Dietary Sources and Intakes

The major sources of carbohydrates are cereals, accounting for over 50% of carbohydrate consumed in both developed and developing countries, followed by sweeteners, root crops, pulses, vegetables, fruit, and milk products. Carbohydrate and nutrient intake in general can be estimated using data from food production and balance sheets, household surveys, and individual assessments (Table 1). Figure 1 shows the trends in carbohydrate consumption by food group as a percentage of total carbohydrate in developed and developing countries, obtained from food balance data in 1994.

Sugars

The term 'sugar' includes monosaccharides and dis-accharides. The most common monosaccharides are glucose (or dextrose), fructose, and galactose. Glucose is found in fruit, honey, maple syrup, and vegetables. Glucose is also formed from sucrose hydrolysis in honey, maple syrup and invert sugar, and from starch hydrolysis in corn syrups. The properties of glucose are important for improving food texture, flavor, and palatability. Glucose is the major cell fuel and the principal energy source for the brain. Fructose is found in honey, maple sugar, fruit, and vegetables. Fructose is also formed from sucrose hydrolysis in honey, maple syrup, and invert sugar. It is commonly used as a sweetener in soft drinks, bakery products, and candy in the form of high-fructose corn syrups. Galactose is found primarily in milk and dairy products.

The most common disaccharides are sucrose, lactose, and maltose. Sucrose is mostly found in sugar cane and beet, and in lesser amounts in honey, maple sugar, fruit, and vegetables. The properties of sucrose are important in improving viscosity, sweetness, and flavor of baked foods, ice cream, and desserts. Maltose is formed from starch digestion. It is also produced from the germination of grain for malt liquors. Lactose is found in milk and dairy products, and is not as sweet as glucose or sucrose.

In the second part of the twentieth century, sugar intake increased markedly in the US, because of increased consumption of added sugars in beverages and foods. According to the US Food Supply Data, consumption of added sugars has increased from 27 teaspoons/person/day in 1970 to 32 teaspoons/ person/day in 1996, which represents a 23% increase. Soft drinks are the most frequently used form of added sugars, and account for one-third of total sugar intake. In Europe the trend of sugar consumption has been a steady one.

Table 1 Approaches for determination of trends in nutrient consumption worldwide

Approach

Advantages

Disadvantages

Food production

Food balance sheets Household surveys

Individual assessments

Figures available for every crop

Figures available for every food item Figures close to actual food consumption

Figures close to actual food consumption

Affected by agricultural practices, weather conditions, external forces Inadequate to determine food waste and spoilage Inadequate to determine food consumption outside the home, food waste, and spoilage Data not available for all countries Diverse methods of assessment

re o

80 70 60 50 40 30 20 10 0

1

1 n« r^ ri rL

□ Developed countries ■ Developing countries

□ Developed countries ■ Developing countries

Figure 1 Trends in energy consumption by carbohydrate food group as a percentage of total carbohydrate in developed and developing countries, obtained from food balance data in 1994. Data obtained from FAO/WHO (1998). Carbohydrates in human nutrition. Report of a joint FAO/WHO expert consultation. FAO Food and Nutrition Papers 19 66: 1-140.

Polysaccharides

Starch Starch is the most important and abundant food polysaccharide. Starch is predominantly derived from plant seed, such as wheat, maize, rice, oats, and rye, and from plant roots, such as potatoes. Legumes and vegetables also contribute to the starch content of the diet. Bread and pasta are popular forms of starch, while tropical starchy foods, such as plantains, cassava, sweet potatoes, and yams are increasingly contributing to carbohydrate intake. Starch accounts for 20-50% of total energy intake, depending on the total carbohydrate consumption.

Nonstarch Nonstarch polysaccharides (NSP), formerly referred to as 'dietary fiber,' can either be soluble or insoluble and are mainly derived from cereals, especially wholegrain. Wheat, rice, and maize contain predominantly insoluble NSP, while oats, rye, and barley contain predominantly soluble NSP. Vegetables are also a source of NSP and contain equal amounts of insoluble and soluble NSP. Intakes of NSP range from about 19 g day-1 in Europe and North American countries to 30gday-1 in rural Africa.

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