From a nutrition perspective, the energy content of a food is an important parameter. It is of particular interest to consumers who are aware that their lifestyles make them prone to diseases like obesity and diabetes. They may have been advised to reduce energy intakes, especially by purchasing food products labeled as "reduced in calorie," "low in calorie," or "light." It is necessary for manufactures to have the correct energy values for the different food components in such labeled food products. In many countries, information on the energy provided by a particular food product is required, as is the information on the composition of the various nutrients it provides. Such information is mandatory on prepackaged food products in the U.S., but in the European Union (EU) only certain nutrition claims require this labeling.
The energy content of a food product equals the amount (in grams) of each component or group of components (i.e., carbohydrates, protein, fat, dietary fiber, and polyols, etc.) multiplied by their respective energy conversion factors (that are eventually specified in laws or directives) and totalling these amounts. These conversion factors are expressed in kilocalories per gram (kcal/g) or kilojoules per gram (kJ/g), 1 kcal being equivalent to 4.184 kJ.1
In the Western countries (principally Australia, New Zealand, Canada, the EU, the U.S., and Switzerland), the standard for energy conversion for carbohydrates is the Atwater factor, i.e., 4 kcal/g or 17 kJ/g.2 The recently revised value is 3.75 kcal/g or 15.7 kJ/g.3 For the carbohydrates that resist absorption and digestion in the upper gastrointestinal tract but are completely or partly fermented in the intestine (i.e., the dietary fibers and the nondigestible oligosaccharides; see Chapter 6, Section 6.1.2), no universally accepted energy value exists. The proposed conversion factors are 0, 2.4, or even 4 kcal/g (0, 10, or 17 kJ/g), depending on the degree of their colonic fermentation.4 Modern research technology and methods have revealed newer dietary fibers and nondigestible oligosaccharides and also precise energy conversion factor values.5 Nevertheless, it must be kept in mind that various methods may yield results that differ due to natural variation and experimental error. It is the aim of the present chapter to review the data available and to propose a specific energy conversion factor for inulin-type fructans.
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