Unit 6
Protein: Amino Acids

Protein (Greek proteios, “of prime importance”) was the first substance recognized as vital to cells. Proteins have therefore been highly regarded, being seen as supplying strength and power to the body.

Protein is, of course, an important nutrient required by all the body cells. Proteins are constituents of muscle tissues, soft tissues, bones, teeth, blood and other body fluids, and enzymes. However, dietary proteins are often overemphasized and treated as nutrients with fantastic properties, especially for muscle building.

This unit provides an overview of proteins: their chemical characteristics, the processes of protein digestion and absorption, and protein quality. We examine the functions of proteins in the body, the health effects of protein deficiency or excess, and the issue of vegetarianism. Finally, we look at the patterns of protein consumption and the recommendations for intake.

This unit consists of four sections:

6.1—Chemistry
6.2—Digestion, Absorption, and Protein Quality
6.3—Functions and Health Effects
6.4—Proteins in the Diet

Objectives

After completing this unit, you should be able to

  1. define amino acid, and identify the chemical groups that are common in all amino acids.
  2. describe the basic chemical formation of proteins.
  3. define denaturation, and describe the effect of denaturation on the physical and physiological properties of proteins.
  4. outline the steps in the digestion of proteins, and briefly describe how the products of protein digestion are absorbed by the body.
  5. distinguish between essential, non-essential, and conditionally essential amino acids.
  6. list and describe the factors that determine protein quality, and define complete protein, incomplete protein, limiting amino acid, and complementary protein, giving examples of each.
  7. identify the three general categories of protein functions, and give examples of each.
  8. explain the concept of nitrogen balance; define nitrogen equilibrium, positive nitrogen balance, and negative nitrogen balance; and describe examples of each of these states of nitrogen balance.
  9. identify some health effects of protein deficiency and protein excess.
  10. differentiate among the three major types of vegetarian diets—lactovegetarian, lacto-ovo vegetarian, and vegan—and discuss the health benefits of the vegetarian way of eating.
  11. discuss the possible nutritional concerns posed by vegetarianism, and suggest ways to overcome them.
  12. identify the factors considered when establishing the RDA for protein, and state the current recommendations and the RDA for dietary protein for adults.
  13. describe the patterns of protein consumption in Canadians.