Harvard Health Letter

Ask the doctor: How do trans fats harm health?

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.

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