Fats and Oils

I

Introduction

Fats and Oils, group of naturally occurring organic compounds called triglycerides—esters comprised of three molecules of fatty acids and one molecule of the alcohol gylcerol. They are oily, greasy, or waxy substances that, in their pure state, are normally tasteless, colorless, and odorless. Fats and oils are lighter than water and are insoluble in it; they are slightly soluble in alcohol and are readily dissolved in ether and other organic solvents. Fats are soft and greasy at ordinary temperatures, whereas fixed oils—as distinct from essential oils and petroleum—are liquid. Some waxes, which are hard solids at ordinary temperatures, are chemically similar to fats (see Wax).

II

Nature and Uses of Fats

The fats normally occur in animal and vegetable tissue as a mixture of several pure fats plus free fatty acids. The most common of such fats are palmitin, the ester of palmitic acid; stearin, the ester of stearic acid; and olein, the ester of oleic acid. These pure chemical compounds are contained in different proportions in various natural fats and oils, and they determine the physical characteristics of each of these substances.

Fats are designated as saturated or unsaturated, depending on whether the chemical bonds between the carbon atoms of the fat molecules contain all the hydrogen atoms they are capable of holding (saturated) or have capacity for additional hydrogen atoms (unsaturated). Saturated fats generally are solid at room temperature; unsaturated and polyunsaturated fats are liquids. Unsaturated fats may be converted to saturated fats by adding hydrogen atoms in a process known as hydrogenation. This process creates saturated fats called trans-fatty acids.

Vegetable fats are usually obtained by pressure extraction from seeds and fruit. Animal fats are often extracted from animal tissue by boiling fat-containing tissue in water and then allowing it to cool. The heat melts the fat out of the tissue; it then rises to the surface of the water because of its low specific gravity and can be skimmed off.

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The largest consumption of fats and oils is in the form of food. Certain natural fats, such as butter fat and lard, are used as food with little or no preparation. Certain unsaturated oils, such as cottonseed and peanut oils, are often partly hydrogenated to increase their melting points and make them suitable for use as shortening and cooking fats. Tallow, the animal fats and oils from sheep and cattle, is used for candlemaking and in margarine. Natural oils that contain esters of unsaturated acids are known as drying oils and possess the property of forming a permanent dry film when exposed to air. Linseed oil and other oils of this type are extensively used in the production of paints. Fats also serve as a raw material in the manufacture of soap.

III

Animal Fats

Living cells contain both simple fats, described above, and other fatlike materials. The latter, which are more complex substances, include lipids and sterols. The so-called phospholipids are derivatives of fatty acids, glycerol, phosphoric acid, and nitrogen-containing bases. The glycolipids do not contain phosphorus but are derived from carbohydrates, fatty acids, and nitrogen compounds. Sterols are composed of complicated molecules, each containing 20 or more carbon atoms in an interlocking or fused ring structure.

The fats seem to provide a concentrated, efficient source of energy for the cells. The oxidation of a gram of typical fat releases 9300 calories of energy. In contrast, the oxidation of a gram of protein or carbohydrate yields only 4100 calories. Fats also tend to stiffen the cells because they form a semisolid mixture with water.

IV

Physiological Effects

Research focusing on heart disease and other circulatory disorders indicates that excessive consumption of foods high in certain fats, including lipids and sterols, increases the risk of developing these diseases. U.S. studies show that as much as 50 percent of the caloric intake in a modern diet consists of fats. Other studies demonstrate that the likelihood of heart disease decreases when the intake of saturated fats is reduced (see Artery; Heart: Heart Diseases; Nutrition, Human). Recent research indicates that excessive consumption of trans fats, such as those produced in the hydrogenation of vegetable oil to make margarine, may also increase the risk of heart disease.

When saturated solid fats are added to the diet, the amount of cholesterol in the blood increases, but when liquid, unsaturated fats or oils (particularly the polyunsaturated type) replace solid fat, the amount of cholesterol decreases. High cholesterol levels in the blood appear to promote the deposition of hard, fatty materials in the arteries, causing the arteries eventually to clog. When the coronary artery around the heart becomes clogged in this manner, blood supply to the heart is interrupted and a heart attack occurs. The American Heart Association recommends restricting the total fats in a diet, reducing the consumption of cholesterol-rich foods, such as milk and butter, replacing saturated fats with unsaturated fats, and limiting the intake of trans fats. Scientists are continuing to seek a thorough understanding of how the body handles fatty materials and why cholesterol levels rise to the point that fat is deposited on artery walls.

Other research indicates that some types of fats in the diet have beneficial health benefits. Particular attention has focused on omega-3 fatty acids, which appear to be essential to human health. These polyunsaturated fatty acids cannot be manufactured by the body itself and must come from food. Studies suggest that omega-3 fatty acids may help reduce inflammation and may reduce risk factors associated with heart disease, stroke, cancer, and arthritis. Omega-3 fatty acids also appear to play important roles in brain function, including memory, cognitive skills, and behavior. Important sources of omega-3 fatty acids include oil-rich fish such as salmon, tuna, and sardines; flax seeds; whole grains; walnuts; and dark, leafy green vegetables. Fish-oil supplements are also high in omega-3 fatty acids. Some nutritionists have expressed concerns that modern diets are typically low in omega-3 fatty acids, a deficiency that may be contributing to a variety of health problems.

For individual oils, see Castor Oil and articles on the various plants, such as cotton, flax, and olive.

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