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*
Center for Population Health and Nutrition, Monash University, Clayton, Victoria, Australia 3168 and
Department of Medicine, University of Melbourne, The Royal Melbourne Hospital, Melbourne, Victoria, Australia 3050
3To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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KEY WORDS: • dietary fiber • arabinoxylan • proliferation and fermentation • distal colon • rats
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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) and resistant starch
(Gibson et al. 1999
) compared to a fiber-free diet
induce a relative hyperproliferation in the distal colonic epithelium
of rats. GG (McIntyre et al. 1993
), pectin
(Jacobs and Lupton 1986
) and resistant starch
(Young et al. 1996
) have been reported to enhance tumor
development while wheat bran (WB) is protective against chemically
induced carcinogenesis (McIntyre et al. 1993
,
Young et al. 1996
). The anti-tumor effects of WB
also have been reported in human studies. The Australian Polyp
Prevention Project showed that the combination of fat reduction and a
supplement of WB reduced the incidence of large colorectal adenomas
(Macrae 1999
). Overall, of all the fibers tested in
experimental studies in both animals and humans, WB has been the most
effective fiber in protecting against colon cancer (Kritchevsky 1999
).
Arabinoxylan is a hemicellulose which has a xylose backbone and
arabinose side chains (Amodo and Neukom 1985
). It can be
found in many cereal grains. For example, it represents 60–69% of
nonstarch polysaccharide (NSP) in WB (Knudsen and Hansen 1991
, Ring and Selvendran 1980
,
Selvendran and Robertson 1990
) and 88% of NSP in wheat
endosperm (Selvendran and Robertson 1990
) although it
has slightly different chemical properties in different parts of the
wheat grain. In WB, arabinoxylan is acidic and mostly insoluble in
water while in wheat endosperm, it is neutral and more
water-soluble (Ring and Selvendran 1980
,
Selvendran and Robertson 1990
). Arabinoxylan from WB and
wheat endosperm also has been reported to be fermented differently.
Knudsen and Hansen (1991)
reported in a pig study that
the fecal recovery of arabinoxylan from wheat flour was ~10% while
it was 32 and 38%, respectively, for the fecal recovery of
arabinoxylan from wheat aleurone layer and WB. However, the effect of
arabinoxylan on luminal and mucosal characteristics of the colon is
largely unknown. As arabinoxylan is the major dietary fiber component
in cereal grains that make up a large proportion of our diet, it is
important to study its physiological effects.
Accordingly, the aim of this study was to examine the effect of
arabinoxylan in the rat colon and to compare the results obtained from
arabinoxylan to other well-characterized fibers, guar gum (highly
fermentable) and WB (slowly fermentable). An AX was extracted as a
by-product of wheat flour processing (wheat flour is predominantly
made from wheat endosperm). AX fiber is rich in NSP (70%) of which
90% comprises arabinoxylan (Lu et al. 2000
). We have
previously characterized the effects of several fiber types on colonic
luminal and epithelial indices (Folino et al. 1995
,
Gibson et al. 1999
) as well as on the activities of
brush border hydrolases (Gibson et al. 1999
). Therefore,
a similar protocol was followed in this study.
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Materials and Methods |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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Male Sprague-Dawley rats (n = 48, 180–210 g) were obtained from the Monash University Animal Services (Victoria, Australia). Animals were randomly divided into four groups and housed two to a cage (except on d 27 and 28) in drop-bottom wire cages to minimize coprophagy and to avoid the consumption of bedding as well as to allow fecal collection. On d 27 and 28, rats were housed individually for estimation of food intake and 24-h fecal output. The animal house was temperature-controlled (22 ± 1°C) and on a 12-h light-dark cycle. The Animal Ethics Committees of the Royal Melbourne Hospital and Deakin University (Melbourne, Australia) approved the study protocol.
Diets.
