Trans fatty acids (TFAs) are a type of unsaturated fat defined by a specific chemical configuration. This structure alters their physical properties, making them desirable for the food industry but hazardous for human consumption. The presence of artificial TFAs in processed foods has been strongly linked to an increased risk of chronic disease, prompting a global effort to eliminate them from the food supply. Health warnings and regulatory action primarily focus on these industrially produced versions, although some trans fats occur naturally.
The Science of Trans Fats
Fatty acids are long chains of carbon atoms; a double bond makes them unsaturated. In nature, nearly all unsaturated fatty acids exist in a cis configuration, where hydrogen atoms around the double bond are on the same side. This creates a natural kink in the molecule, preventing tight packing. Consequently, cis unsaturated fats, like those in vegetable oils, are typically liquid at room temperature.
Trans fatty acids have a trans configuration, meaning the hydrogen atoms are on opposite sides of the double bond, resulting in a straighter, more rigid molecule. This straighter shape allows the fat molecules to stack more closely, giving them a semi-solid or solid consistency at room temperature. The primary source of artificial trans fats is partial hydrogenation, a manufacturing process where liquid vegetable oils are heated and treated with hydrogen gas and a catalyst. This process stabilizes the oil but inadvertently converts some remaining cis bonds into the trans form.
Small amounts of trans fats also occur naturally in meat and dairy products from ruminant animals, such as cows and sheep. These fats are formed by bacteria in the animals’ stomachs and include specific types like conjugated linoleic acid (CLA). While all trans fats share the same chemical structure, the health effects of these naturally occurring TFAs are not considered as harmful as the industrially produced versions.
Identifying Major Dietary Sources
The vast majority of trans fat consumed comes from industrially produced sources, specifically foods containing partially hydrogenated oils (PHOs). Manufacturers historically favored PHOs because they are inexpensive, extend the shelf life of products, and provide a desirable texture to baked goods and fried foods. They were widely used in commercial baking and frying operations.
Foods traditionally high in artificial trans fats included:
- Commercial baked goods, such as cakes, cookies, pies, and biscuits.
- Pre-packaged snack foods, including crackers, microwave popcorn, and certain chips.
- Fried foods from fast-food restaurants.
- Frozen pizzas and refrigerated dough.
- Stick margarines.
Consumers must know how to identify these fats on nutrition labels, even where regulations are strict. In the United States, a product can be labeled as having “0 grams trans fat” if it contains less than 0.5 grams per serving. This allowance means trans fat intake can accumulate quickly if a person eats multiple servings or different products with trace amounts. The most reliable identification method is checking the ingredient list for the specific phrase “partially hydrogenated oil,” which indicates the presence of artificial trans fats regardless of the nutrition panel amount.
Impact on Cardiovascular Health
Artificial trans fats are uniquely harmful because they inflict a dual negative effect on blood cholesterol levels, directly impacting cardiovascular health. They actively raise low-density lipoprotein (LDL) cholesterol, often called “bad” cholesterol, in the bloodstream. LDL contributes to the buildup of fatty deposits, known as plaque, within artery walls (atherosclerosis). This plaque narrows and hardens the arteries, increasing the risk of blockages that can lead to a heart attack or stroke.
Simultaneously, trans fats decrease high-density lipoprotein (HDL) cholesterol, commonly referred to as “good” cholesterol. HDL plays a protective role by picking up excess cholesterol from the arteries and transporting it back to the liver for removal. By increasing harmful LDL and decreasing protective HDL, trans fats create an unfavorable cholesterol profile that significantly elevates the risk of coronary artery disease.
Trans fats are also linked to systemic inflammation, a significant factor in chronic disease development. Consumption of artificial trans fats increases inflammatory markers in the body. Chronic inflammation can damage the inner lining of blood vessels, further contributing to cardiovascular events and potentially increasing the likelihood of developing metabolic conditions, including Type 2 diabetes. The World Health Organization (WHO) estimates that trans fat intake leads to more than 500,000 deaths from cardiovascular disease globally each year.
Global Regulatory Measures and Consumer Avoidance
In response to scientific evidence of harm, governments and international bodies have implemented policies to remove artificial trans fats from the food supply. The WHO launched the REPLACE action package, a strategic guide for countries to eliminate industrially produced trans fats. A common policy is a mandatory national limit of two grams of industrially produced trans fat per 100 grams of total fat, or a complete ban on the use of partially hydrogenated oils.
In the United States, the Food and Drug Administration (FDA) determined that partially hydrogenated oils (PHOs) are no longer “Generally Recognized as Safe” (GRAS) for human consumption, effectively banning the primary source of artificial trans fats. Many countries, including Denmark (the first to mandate restrictions), have seen a substantial decline in trans fat content and corresponding reductions in cardiovascular disease deaths. Today, nearly half of the world’s population is covered by policies limiting trans fat in food.
Despite broad regulatory actions, consumers can take steps to minimize their personal intake. The most direct approach is limiting the consumption of processed and pre-packaged foods where artificial trans fats historically resided. When preparing food at home, use naturally occurring, non-hydrogenated oils such as olive, canola, or sunflower oil instead of solid fats or shortenings.