Fats (or lipids) are the most concentrated source of energy in the diet. When oxidized, fats provide more than twice the number of calories per gram than proteins or carbohydrates. One gram of fat provides 9 calories to the body. Protein and carbohydrates only provide 4 calories.
In addition to providing energy, fats also act as carriers for the fat-soluble vitamins A, D, E and K. By aiding in the absorption of vitamin D, fats help make calcium available to body tissues, particularly to the bones and teeth. Fats are also important for the conversion of carotene, such as beta carotene to vitamin A.
Fats prolong the process of digestion by slowing down the stomach’s secretions of hydrochloric acid. Thus, fats create a longer lasting sensation of fullness after a meal.
Fats are broken down into four types of fatty acids: saturated, monounsaturated, polyunsaturated and trans-fatty acids:
Saturated fats are fats that are solid at room temperature (i.e., beef fat, lard, chicken fat). They have also been shown to raise cholesterol and contribute to heart disease.
Monounsaturated fats are almost solely from oleic acid, a non-essential fatty acid. These fats have no effect on cholesterol levels. Olive oil has 75% Oleic acid.
Polyunsaturated fats cannot be made by the body. Therefore they must be obtained from dietary sources. They are essential as hormone precursors as well as components of cell membranes. Both mono and polyunsaturated fats are usually liquid at room temperature. They are derived from vegetable, nut or seed sources (corn, sunflowers, safflowers and olives).
Trans-fatty acids are produced when unsaturated fatty acids are hydrogenated. Hydrogenation is done by food manufacturers to help foods stay fresh on the shelf or to get a solid fat product like margarine. These fats are not essential and can raise bad cholesterol while lowering good cholesterol. These fats should be avoided if possible.
The American Heart Association’s nutrition committee strongly advises that healthy Americans over age two limit the fat they eat. Specifically, they should limit their intake of saturated fat to less than 10 percent of total calories. Total fat intake should be less than 30 percent of total calories. This is another reason why popular low carb diets can be very unhealthy. The current popular low carb diets average 50-70% fat! If people limit their daily intake of fats and oils to about 5-8 teaspoons, they aren’t likely to get an excess of trans fatty acids.