Beyond the Zeitgeist

If you’re beyond the Zeitgeist, you grew up with the original trans fat, and probably used it yourself: Crisco. It was perfect for baking, courtesy of a process, developed around the turn of the 20th century, that transforms liquid fats—oils—into solids. Margarine is another product of the process. So, alas, are trans fats.

The process, called hydrogenation, is chemical, and for me chemistry is right up there with algebra in mind-numbing opacity. Nevertheless, what with New York City banning trans fats in restaurants amid dire warnings that they’re really bad for your health, it seems to me useful to try to understand them. Particularly when, reading the fine print on a butter substitute that trumpets “No Trans Fats” in large type on its label, I find “partially hydrogenated vegetable oil” high on the list of ingredients.

Before the nasty nature of trans fats was understood, everyone thought Crisco and margarine, having started as plant oils and being in fact only partially saturated through the hydrogenation process, were much healthier than the lard and butter they replaced. Besides, they have a much longer shelf life, Crisco behaves better in baking and margarine is spreadable right out of the refrigerator.

How does hydrogenation produce these effects? With apologies to Wikipedia: Fats are fatty acids. Chemically, they are composed of long chains of hydrogen and carbon atoms. Saturated fats (solid at room temperature, like butter and lard) have all their hydrogen-atom slots filled; unsaturated fats don’t. Unsaturated, plant-based oils can be monounsaturated, e.g., olive oil, or polyunsaturated, with more hydrogen atoms left out of each molecule. The hydrogenation process adds those “missing” hydrogen atoms; partial hydrogenation leaves some slots for hydrogen atoms empty, so the fat, like Crisco, is easily workable at room temperature.

Unfortunately for us, partial hydrogenation has another effect, as well. It twists the connections between the carbon atoms (which, in the absence of a hydrogen atom to bond with, double-bond with each other), throwing off the original arrangement of the molecule so that the hydrogen atoms it does contain, which were originally neatly lined up on one side of the chain of atoms, now oppose each other across—trans, in Latin—the chain.

It’s these twisted sisters that do the damage—specifically, increase your chances of a heart attach by increasing your blood levels of “bad” (LDL) cholesterol and decreasing your levels of “good” (HDL) cholesterol.

So butter may not be worse for you than margarine after all. And when you pick up that butter substitute, read the fine print. You may even conclude that butter is better.