Pandora's Lab: Seven Stories of Science Gone Wrong

by Paul A. Offit

Sometimes, as shown in the example on this page, the hydrogen atoms of an unsaturated fat are on the opposite side. Now the hydrogen atoms are said to be in a trans configuration. Trans, in Latin, means “on the other side.” When hydrogen atoms are on the opposite side, the molecule is straight. Now it’s much easier to stack one molecule on top of another. Molecules that stack neatly and tightly are easy to crystallize, converting a liquid into a solid. That’s why common vegetable shortenings, even though they are made of vegetable oils, stay solid in a can on your kitchen shelf. For the most part, large quantities of trans fats are not found in nature. They are created when hydrogen atoms are purposely added to unsaturated vegetable oils, a process called hydrogenation. The end product is typically referred to as a “partially hydrogenated vegetable oil.” The designation partially means that the product isn’t completely saturated or, said another way, is still unsaturated. It also means that the product is loaded with trans fats.