Food and nutrition.pdf

Nutrients 57materials called lipids. Lipids are those constituents of plants or animalswhich are insoluble in water but soluble in other organic solvents.Amongst the various foodstuffs, fats provide the body with maximumenergy (9 kcal per gram), approximately twice that for an equal amountof protein or carbohydrates.Lipids are concentrated sources of energy as well as structuralcomponents of cell membranes. Everybody needs a certain amount ofdietary fat for normal body functions. When fats are digested, emulsified,and absorbed, they facilitate the intestinal absorptioh and transport of fatsoluble vitamins A, D, E, and K. They are also used to cushion and protectthe heart, kidneys and liver. In certain climates subcutaneous body fathelps to insulate the body from the cold and prevent heat loss throughthe skin. These functions can be met by a daily intake of 15 to 25 grams offat.Lipids enter the body through the mouth and pass to the- stomach,but are little affected by its acidic environment. They are absorbedprimarily in the small intestines, where they are emulsified by salts of thebile acids and are hydrolyzed to fatty acids and glycerol by various watersolubleenzymes (lipases). From the intestines, the hydrolyzed lipids enterthe bloodstream and are transported to other organs, mainly the liver, forfurther metabolism. Ultimately the fatty acids may be degraded to carbondioxide and water to furnish energy.There are many types of fatty acids, but they can be grouped intothree divisions - saturated fats, monounsaturated fats and polyunsaturatedfats. Polyunsaturated fats consist of two classes, omega-3 and omega-6.Saturated fats have a profound hypercholesterolemic (increase bloodcholesterol levels) effect. They are found predominantly in animalproducts (butter, cheese and meat) but coconut oil and palm oil arecommon vegetable sources. Saturated fat raises blood cholesterol levelsmore than anything else in the diet, even more than dietary cholesterol.Intake of monounsaturated fats in oils such as olive oil is thought tobe preferable to consumption of polyunsaturated fats in oils such as comoil because the monounsaturated fats apparently do not lower highdensity-lipoprotein(HDL) cholesterol levels. Evidence for this belief isderived primarily from metabolic ward studies of relatively shortduration. -Unsaturated fats come primarily from vegetable oils (safflower, com,soyabean, cottonseed, sesame, and sunflower oils), nuts and seeds,although fish is a good source of unsaturated fatty acids. Most of theessential fatty acids are found in unsaturated fat, so foods high in saturatedfat and cholesterol (animal fat, dairy products and eggs) should be eatensparingly.