asking your server, the chef, or manager if the establishment uses only trans-free oils and foods.


1. Food Labeling: Trans Fatty Acids in Nutrition Labeling. Government Publishing Office.

2. Ascherio A, Hennekens CH, Buring JE, Master C, Stampfer MJ, Willett WC. Trans-fatty acids intake and risk of myocardial infarction. Circulation. 1994; 89:94-101.

3. Willett WC, Stampfer MJ, Manson JE, et al. Intake of trans fatty acids and risk of coronary heart disease among women. Lancet. 1993; 341:581-5.

4. Katan MB, Zock PL, Mensink RP. Trans fatty acids and their effects on lipoproteins in humans. Annual Review of Nutrition. 1995; 15:473-93.

5. Thomas LH, Jones PR, Winter JA, Smith H. Hydrogenated oils and fats: the presence of chemically-modified fatty acids in human adipose tissue. American Journal of Clinical Nutrition. 1981; 34:877-86.

6. Mozaffarian D, Pischon T, Hankinson SE, et al. Dietary intake of trans fatty acids and systemic inflammation in women. American Journal of Clinical Nutrition. 2004; 79:606-12.

7. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. N Engl J Med. 2006 Apr 13;354(15):1601-13.

8. Sizzling test results boost demand for new soybean oil. Iowa State University.

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