
involved, which are largely dependent on the type
and form of the guar gum ingested. Much of the
literature indicates that guar gum decreases the rate
of glucose absorption into the hepatic portal vein
by inhibiting the processes associated with digestion
and absorption of available carbohydrates. These
processes include gastric function, intestinal transit
and mixing, a-amylase–starch interactions, and the
movement of products of starch hydrolysis to the
gut mucosa.
0014 A number of experiments in humans and animals
have shown that guar gum reduces the rate of gastric
emptying of a meal. However, there are also studies
that have shown no effect or even sometimes an ac-
celeration in gastric emptying after the ingestion of
guar gum. These contradictory results probably arise
from differences in the type of guar gum used, the
way in which it was administered, the proportion of
solids and liquids in the meals, and the techniques
used to measure gastric emptying. In general, it is
considered that guar gum may reduce the rate of
gastric emptying under some conditions, but this
action is unlikely to be the only mechanism. Other
groups have shown guar gum has additional effects
on gastric function. In studies in dogs, guar gum was
reported to impair gastric trituration and sieving by
increasing the viscosity of the stomach contents. It
was shown that there was a significant increase in
the proportion of larger particles of food entering
the small intestine when guar gum was incorporated
into the diets. Possible explanations for these findings
include suggestions that the increased viscosity stabil-
izes the suspension of larger food particles, which are
likely therefore to escape maceration in the antrum of
the stomach, and/or that the guar gum alters the
contractile pattern of the terminal antrum, thus
impairing the ability of the stomach to retain large
particles.
0015 There is evidence from human and animal studies
that guar gum delays the transit of digesta in the small
intestine. The postprandial pattern of gut motility
also seems to be influenced by guar gum and other
types of dietary fiber. Thus, whereas wheat bran and
cellulose-supplemented diets were reported to pro-
duce prolonged bursts of intestinal contractions, guar
consumption caused continuous contractions with a
50% reduction in amplitude compared with the other
types of fiber. The effect of guar gum on the mixing
behavior of digesta at different sites of the gastro-
intestinal tract has yet to be investigated, but it is
likely to be extremely complex. It has been suggested
that an increase in the viscosity of digesta will pro-
duce laminar or ‘streamline’ flow, rather than turbu-
lent or disorderly flow, which is characteristic of less
viscous fluids and facilitates efficient mixing of
digesta in the gut. An inhibition of the digesta flow
rate will inhibit physical mixing of nutrients and
enzymes (e.g., pancreatic amylase). Also, laminar
flow behavior would almost certainly have an effect
on the rate at which nutrients are exposed to the
epithelial surface and then absorbed into the hepatic
portal vein.
0016However, an explanation of the precise mechanism
by which guar gum modifies gut function is still elu-
sive, despite the plethora of clinical and physiological
studies that have been undertaken. The problem is
that researchers understand little about the behavior
of guar gum in the human gastrointestinal tract.
Digesta is an extremely complex heterogeneous ma-
terial and the effects of guar gum on this system have
not been studied in great detail. Much of the work
that has been done has involved investigating digesta
in the stomach and small intestine, since it is assumed
that guar gum has negligible effects on viscosity in the
large intestine due to depolymerization by bacterial
fermentation. There are a number of problems asso-
ciated with measuring digesta rheology in vivo.In
human subjects, there are obvious practical difficul-
ties in gaining access to the sites of interest in the gut.
Notwithstanding the initial problems involved with
sampling intestinal contents, particularly in humans,
the rheological properties of digesta will depend on
the precise location of the sampling site. Thus, digesta
is subjected to dilution by gastric secretions and then
concentration by absorption of water, by both the
intestine and the guar gum, at it passes further along
the intestinal tract. Also the samples collected need to
be tested quickly to prevent drying or dissolution of
particulate materials. In the case of animal experi-
ments, this requires access to rheometers or other
measuring devices in the animal house.
0017Many factors complicate the interpretation of the
rheological behavior of digesta containing guar gum.
These include a lack of information on the hydration
kinetics of guar gum in vivo and the contribution of
undissolved food particulates to viscosity. Therefore,
to enhance our understanding of the physical proper-
ties of digesta it is important to study model systems
of entangled networks filled with particulates, al-
though in vivo other factors such as gastrointestinal
motility and fluid secretion/absorption also play a
crucial role. In recent years, the rheological properties
of guar gum solutions with increasing particulate
concentrations have been investigated. The particu-
lates studies included materials that were essentially
spherical and rod-like in shape (i.e., starch granules
and microcrystalline cellulose, respectively). The
effect of particulates or ‘fillers’ is primarily to increase
the viscosity above that of the pure guar gum system,
as shown in Figure 6. The initial Newtonian flow
GUMS/Nutritional Role of Guar Gum 3017