Physical Values

The energy values of a single food or nutrient can be directly measured by determining the amount of heat released upon its ignition and total combustion in a bomb calorimeter (Fig. 1). The values obtained with this direct measurement for different foods and nutrients are reported in Table 1 [3].

These values do not correspond to the amount of energy utilisable by the body, since they do not take into consideration the amount lost by digestive and metabolic processes, i.e. excretion in the faeces, sweat, and urine.

Fig. 1.1 Schematic representation of a bomb calorimeter. A weighted portion of dried food, placed on a platinum plat (A), is ignited and burned by electrical wires (electrodes E) under oxygen pressure. From the increase of water temperature, it is possible to calculate how much heat has been released

Fig. 1.1 Schematic representation of a bomb calorimeter. A weighted portion of dried food, placed on a platinum plat (A), is ignited and burned by electrical wires (electrodes E) under oxygen pressure. From the increase of water temperature, it is possible to calculate how much heat has been released

Table 1. Physical energy values of common foods and nutrients (Data from [3])

Food or nutrient

Kcal/g

KJ/g

Starch

4.18

17.49

Glycogen

4.19

17.53

Dextrins

4.11

17.20

Disaccharides

3.95

16.53

Monosaccharides

3.74

15.65

Glycerol

4.31

18.03

Butyric acid

5.95

24.89

Oleic acid

9.41

39.37

Stearic acid

9.53

39.87

Butter

9.20

38.49

Olive oil

9.33

39.04

Rapeseed oil

9.49

39.71

Peanuts oil

9.47

39.62

Beef tallow

9.50

39.75

Lard

9.59

40.12

Caseine

5.86

24.52

Gelatine

5.25

21.97

Ovoalbumine

5.69

23.81

Wheat Gluten

5.95

24.89

Ethanol

7.11

29.75

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