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Lot of debate is going on about the definition and measurement of dietary fibre. The term dietary fibre was first adopted in the 1950s to describe the plant cell wall components of foods. The physiological significance of dietary fibre came to the fore in the 1970s by Burkitt who recognised that fibre improves bowel function. This increasing awareness of potential health benefits of ‘dietary fibre’ did give raise to the development of fibre analysis methods. Unfortunately, numerous definitions of dietary fibre and methods to determine dietary fibre have led to inconsistent and confusing data in FCDBs.

According to the EFSA statement on fibre, dietary fibre is defined as as non-digestible carbohydrates plus lignin.

The main types of total dietary fibre are:

• Non-starch polysaccharides: cellulose, hemicelluloses, pectins, hydrocolloids (e.g. gums, mucilages)

• Resistant oligosaccharides: e.g. fructo-oligosaccharides (FOS), galacto-oligosaccharides

• Resistant starch:

• Lignin

With respect to the methods for dietary fibre analysis, the current situation can be summarised by two opposing views:

1) Dietary fibre is defined as undigestible carbohydrates (and lignin). Methods to measure fibre defined in this way are based on simulating food digestion in the small intestine (AOAC method, also called Prosky method).

2) Dietary fibre is defined as non-starch polysaccharides (NSP), the major component of the plant cell wall material. The methods based on this definition measure plant cell wall polysaccharides (Englyst or NSP method).

For food composition databases the debate has ended in favour of the AOAC approach for almost all countries.

Next to those two approaches you will sometimes find the term ‘crude fibre’. The term crude fibre originates from fibre analysis methods used in the analysis of animal feed. Crude fibre is defined as the residue that remains after extraction and hydrolysis of polysaccharides by means of hot acid and hot alkali. This residue contains only part of the lignin, cellulose and hemicellulose fractions. However, for human nutrition it is not very useful to define fibre as ‘crude fibre’ since crude fibre bears little relation to the plant cell wall polysaccharides that are believed to be associated with physiological changes in man.

Go to the next page to learn more about the AOAC and Englyst method.