Unit 4
Carbohydrates: Sugar, Starch, and Fibre

Carbohydrates are the most abundant and readily available nutrient in foods. Intakes vary with cultural and economic factors, ranging from about 45–50% of energy consumption in the diets of people in affluent Western countries, to as high as 80% in diets of people in some developing countries.

The most important function of carbohydrates is to supply energy to the body. Pure carbohydrates, such as sugar and starch, provide the same amount of energy to the body as protein: four kcalories per gram, while fat provides nine kcalories per gram. Many food sources of complex carbohydrates are also rich in protein, vitamins, and minerals. Most types of dietary fibre, which are associated with many health benefits, are also carbohydrates.

In this unit, we examine the chemical composition and classification of carbohydrates and give examples of food sources of each type. We review the processes of digestion and absorption of carbohydrates, relating them to the problem of lactose intolerance. We then discuss the functions of carbohydrates, the health effects of dietary fibre, and the regulation of blood glucose. Finally, we look at the trends in carbohydrate consumption and the Canadian recommendations for carbohydrate intake.

This unit consists of five sections:

4.1—Chemistry and Classification
4.2—Digestion and Absorption
4.3—Functions of Carbohydrates
4.4—Regulation of Blood Glucose
4.5—Carbohydrates in the Diet

Objectives

After completing this unit you should be able to

  1. define carbohydrate, and identify the basic chemical components of carbohydrates.
  2. identify and describe the simple carbohydrates (monosaccharides and disaccharides) and complex carbohydrates (glycogen, starch, and fibre); and give examples of food sources for each type of fibre.
  3. outline the steps of carbohydrate digestion by identifying the sites of carbohydrate digestion, the substrates, the enzymes, and the products of digestion; and identify the mechanisms used in the absorption of carbohydrates.
  4. define lactose intolerance, describe its symptoms, and describe dietary management to control lactose intake.
  5. list and describe the functions of carbohydrates in the body.
  6. describe how the the body maintains and regulates its blood glucose level by the action of specific hormones.
  7. describe recent trends in carbohydrate consumption in Canada.
  8. discuss the health effects of excessive sugar intake and the recommendations for sugar intake.
  9. discuss the health benefits of dietary fibre and and recommendations for dietary fibre intake.