Because fat is the most concentrated source of energy (i.e., calories) you can get from food, it's often vilified by popular weight-loss plans. Not all fat, however, deserves its bad reputation. Actually, good fats — like extra-virgin olive oil and canola oil — are an essential part of a healthy diet.

Did you know that fat plays a role in making vitamin D (which is actually a hormone) and other hormones, cushions your vital organs and bones, keeps your cells healthy, and aids in the absorption of vitamins A, E, and K? Good fats have other health benefits, too. Nuts and seeds, which are rich in healthy oils, can help reduce LDL (the "bad") cholesterol levels, while oily fish that contain omega-3 fatty acids can help lower high triglyceride levels (levels of fats that circulate in the blood), making the blood less sticky and thus less likely to clot and cause a heart attack or stroke.

The South Beach Diet encourages you to enjoy the good fats. Not only are they considered essential fats, meaning you must consume them in your diet to maintain good health, but they add flavor and texture to foods and help you feel satisfied. Certain fats, the so-called bad fats, should be avoided, since they contribute to heart disease and stroke. Here's a breakdown.

Good fats:

Unsaturated fat (mono- and poly-) exists in liquid form at room temperature. These are the good fats that are allowed on all Phases of the South Beach Diet. Unlike saturated and trans fats, unsaturated fats can lower your risk of heart disease and stroke.

Monounsaturated fats include extra-virgin olive oil and canola oil. Polyunsaturated fats include the omega-3s found in fish oil.

Bad fats:

Saturated fat exists in solid form at room temperature. It's found in animal products and some tropical vegetable oils, like palm kernel oil. Eating too much saturated fat can lead to high LDL ("bad") cholesterol, which can ultimately contribute to heart disease.

Trans fats are created when an unsaturated fat (like vegetable oil) is chemically altered so that it stays solid at room temperature. Consuming trans fats can lead to clogged arteries. Trans fats are found in processed foods like chips, baked goods, and fast foods. You'll see the words "hydrogenated" or "partially hydrogenated" on the ingredient label if trans fats are present. The amount of trans fats is also listed on the Nutrition Facts panel.

Note: Children under the age of two should not be on a fat-restricted diet, since fat is important for proper brain development.

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