Chapter 4 – The Lipids: Fats and Oils

Chapter 4 Summary

A Primer on Fats

Lipids in the body function to maintain the health of the skin and hair; to protect body organs from heat, cold, and mechanical shock; and to provide a continuous energy supply. The breakdown of 1 pound of body fat supplies 3,500 calories to meet energy needs. In foods, fats and oils act as a solvent for the fat-soluble vitamins and the compounds that give foods their flavors and aromas.

A Closer View of Fats

About 95% of the lipids in the diet are triglycerides; the phospholipids and sterols make up the other 5%. The fatty acids may be classified as saturated, monounsaturated, or polyunsaturated. Many combinations of fatty acids are possible in fats and oils.

Linoleic acid (an omega-6 fatty acid) and linolenic acid (an omega-3 fatty acid) are the most important of the polyunsaturated fatty acids in foods. The body is unable to synthesize them; therefore, they are essential fatty acids. Deficiency symptoms of the essential fatty acids include skin rash, and in children, poor growth.

Characteristics of Fats in Foods

Food fats containing unsaturated fatty acids spoil easily. Hydrogenation makes these acids less susceptible to spoilage; but in partial hydrogenation, trans-fatty acids, which may have an adverse effect on health, are formed.

The Other Members of the Lipid Family: Phospholipids and Sterols

Phospholipids and a related molecule called lecithin are molecules consisting of fats (fatty acids) combined with a phosphate atom. These molecules are used to build the walls of all of the cells in our bodies. Additionally, they serve as emulsifiers that allow fat to be transported back and forth through the cell membrane.

Sterols are fats that have been changed or altered within the body to perform certain functions. Perhaps the best known sterol is cholesterol, found in the blood (as a fat transporter) and in the cell walls. It is also the major constituent of bile, a substance stored in the gallbladder that helps break down fats in the small intestine. Cholesterol is also found in the skin as a precursor of vitamin D. Yet another use of sterols is in the production of the sex hormones (estrogen and testosterone).

How the Body Handles Fat

During digestion, the triglycerides are emulsified by bile and then broken apart by enzymes to monoglycerides, glycerol, and fatty acids, which then pass into the intestinal cells. After absorption, all three classes of lipids are transported by lipoproteins in the body fluids.

“Good” versus “Bad” Cholesterol

Cholesterol is made in the body by the liver. Most of this cholesterol becomes bile, used to emulsify fats. Cholesterol from the liver may be transported to body tissues by LDL-cholesterol and my also be abnormally deposited in artery walls. A diet high in saturated fat and cholesterol has been implicated as a causative factor in heart disease. Authorities recommend that you choose a diet that is low in saturated fat and cholesterol and moderate in total fat as a preventive measure:

  • Keep fat intake within 20-35% of total calories.
  • Eat no more than 10% of calories as saturated fat.
  • Limit daily cholesterol intake to no more than 300 milligrams.

Fat in the Diet

Foods that contain fat are found in the meat and milk groups and in fats themselves. Most of the saturated fat found in the diet comes from meat and other animal fats. Organ meats, shellfish, eggs, meats, and other animal fats contribute cholesterol to the diet. No plant product contains cholesterol. Vegetable and fish oils generally contain more polyunsaturated fats than do other animal fats. The Mediterranean diet is rich in fruits, vegetables, grains, fish, and beans and naturally low in saturated fat because little meat and butter is consumed. The present boom in both low-fat and fat-free products has to do with the country’s expanding health consciousness. Manufacturers use several techniques to replace the fat in their products, including the development of fat substitutes such as Simplesse and Olestra.

Diet and Heart Disease

The Spotlight considers the relationship between nutrition and heart disease. The chapter concludes with guidance for a heart-healthy lifestyle:

  • Achieve an overall healthy eating pattern. Consume a variety of fruits, vegetables, and grain products, including whole grains; include low-fat milk products, fish legumes, poultry, and lean meats.
  • Achieve a healthy body weight.
  • Achieve a desirable cholesterol level.
  • Achieve a desirable blood pressure level.