Trans fat is the common name for a type of unsaturated fat with trans isomer fatty acid(s). A particular class of trans fats occurs, in small quantities, in meat and dairy products. Most trans fats consumed today, however, are industrially created as a side effect of hydrogenation of plant oils. The end effect of hydrogenation is to add hydrogen atoms to unsaturated fats, making them more saturated. These more saturated fats have a higher melting point and a reduced tendency for oxidation, resulting in a longer shelf-life.
Wilhelm Normann was a German chemist who introduced the hydrogenation of fats in 1901, which had a profound influence on the production of margarine. He patented the process in 1902.
In 1909, Procter & Gamble acquired the US rights to the Normann patent then, in 1911, they began marketing the first hydrogenated shortening, Crisco (composed largely of partially hydrogenated cottonseed oil). Further success came from the marketing technique of giving away free cookbooks in which every recipe called for Crisco.
Production of hydrogenated fats increased steadily until the 1960s as processed vegetable fats replaced animal fats in the US and other western countries. At first, the argument was a financial one due to lower costs; however, advocates also said that the unsaturated trans fats of margarine were healthier than the saturated fats of butter.
Trans fats in hydrogenated vegetable oil causes an increase in blood levels of low-density lipoprotein, or LDL, which is commonly known as “bad cholesterol.” LDL’s job is to transport cholesterol to the tissues of the body, and it can wreak havoc on its way.
“As LDL travels through the blood [carrying cholesterol to the tissues], it can deposit some of the cholesterol in the arteries, leading to plaques and atherosclerosis,” explains James Ntambi, a professor of biochemistry and nutritional sciences.
Ntambi notes that, on the other hand, HDL, or “good cholesterol,” transports cholesterol to the liver, where it is destroyed and excreted from the body. The polyunsaturated fat known as omega-3 fatty acid increases HDL levels and is considered heart-healthy. It is found in the oil of many types of fish.
More generally, all unsaturated fats — both polyunsaturated and monounsaturated — are considered healthful, in the sense that they do not increase risk for heart disease. Unsaturated fats are found in vegetable oils and nuts, in addition to fish.
Although Crisco has already developed a trans fat-free product and others are doing the same, “Nabisco and Kraft can’t buy as much [trans fat-free oils] as they need at this point,” says Barbara Ingham, an associate professor of food science.
To replace trans fats, many food producers are reaching for saturated fats such as palm oil, coconut oil and cocoa butter. Unfortunately, saturated fats don’t offer much of a health benefit over trans fats, if any. The USDA lumps trans fats and saturated fats together; both types raise LDL and are considered unhealthful.
Trans fat-free french fries are not significantly healthier, says UW–Madison nutritionist Sherry Tanumihardjo, because “even though restaurants in New York will be taking out the bad guy [trans fats], they are adding back saturated fats.
“Watching total fat consumption is important,” she emphasizes. “You’ve got to consider the total diet and exercise.”