Unit 5
Lipids: Fats, Oils, Phospholipids, and Sterols

Dietary lipids have gained much attention over the years because of growing evidence of their association with chronic lifestyle diseases, such as heart disease, cancer, and obesity. However, dietary lipids do have an essential role in nutrition. They provide the most concentrated form of energy (nine kcalories per gram of fat), and are the source of essential fatty acids. As with other nutrients, their overconsumption will result in adverse health effects. In our affluent society, people consume too much fat, especially processed and saturated fats.

In this unit, we examine the chemical and physical characteristics of various types of lipids and discuss their sources. We study the processes of digestion, absorption, and transport of lipids. We review the functions of lipids and the effects of diet on blood cholesterol. Finally, we look at the present trends in fat consumption by Canadians, the current recommendations for fat intake, and the effects of food processing on dietary lipids.

This unit consists of four sections:

5.1—Chemistry and Classification
5.2—Digestion, Absorption, and Transport
5.3—Functions and Health Effects
5.4—Lipids in the Diet

Objectives

After completing this unit you should be able to

  1. identify the chemical characteristics of the three main categories of lipids—triglycerides, phospholipids, and sterols—and give examples of their food sources.
  2. name the classifications of fatty acids based on the chemical characteristics of chain length and degree of unsaturation; relate these chemical characteristics to the physical properties of fats and oils; and give examples of saturated, monounsaturated, and polyunsaturated fats.
  3. describe the physical effects and nutritional implications of hydrogenation and oxidation of dietary fats.
  4. identify the two families of essential fatty acids, identify their “parent” fatty acids, and give examples of dietary sources.
  5. outline the steps in the digestion of lipids, identifying the sites, the substrates, the enzymes, and the products of digestion; describe the mechanism of lipid absorption for various types of lipids.
  6. describe the transport of lipids in the body, and discuss the significance of the different lipoproteins in cardiovascular disease.
  7. describe the roles of fat in the body.
  8. discuss the effects of diet on blood cholesterol levels, and the implication of high blood cholesterol for cardiovascular disease.
  9. describe a heart-healthy diet and give examples of suitable food choices in such a diet.
  10. list and describe the nutritional roles of essential fatty acids—EPA and DHA—and identify the causes and health effects of essential fatty acid deficiency.
  11. describe the pattern of fat consumption in Canada, and discuss the implication of lipid consumption on health.
  12. state the current recommendations for fat consumption and describe the food pattern outlined in Canada’s Food Guide which achieves these recommendations.
  13. identify dietary sources of SFA, MUFA, PUFA, EPA, and DHA.