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 per cent of energy consumption in the diets of affluent Western countries, to as high as 80 per cent in diets of 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 the six sections listed below.

• Section 4.1  Chemistry and Classification
• Section 4.2  Digestion and Absorption
• Section 4.3  Functions of Carbohydrates
• Section 4.4  Regulation of Blood Glucose
• Section 4.5  Dietary Fibre
• Section 4.6  Carbohydrates in the Diet