On Wednesday, the New York City Health Department asked local restaurants to stop using trans fats in their food. Health officials hope that reduced use of partially hydrogenated vegetable oils (which contain trans fats) would decrease the incidence of heart disease. Some chefs have lauded the move, saying trans fats have "an artificial, bad taste"; others worry that trimming trans will make familiar foods less delicious. What does trans fat taste like?
Probably nothing. Most scientists think that pure fat has no taste at all. That applies to trans fats, other unsaturated fats like sesame and corn oil, and saturated fats like butter and lard. The mouth senses five basic flavors: sweet, salty, sour, bitter, and umami (or glutamate, like MSG). Though some evidence suggests rodents can taste the flavor of fat, researchers haven't conclusively shown that human beings can detect fats with their taste buds.
That doesn't mean we can't tell when we're eating something fatty. All fats tend to share a certain oily texture that we can detect with our mouth's somatosensory receptors. These receptors, like those in the skin, respond to how something feels to the touch. Neurons in the brain respond to the oily texture regardless of its exact chemical makeup; to these cells, coconut oil "tastes" the same as peanut oil, corn oil, mineral oil, and silicone oil.
Then why does peanut oil taste like peanuts? Because most oils that you buy in the store have other components dissolved in the fat. Even if the fat in olive oil and peanut oil has no taste, characteristic impurities give each a distinct aroma. If a fast-food restaurant decided to make its French fries with cottonseed oil instead of soybean oil, the end product might smell (and taste) a bit different.
Trans fats are generally made by adding hydrogen to unsaturated vegetable oils to make them last longer. (An unprocessed soybean oil would go rancid much more quickly than its partially hydrogenated cousin.) Some taste-testers say they can detect a very slight difference between the unsaturated and partially hydrogenated versions of the same kind of oil, but nothing like an overwhelming "artificial" taste.
If restaurants were forbidden to use trans-fat-laden, processed soybean oil, they might fry their food in natural, unsaturated soybean oil. But since unsaturated fats go rancid relatively quickly, they would be more likely to break down into nasty-tasting chemical byproducts. Restaurants could also switch to another kind of naturally derived oil that lasts longer in the deep fryer, like cottonseed oil.
Explainer thanks James Hollis of Purdue University and Clay King of Texas Woman's University.