Harvard Women's Health Watch

By the way, doctor: What is the least healthy fat to bake with?

Q. My mother and I have a friendly disagreement about fats for baking cookies. I say shortening is the unhealthiest because of its high trans fat content; my mother says butter or lard is worse. What's the verdict?

A. The easiest answer is that they're all unhealthy. Each contains high amounts of saturated fat or trans fatty acids (trans fat), which have adverse effects on blood cholesterol. Saturated fat raises LDL (bad) cholesterol, although it redeems itself somewhat by also boosting HDL (good) cholesterol. Trans fat raises LDL and lowers HDL — a worse combination. Both types of cholesterol circulate in the blood: LDL damages the arteries, while HDL seeks out the LDL and transports it to the liver for disposal from the body. National guidelines recommend that we get no more than 10% of daily calories from saturated fat and avoid trans fat as much as possible.

Animal fat, butter, dairy products, and some plant oils (such as coconut and palm oils) contain significant amounts of saturated fat. Trans fat is mostly manufactured, through a process called hydrogenation. This process increases shelf life and improves flavor stability, which is why trans fat is used so often in processed foods. Some animal products — butter, milk, cheese, beef, and lamb — contain small amounts of trans fat, but it's found in far greater quantities in vegetable shortenings, fried foods, some margarines, and many commercial foods (such as cookies, cakes, and snacks). Partially hydrogenated vegetable oils account for about 75% of the trans fat in the American diet.

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