Fat

Fat, compound of carbon, hydrogen, and oxygen found in certain parts of the body, an important constituent of diet. Fat is the most concentrated source of food energy, supplying 9 calories per gram; protein and carbohydrate, the other 2 sources of food energy, supply only 4 calories per gram. Fats are the chief sources of essential fatty acids (EFAs), as well as carriers of vitamins A, D, E, and K. Three molecules of fatty acid combined with one molecule of glycerol constitute 1 molecule of fat, the chemical name of which is a triglyceride. A fatty acid is saturated if its chain of carbon atoms contains all the hydrogen it can hold, or if there are no double bonds between carbon atoms. Saturated fats are usually solid at room temperature; they occur in both animal and vegetable fats, but chiefly in the former. A fatty acid is unsaturated if its chain of carbon atoms has 1 or more double bonds where hydrogen could be added. The process of adding hydrogen to a double bond in an unsaturated fatty acid to make it more saturated is called hydrogenation. Monounsaturated fatty acids have only 1 double bond where hydrogen could be added. Polyunsaturated fatty acids have 2 or more double bonds where hydrogen could be added. Polyunsaturated fats are usually oils and are most abundant in plant and fish oils. Nearly all fats from plant sources are unsaturated; the only major exception is palm (or coconut) oil, which is highly saturated. The utilization of fat in humans is affected diet and state of nutrition, the endocrine system, degree of activity, age, heredity, and diseases that may interfere with the absorption and metabolism of fat. Diets high in fat can lead to above-normal amounts of lipids (triglycerides, fatty acids, cholesterol, and other fat-like substances) in the blood, associated with atherosclerosis. Changes in dietary habits to reduce the risk of coronary heart disease in later life include adjusting caloric intake to maintain an optimum weight, reducing fat intake so that fat supplies less than 35% of the total number of calories (of which less than 10% should be from saturated fats and up to 90% from polyunsaturated fats, with the remainder supplied by monounsaturated fats) and limiting the daily intake of cholesterol to fewer than 10.6 oz (300 mg).