In order to understand obesity, you have to understand fat. We are all born with a certain number of fat cells. The number of cells we have multiplies during the growing years and levels off as we approach adulthood. But fat is another term that can be confusing because there are two different kinds: dietary fat and body fat.

Dietary fat is a part of food. Also called: Lipids, Monounsaturated fat, Polyunsaturated fat, Saturated fat. You want to have a little bit of fat in your diet because it serves as a major source of energy for your body. It is used to make cell membranes and compounds in your body that control blood pressure, heart rate, blood clotting, and other body functions. It carries certain vitamins from your food throughout your body.
Fat gives you healthy hair, skin, and nails. Dietary fat supplies essential fatty acids, linoleic and linolenic acids, which are especially important to infants and toddlers, it helps the brain develop and proper growth. Fat also helps you to feel full and tells your brain that it is time to stop eating.

The Dietary Guidelines for Americans 2005 recommend that Americans keep their total fat intake within certain limits. This limit is defined as a percentage of your total calorie needs.

Age Group	Total Fat Limits
Children ages 2 to 3	30% to 35% of total calories
Children and adolescents ages 4 to 18	25% to 35% of total calories
Adults, ages 19 and older	20% to 35% of total calories

Statistically, a nonobese person has about 25 billion to 30 billion fat cells; a moderately obese person has approximately 60 billion to 100 billion; and a seriously obese person has close to 200 billion fat cells.

But not all fats are the same. You should try to avoid 2 kinds of fat. The first is Saturated fats such as butter, solid shortening, lard and fatback. And the second is Trans fats, found in vegetable shortenings, some margarines, crackers, cookies, snack foods and other foods made with or fried in partially hydrogenated oils

Important note : Dietary fat also plays a major role in your cholesterol levels. Fat is required for regulation of cholesterol metabolism.

Cholesterol is a fat-like substance that is necessary in many physiological processes such as, a component of cell membranes, the production of bile acids (which aid in food digestion), and in the production of sex hormones. An excess of cholesterol in the blood, however, can lead to deposits in the walls of blood vessels and reduce blood flow to major arteries, which can lead to a heart attack.

Body fat is a part of the human body and what scientists mean when they refer to a person’s weight or body composition.Please visit here for more about body fat.