The skinny on fat is simple enough: Americans eat too much of it, and as a result, wear too much of it.

Today we're eating fewer fatty meats, whole dairy products and other foods rich in saturated fats -- the kind that most significantly raise cholesterol, clog arteries and contribute to heart disease and stroke. In fact, Americans are consuming less fat as a percent of total calories than we did 20 years ago. But as a nation, we're actually getting fatter and eating more overall calories than ever before.

One reason might be our reliance on "low-fat" and "fat-free" labels. Today, 9 in 10 Americans regularly buy lower-fat versions of food products, which sometimes contain more calories (albeit fewer fat calories) than the original versions.

Some "no-fat" or "low-fat" products contain as many calories as their original versions per serving; a handful can even have a few calories more. Many people consume larger quantities of low-fat foods, believing that they are "healthier." But a 10 or 15 calorie difference per cookie can tip the scales (and not in your favor) if you overindulge. So it's important to read the entire food label, not just the information on fat.

Until the last few years, more calories weren't the only concern in low-fat foods. Previously lower-fat versions contained oils that underwent a chemical process known as "hydrogenation," in which a liquid vegetable oil that's naturally high in unsaturated fatty acids (and therefore heart-healthier) is transformed to a more solid and saturated form.

Hydrogenation changes oil in two ways: Besides making oils more saturated, it creates trans fatty acids — molecules that get twisted and out of shape during heating. These trans fats can raise the levels of low-density lipoproteins (LDLs), the so-called "bad" cholesterol, sometimes as much as saturated fats do in some people. Meanwhile, trans fatty acids do not increase levels of high-density lipoproteins (HDLs), the "good" cholesterol that is responsive to monounsaturated fatty acids found in olive and canola oils. And some studies suggest that the chemical change induced in fatty acids by hydrogenation also may affect cell function, thereby increasing the risk of cancer.

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Read the label
Until the last few years, more calories weren't the only concern in low-fat foods. Previously lower-fat versions contained oils that underwent a chemical process known as "hydrogenation," in which a liquid vegetable oil that's naturally high in unsaturated fatty acids (and therefore heart-healthier) is transformed to a more solid and saturated form.