82 Introduction to Human Nutrition
(but not all) polysaccharides will be broken down to
release their component sugars. If these are fi ltered
away, the residue is “crude fi ber.” For many years this
was the way in which fi ber was measured for food
tables. However, acid hydrolysis breaks down many
carbohydrates that would not be digested in the small
intestine. So, in more modern methods, the food
residue is digested with amylase to hydrolyze the
starch to soluble sugars and oligosaccharides. The
latter are removed by fi ltration or by centrifugation
to leave a residue containing mainly dietary fi ber, pro-
teins, and inorganic materials.
The two main methods used to determine dietary
fi ber are chemical and gravimetric. In the chemical
method (used in the UK), the residue is subjected to
acid hydrolysis and the resultant sugars are measured
colorimetrically, by gas chromatography or by high-
performance liquid chromatography. The sum of all
these sugars constitutes the NSP. The chemical method
includes only carbohydrates in the NSP. In the gravi-
metric method (used in the USA and elsewhere), the
residue is dried and weighed, and the amounts of
protein and mineral materials present are subtracted
(after separate analyses). The gravimetric method
includes the NSP, plus other noncarbohydrate com-
ponents such as lignin and waxes. Recently, all coun-
tries in Europe have recognized the gravimetric
method as an approved method for measuring fi ber
in foods.
The main areas of disagreement now with respect
to fi ber are whether indigestible oligosaccharides and
sugars and nonplant compounds should be included
and whether the defi nition of fi ber should include
a physiological component. In Japan, fructooligo-
saccharides (FOSs) are classifi ed as dietary fi ber for
food-labeling purposes. However, FOSs and similar
compounds, being soluble in water, are not included
in the dietary fi ber methods, because they are fi ltered
out along with the sugars resulting from the starch
hydrolysis. Specifi c methods exist for FOSs and related
compounds, and they could be included as fi ber.
Certain animal-derived compounds, such as chitin
and chitosan, derived from the shells of shrimp and
crabs, are indigestible, would be included in the gravi-
metric fi ber analysis, and could be classifi ed as fi ber.
Chitin has some physiological properties, such as
cholesterol lowering, which are associated with dietary
fi ber. There are many other indigestible carbohydrate
and noncarbohydrate compounds, both natural and
artifi cial, that could be classifi ed as “fi ber” (e.g., poly-
dextrose, sucrose polyester, styrofoam). Should these
be included in dietary fi ber? In favor of this is the
argument that some of these materials have physio-
logical properties associated with fi ber, such as stool
bulking, or effects on satiety or blood glucose and
cholesterol. Against this is the feeling that dietary fi ber
should include only plant materials that are normally
present in the diet. These are not easy issues and they
have not been resolved.Intakes of dietary fi ber, oligosaccharides,
and other indigestible sugars
Vegetarians tend to have higher fi ber intakes than
omnivores. The typical intake of dietary fi ber in North
America and northern and central Europe is about
15 g/day. In Scandinavia and Italy, fi ber consumption
is 20–30 g/day, whereas in African countries such as
Uganda, Kenya, Malawi, and Nigeria intakes may be
as high as 50 g/day or more. Naturally occurring
oligosaccharides are consumed in legumes, onions,
fennel, chicory, and similar foods. Intakes in Western
countries are probably up to 2–4 g/day. Fructo- and
galactooligosaccharides are now being added to
certain “functional foods” in a number of countries,
and intakes from such sources may increase substan-
tially (up to 10–20 g/day). Many kinds of indigestible
or partially digested carbohydrates are entering the
food supply in dietetic, diabetic, or functional foods,
including sugar alcohols (polyols, e.g., sorbitol, man-
nitol, lactitol), polydextrose, resistant starch, hydroge-
nated starch, and other chemically modifi ed starches
and carbohydrates. Thus, the total amount of carbo-
hydrate entering the colon could become very sub-
stantial for people using these foods. Individually,
these ingredients are generally recognized as safe, and
evidence from populations consuming 50 g and more
NSP per day suggests that the colon has the capacity
to adapt to large increases in the load of carbohydrate.
However, safe upper limits of intake are unknown and
the health implications of an increased supply of a
wide range of carbohydrates to the colon are currently
based on inference rather than scientifi c data.Fermentation in the colon
The colon contains a complex ecosystem consisting of
over 400 known species of bacteria that exist in a sym-
biotic relationship with the host. The bacteria obtain
the substrates that they require for growth from the