Introduction
Important metabolic effects of dietary fibre in
terms of reduction of cardiovascular disease,
diabetes and cancer were originally suggested by
Burkitt and Trowel in their dietary fibre hypothesis.1
Since then many studies have been undertaken and
a significant body of work supports a positive role
for fibre in the prevention of chronic disease.
However, mechanisms explaining this remain uncertain. The degree of protection from chronic
diseases offered by fibre is uncertain and even the
definition of fibre itself is a subject for debate.
The most recent definition of fibre to emerge is
that resulting from the dietary reference intake
(DRI) deliberations.2 Here three classes of fibre are
defined. Dietary fibre: ‘‘the nondigestible carbohydrate and lignin that are intrinsic and intact in
plants’’. This fraction also includes wheat bran and
oat bran even though they are technically no longer
‘‘intact’’ in plants. Functional fibre: ‘‘isolated, nondigestible carbohydrates that have beneficial effects in humans.’’ These beneficial effects are not
defined, leaving the field open to different possibilities, but the benefits must be demonstrated.
Fructo-oligosaccharides and resistant starch are
included in this definition. Finally, total fibre is the
sum of dietary fibre and functional fibre. The
adequate intake was defined as 38 g/d for men
and 25 g/d for women, levels which are not out of
line with current guidelines.2
The terms soluble and insoluble fibre were not
retained in the DRI document. Nor was the term
viscous fibre defined despite good reasons including
the use of the term by the Adult Treatment Panel III
(ATP III) of the National Cholesterol Education
Program (NCEP) in connection with cholesterol
reduction.3 Despite a generally favourable assessment of the role of fibre by the DRI Committee, the
American Diabetes Association remains skeptical
about the metabolic value of fibre.4 These negative
sentiments have been countered by the NCEP ATP III
with advice to increase the intake specifically of
viscous fibre to 10–25 g/d in order to achieve a
more effective lowering of cholesterol.3 A major
focus of the present discussion will therefore
centre on the metabolic effects of viscous fibres.
The lack of metabolic effect of non-viscous
particulate fibres on systemic lipid and carbohydrate metabolism despite their apparently protective effect in reducing the risk of developing
diabetes and cardiovascular disease will also be
discussed. This emphasis in no way diminishes the
role of particulate fibre in colonic health, fecal
bulking associated with pentose content,5 and
possibly colon cancer risk reduction.6–9
IntroductionImportant metabolic effects of dietary fibre interms of reduction of cardiovascular disease,diabetes and cancer were originally suggested byBurkitt and Trowel in their dietary fibre hypothesis.1Since then many studies have been undertaken anda significant body of work supports a positive rolefor fibre in the prevention of chronic disease.However, mechanisms explaining this remain uncertain. The degree of protection from chronicdiseases offered by fibre is uncertain and even thedefinition of fibre itself is a subject for debate.The most recent definition of fibre to emerge isthat resulting from the dietary reference intake(DRI) deliberations.2 Here three classes of fibre aredefined. Dietary fibre: ‘‘the nondigestible carbohydrate and lignin that are intrinsic and intact inplants’’. This fraction also includes wheat bran andoat bran even though they are technically no longer‘‘intact’’ in plants. Functional fibre: ‘‘isolated, nondigestible carbohydrates that have beneficial effects in humans.’’ These beneficial effects are notdefined, leaving the field open to different possibilities, but the benefits must be demonstrated.Fructo-oligosaccharides and resistant starch areincluded in this definition. Finally, total fibre is thesum of dietary fibre and functional fibre. Theadequate intake was defined as 38 g/d for menand 25 g/d for women, levels which are not out ofline with current guidelines.2The terms soluble and insoluble fibre were notretained in the DRI document. Nor was the termviscous fibre defined despite good reasons includingthe use of the term by the Adult Treatment Panel III(ATP III) of the National Cholesterol EducationProgram (NCEP) in connection with cholesterolreduction.3 Despite a generally favourable assessment of the role of fibre by the DRI Committee, theAmerican Diabetes Association remains skepticalabout the metabolic value of fibre.4 These negativesentiments have been countered by the NCEP ATP IIIwith advice to increase the intake specifically ofviscous fibre to 10–25 g/d in order to achieve amore effective lowering of cholesterol.3 A majorfocus of the present discussion will thereforecentre on the metabolic effects of viscous fibres.The lack of metabolic effect of non-viscousparticulate fibres on systemic lipid and carbohydrate metabolism despite their apparently protective effect in reducing the risk of developingdiabetes and cardiovascular disease will also bediscussed. This emphasis in no way diminishes therole of particulate fibre in colonic health, fecalbulking associated with pentose content,5 andpossibly colon cancer risk reduction.6–9
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