Last week I began to answer a question concerning the role of fats in the body and in the diet. I mentioned that fats are an important source of energy whose basic chemical structure makes it possible to pack a lot of energy into a small amount of space. In fact, fats contain more than twice as much energy (9 Kcals/gram) as carbohydrates (about 4 Kcals/gram). Because of this, fats are an ideal source of stored energy in that they provide a large amount of energy but don't take up much space.

Fats supply essential fatty acids for growth and other regulatory and metabolic functions. These essential fatty acids must be ingested from the food we eat to have a proper diet. Fats also carry the fat soluble vitamins A, D, E and K, all of which are essential for proper body functioning. In the body, fat acts as insulation to help maintain body temperature in normal ranges. It also helps support various internal organs and gives shape to the body.With all of these important functions, it is sometimes difficult to understand why health professionals continue to encourage Americans to decrease the total amount of fat in the diet. The American Heart Association has been preaching this doctrine for years and the American Cancer Society has joined the ranks of those who encourage less fat in the diet.

In a recent announcement, the U.S. surgeon general named overconsumption of fat as the No. 1 dietary problem in the United States. These guidelines are based on research that relates high-fat diets to a variety of medical problems, such as heart disease and cancer. Apparently, Americans have been listening to these health professionals because the average intake of fat in the United States is now about 37 percent of total calories, a drop of about 5 percent in the past decade. Most health professionals advise a further decrease in fat intake to less than 30 percent of total calories, with saturated fat providing no more than 10 percent.

Although we get fats from many different foods, saturated fats are found primarily in animal products such as red meats, poultry and fish, milk and milk products, and eggs. Vegetable fat is consumed mostly in the form of plant oils such as soybean, corn, sunflower, safflower, canola, cottonseed, palm and coconut.

Although most vegetable fats are unsaturated, palm and coconut are more like animal fats. The difference between saturated and unsaturated fats has to do with the chemical structure of the fat.

Saturated fats have hydrogen on each of the carbons that make the backbone of the structure. In other words, all of the carbons are "saturated." If one carbon molecule has no hydrogen, the fat is called a monosaturated fat (e.g., olive oil, peanut oil). If more than one carbon is free of hydrogens, the fat is a polyunsaturated fat (e.g., corn oil, safflower oil).

Sometimes manufacturers use a process called hydrogenation (adding hydrogen to the structure) to make the fat more stable. Peanut butter, shortening and margarine are often treated this way. However, by adding hydrogen, the number of saturated fatty acids is increased and the chance of it doing harm to the body is greater.

Next week, I will discuss some ways to decrease the total amount of fat and the amount of saturated fat in the diet.