Carbohydrate as a nutrient
Carbohydrate has many important functions as a nutrient:
• It provides energy. One gram of carbohydrate in the form of starch or sugars provides 3.75kcal (16kJ). For the purposes of food labelling, a conversion factor of 4kcal (17kJ) is used. It has recently been agreed by the European Commission that dietary fibre also makes a small contribution to energy as it is digested in the large bowel by the resident bacteria. An energy value of 2kcal/g (8.4kJ) has been attributed to dietary fibre.
• The body’s tissues require a constant supply of glucose, which is used as a fuel. The main source of glucose is dietary carbohydrate but it can also be synthesised from protein. If the diet is low in carbohydrate, a greater percentage of dietary protein is used to provide glucose, which means less is available for the growth and repair of body tissues. Thus, carbohydrate in the diet has a protein-sparing effect.
• Most foods contain some carbohydrate. Table 1 shows a selection of foods that contain carbohydrate, listing their sugars, starch and fibre content.
Table 1. Carbohydrate content of selected foods (per 100g)
|Food (per 100g)||Energy value Kcal/KJ||Carbohydrate (g)||Sugars (g)||Starch (g)||Fibre (AOAC) (g)|
|Brown rice, boiled||132/562||29.2||0.1||29.0||1.5|
|Spaghetti, white, cooked||141/601||31.5||1.0||30.5||1.7|
|Spaghetti, wholemeal, cooked||134/569||27.5||Tr||27.5||4.2|
|Baked potato (with skin)||97/413||22.6||1.4||21.2||2.6|
|Lentils, red, cooked||100/424||17.5||0.8||16.2||2.5|
Carbohydrates in the diet
The National Diet and Nutrition survey of UK adults found the average daily intake of carbohydrate was 252g for men and 198g for women, representing 47.5% and 48.3% of food energy intake for men and women, respectively. As shown in Figure 2, cereal and cereal products were the main source of carbohydrate for adults in Britain (including 20% of carbohydrate in the form of bread).
The contribution of different foods to the average daily non-milk extrinsic sugars (NMES) intake in British adults is shown in Table 2. Intake of NMES exceeded the dietary reference value of 11% of dietary energy in all age groups and was highest in children and in elderly people in institutions. The average NMES intake in men was 12.8% of food energy, while in women NMES contributed 11.8% of food energy. Among children, NMES contributed, on average, 15.1% and 14.7% of food energy for boys and girls, respectively.
Table 2: Percentage contribution of food types to average daily non-milk extrinsic sugar intake of British adults.
|Food/drink type||% contribution to average daily NMES intake|
|Sugars, preserves and confectionery||27%|
|Cereal and cereal products||20%|
|Milk and milk products||6%|