Energy Values from the Food Composition Tables

These values represent the average calculations derived from the chemical composition of food, which can vary according to the sample and the method used, resulting in possible differences among the various tables applied by different countries. However, the differences are generally small and acceptable for evaluating the actual intake of food energy in a mixed diet.

For carbohydrates, a value of 3.75 Kcal/g, when expressed as monosaccharides (corresponding to the physical value), is used. In the case of disac-charides, because the molecular weight of a monosaccharide is higher than that of a disaccha-ride molecule, a factor of 1.05 is applied and the energy value is 3.75 x 1.05 = 3.94 Kcal/g. In the case of starch, the factor is 1.10 and the energy value is 4.125 Kcal/g [8].

Together, the monosaccharides + disaccharides + starch represent the available carbohydrates. Cellulose, hemicellulose, pectin, gums, and resistant starch* (collectively referred to as dietary

* Resistant starch is the portion of starch that cannot be digested by human enzymatic activities or absorbed in the digestive tract. Generally it represents a small percentage of total starch (1-3%). The resistance to digestion can be due to physical inaccessibility (as in cereals and grain kernels that are whole or only partially minced) or to the absence of gelatinisation (green bananas, or uncooked potatoes) or to starch 'retrogradation' (as in bread, food cooked at elevated temperatures, corn flakes, or biscuits).

fibre or unavailable carbohydrates) are not considered to have energetic value. However, unavailable, unaltered carbohydrates reach the colon, where they can be fermented by the local microflora, which consist of several genera of anaerobic microorganisms. These utilise dietary fibre to produce pyruvic acid, an important metabolic intermediate from which short-chain fatty acids (SCFA), i.e. acetic, propionic, and butyric acids, and other gases are produced (Fig. 2) [9].

Since the SCFA, produced at an estimated average amount of 380 mmol/day, can be absorbed in the intestinal mucosa and metabolised to yield energy, an energetic value for dietary fibre of 1.5 Kcal/g can be calculated [10].

In practice, however, since dietary fibre reduces the absorption of other energetic nutrients and increases faecal mass, its contribution to the total energetic value of foods in a mixed diet is not considered. The same is true for organic acids, because of their presence in minimal amounts in foods and their low specific energy value (2 Kcal/g).

On the basis of the values reported in the Food Composition Tables, foods can be grouped into four main classes: (1) energy-dense foods, (2) high-energy foods, (3) moderate-energy foods, (4) low-energy foods. The first category comprises foods with energy values between 900 and 500 Kcal/100 g of edible part; the second category consists of foods with energy values between 500 and 300 Kcal/100 g; in the third category are foods with energy values between 300 and 100 Kcal/100 g; and in the fourth category are foods with energy values from 80 to 10 Kcal/100 g.

The most common foods in the four classes are listed in Table 2 [8].

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