Q. I know I’m not supposed to consume trans fats, but I’m not sure how they damage health. Can you explain it?
A. Despite what you might have heard for decades, not all types of fats in your diet are bad for you. Monounsaturated and polyunsaturated fats are “good fats.” We need the good fats in our diet, in moderation. (Any type of fat contains a lot of calories, and pigging out on “good fats” can lead to unhealthy weight gain.) In contrast, saturated and trans fats are “bad fats.”
Trans fats are largely man-made. Over the past century, they have appeared in many foods as a byproduct of chemical processes used to help prolong the shelf life of those foods. They are abundant in hard margarines, fried fast foods (like French fries), and many commercial baked goods.
Aim for zero trans fats.
In the 1990s, nutrition scientists (primarily here at Harvard) showed that high levels of trans fats in the diet raise blood levels of LDL (bad) cholesterol as much as saturated fat does. This research led the FDA to require that the Nutrition Facts label on packaged foods include the amount of trans fat intake. The U.S. National Academy of Sciences has declared that there is no safe level of trans fats. Several countries and U.S. cities have passed laws restricting the amount of trans fats in foods. Several manufacturers, including Frito-Lay, Kraft, and Pepperidge Farms, have reduced the trans fats in their products. So have several restaurant chains, including Legal Sea Foods and Ruby Tuesday.
So, be prudent about trans fats. It’s almost impossible to completely avoid them. And they’re not like arsenic: one swallow will not kill you. But eating a lot of them over time does put you at risk—and offers you absolutely no health benefits.
—Anthony L. Komaroff, M.D.
Editor in Chief
Harvard Health Letter