Beer : Health and Nutrition

94 Chapter Four
Fibre
The term is unfortunate, for not all of the components generally considered under this
heading are actually brous. Perhaps ‘roughage’ after all is no worse a term (Kritchevsky
& Bon eld 1995).
The majority of materials considered to be dietary bre are plant cell wall components
including celluloses, hemicelluloses (such as are found in the cell walls of barley) and
pectins. There can be a further division into soluble and insoluble fractions, though it
must be remembered that this refers to what is solubilised in standard laboratory analytical
procedures and not necessarily what happens in the gastrointestinal tract.
Insoluble components may serve to delay the digestion of other components via
physical blocking. The soluble components, on the other hand, will afford increased
viscosity if they are of high molecular weight, thereby lengthening transit time in the
gut and also the rate at which digestion products (e.g. glucose) are taken through the
gut wall. This may also explain the impact of dietary bre in reducing the absorption
of cholesterol.
These materials hold water, lead to a softening of stools and accelerate the passage
of the stool through the large intestine. Research in recent years has demonstrated the
merits of bre in lowering plasma cholesterol levels, reducing cancer incidence, lessening
the need for diabetics to take insulin, and so on. The understanding of the precise
structural features in bre which lead to best effect is less than clear (see Johnson 2003).
The beer carbohydrates comprising soluble bre (which will include the degradation
products of barley cell wall polysaccharides and also the dextrins produced during starch
degradation; see Chapter 3) escape absorption in the small intestine, thus becoming
nutrients for bacteria located in the large bowel. The importance of these organisms
to gut function and health has become well recognised in recent years and has led to
the concept of probiotics and prebiotics. Probiotics are organisms, notably lactobacilli
and bi dobacteria, which are added to diet to boost the ora in the large intestine. For
example they are added to yoghurt (Young 1998). Prebiotics are nutrients that boost
the growth of these organisms. These may include oligosaccharides that may promote
the growth of the appropriate organisms (Gibson 1999; Roberfroid 2001). Microbes
in the large intestine produce methane and other gases as a result of their metabolism,
and the atulence experienced after drinking beer may relate to this activity (but see
Chapter 6).
It also needs to be borne in mind that materials capable of binding to the bre passing
straight through the digestive system will also be less available to the body. This might
include certain minerals and vitamins (Prosky 2003).