There are many kinds of fat.  It is almost impossible to have a meal without fat, and though some fats are good for you, other fats are not.  Our bodies need fat for the following reasons:

• They provide essential fatty acids and can act as a nutrient
• Fats are a concentrated energy source in foods
• Fats transport fat-soluble vitamins A, D, E, and K along with some phytochemicals
• Fats contribute to taste and smell in foods
• Fats can stimulate our appetite
• Fats contribute to the feelings of satisfaction, contentment, and fullness
• Fats make foods softer or tender

Too much fat or the wrong kind of fat is not a good thing

Bad Fats:
Saturated Fat
Saturated fat derived from animal fat, coconut oil, cocoa butter, palm kernel oil, or palm oil is the worst kind of fat for you.  Saturated fat raises your bad cholesterol more than anything you could possibly eat.  If you want to reduce your bad cholesterol, stop eating or reduce your intake of saturated fat.

Trans Fats, Hydrogenated Fats, or Fatty Acids

Trans fatty acids are fats produced by heating liquid vegetable oils in the presence of hydrogen. This process is known as hydrogenation. The more hydrogenated an oil is, the harder it will be at room temperature. For example, a spreadable tub margarine is less hydrogenated and so has fewer trans fats than a stick margarine.
Most of the trans fats are found in refined foods, prepared baked goods, margarines, snack foods, and processed foods.  Fried foods, like French fries and onion rings, also contain a good amount of trans fat.
Trans fats also spark inflammation, an over activity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions. While you should limit your intake of saturated fats, it is important to eliminate trans fats from partially hydrogenated oils from your diet.

Good Fats:
Unsaturated Fat
Unsaturated fats are found in products derived from plant sources, such as vegetable oils (corn, soybean, olive), nuts, and seeds (sesame, sunflower). There are two main categories: Polyunsaturated fats which are found in high concentrations in sunflower, corn, and soybean oils, and monounsaturated fats which are found in high concentrations in canola, peanut, and olive oils. In studies in which polyunsaturated and monounsaturated fats were eaten and carbohydrates were eliminated, these good fats decreased bad cholesterol and increased good cholesterol.

Use only unrefined cold-or expeller-pressed oils, oils that have never been heated above 110F during processing. Another type of polyunsaturated fat is found in fish, which is often referred to as fish oil or omega-3 fatty acids. Nut oils are good sources of omega-3 fatty acids too and vitamin E. Walnut oil is highest in omega-3s, but beware, nut oils contain saturated as well as unsaturated fats.