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  Information on Lipids

Fats, oils, and waxes belong to the group of naturally occuring organic materials called lipids. Lipids are those constituents of plants or animals which are insoluble in water but soluble in other organic solvents.

Amongst the various foodstuffs, fats provide the body with maximum energy (9 kcal per gram), approximately twice that for an equal amount of protein or carbohydrates.

Lipids are concentrated sources of energy as well as structural components of cell membranes. Everybody needs a certain amount of dietary fat for normal body functions. When fats are digested, emulsified, and absorbed, they facilitate the intestinal absorption and transport of fat soluble vitamins A, D, E, and K. They are also used to cushion and protect the heart, kidneys and liver. In certain climates subcutaneous body fat helps to insulate the body from the cold and prevent heat loss through the skin. These functions can be met by a daily intake of 15 to 25 grams of fat.

Lipids enter the body through the mouth and pass to the stomach, but are little affected by its acidic environment. They are absorbed primarily in the small intestines, where they are emulsified by salts of the bile acids and are hydrolyzed to fatty acids and glycerol by various water-soluble enzymes (lipases). From the intestines, the hydrolyzed lipids enter the bloodstream and are transported to other organs, mainly the liver, for further metabolism. Ultimately the fatty acids may be degraded to carbon dioxide and water to furnish energy.

There are many types of fatty acids, but they can be grouped into three divisions - saturated fats, monounsaturated fats and polyunsaturated fats. Polyunsaturated fats consist of two classes, omega-3 and omega-6.

Saturated fats have a profound hypercholesterolemic (increase blood cholesterol levels) effect. They are found predominantly in animal products (butter, cheese and meat) but coconut oil and palm oil are common vegetable sources. Saturated fat raises blood cholesterol levels more than anything else in the diet, even more than dietary cholesterol.

Intake of monounsaturated fats in oils such as olive oil is thought to be preferable to consumption of polyunsaturated fats in oils such as corn oil because the monounsaturated fats apparently do not lower high-density-lipoprotein (HDL) cholesterol levels. Evidence for this belief is derived primarily from metabolic ward studies of relatively short duration. [Dreon, D.M., Vranizan, K.M., Krauss, R.M., Austin, M.A., and Wood, P.D., The effects of polyunsaturated fat vs monounsaturated fat on plasma lipoproteins, Journal Of The American Medical Association, 263:2462, 1990]

Unsaturated fats come primarily from vegetable oils (safflower, corn, soyabean, cottonseed, sesame, and sunflower oils), nuts and seeds, although fish is a good source of unsaturated fatty acids. Most of the essential fatty acids are found in unsaturated fat, so foods high in saturated fat and cholesterol (animal fat, dairy products and eggs) should be eaten sparingly.

Fats should make up only 10 to 25 percent of the calories (not weight) in your diet. There is an overwhelming consumption of fats in the average Western Diet, this has lead to a huge health problem among population groups with a diet high in animal fats (ice-cream, chocolates, fast foods and desserts). There are many diet related human disorders that are found almost exclusively in the Western World, Coronary Heart Disease (CHD) and cancer of the colon, are a few of the more severe.

Cholesterol
Cholesteryl esters are composed of a single fatty acid esterfied to cholesterol, in which the polar component is an alcohol.

Cholesterol is a major component of all cell membranes. It is required for synthesis of sex hormones, bile acids, and vitamin D. It is also a precursor of the steroid hormones produced by the adrenal cortex and gonads.

Dietary cholesterol is found only in foods derived from animals (meat, fish, poultry, eggs and dairy products); it is not present in plants.

Table 1.2 - Sources of dietary cholesterol