Rats were fed for 4 wk one of the diets containing either no fiber (NF)
or 100 g/kg of total dietary fiber from AX, GG or WB. The NF diet was
based on the AIN-93G purified rodent diet (Reeves et al. 1993
), modified by quantitatively replacing dextrinized
cornstarch and fiber with corn starch and by using soybean oil and
butter in the ratio of 50:50 as the total fat content. AX was extracted
from the by-product of wheat-flour processing. The composition
of AX has been reported elsewhere (Lu et al. 2000
). It
contains no fat, little protein and some starch but was rich in NSP
(699 g/kg) with a ratio of soluble to total NSP of 0.62. The NSP
(~90%) in AX was made up with arabinoxylan. WB was a gift from
Goodman Fielder Pty Ltd. (Lane Cove, NSW, Australia), and GG
was obtained commercially (Procol U; Polypro International Inc.,
Minneapolis, MN). WB was analyzed three times in duplicate for total
starch, protein, lipid, and total dietary fiber and water content by
the same methods as for the analysis of AX (Lu et al. 2000
). Briefly, total starch content was determined using the
Megazyme Total Starch Kit (Megazyme, Dublin, Ireland); nitrogen was
determined by semi-automated Kjeldahl apparatus (Gerhardt
Kjeldatherm; Turbosog and Vapodest, Bonn, Germany) before protein was
calculated using a conversion factor; lipid was measured
gravimetrically after chloroform/methanol (2:1) extraction; and total
dietary fiber content was determined using the procedure of the
Association of Official Analytical Chemists (AOAC; Prosky et al. 1985
); water content was assessed with a moisture analyzer
(Mettler LJ16; Mettler-Toledo AG, Greifensee, Switzerland). The AX
and WB diets were then prepared by adding an amount of total dietary
fiber from AX and WB, respectively, to achieve 100 g/kg of total
dietary fiber but adjusting for starch, protein and fat components of
the basal diet to allow for the contribution from the particular
supplement. The GG diet was prepared by adding 100 g of GG to
900 g of the control diet. Rats had free access to water and food.
The time period chosen for this study (4 wk) has been shown to be
adequate to stabilize fecal weight and pH (Goodlad and Mathers 1990
) and to induce significantly different changes in
epithelial turnover (Folino et al. 1995
, Gibson et al. 1999
) and on the activities of brush border hydrolases
(Gibson et al. 1999
) in healthy rats.
Measurement of body weight, daily food intake and fecal output, and collection of fresh fecal samples for short-chain fatty acids (SCFA) and pH.
Rats were monitored daily for general health and were weighed weekly.
Food intake (24-h) was monitored twice/wk in wk 2 to 4 by food
disappearance and corrected for the amount of spilled foods caught
under the cage. Rats were kept two per cage, and it was assumed that
rats in the same cage consumed equal amounts of food. Rats were housed
individually only on d 27 and 28 for more accurate estimation of food
intake and fecal output from each rat. The 24-h food intake data
obtained in wk 2 to 4 were not significantly different from that
obtained on d 27 and 28. Therefore, the average value for each rat
obtained from the last two consecutive days was used in the final
analysis. Daily fecal output was determined as described previously
(Folino et al. 1995
). Briefly, feces passed over a 24-h
period were collected from each rat after separation of food spills
from the feces using a perforated sheet of aluminum foil which was put
under each cage over the sawdust-filled collection tray. Daily
fecal output (dry weight) was obtained by freeze-drying the 24-h
fecal collection to a constant weight. The wet weight of daily fecal
output was calculated using the moisture content of the freshly passed
fecal pellets, which was also determined by freeze-drying. Fecal pH
was measured immediately in freshly passed fecal pellets, as described
previously (McIntyre et al. 1991
) using a
protein-resistant glass pH electrode with a 6-mm diameter tip
(Model AEP344; Activon Scientific Products, Carlton, Victoria,
Australia). A known amount (0.2–0.5 g) of fresh fecal pellet from each
rat was also collected in a 2-mL screw-capped vial and frozen
immediately at -70°C for subsequent analysis of SCFA.
Dissection and collection of cecal samples and tissues in the distal colon.
Rats were killed on d 29–32. Equal numbers of rats from each group
were killed on the same day, and rats were killed over a period of
2 h each day to minimize the effect of circadian variation. The
rats were injected with vincristine sulfate (David Bull Laboratory,
Melbourne, Australia) by intraperitoneal injection (1 mg/kg body)
3 h before killing to arrest cells in metaphase of the cell cycle
(Folino et al. 1995
) then killed by CO2
narcosis followed by cervical dislocation. The injection time was
staggered at 10-min intervals to enable killing and collection of
samples from each rat.
The peritoneal cavity was quickly cut open, and the cecum was cut adjacent to the ileo-cecal valve and ceco-colonic junction. The cecum including contents was weighed and placed immediately on top of a petri dish containing ice to minimize evaporation of SCFA. The pH of the cecal contents was obtained by inserting a protein-resistant pH electrode with a 6-mm diameter tip (Activon Scientific Products) through the proximal opening into the cecum while avoiding contact with the cecal wall. The cecum was then cut open along the small curvature, and a known amount of cecal content was collected and stored immediately at -70°C for subsequent analysis of SCFA. The remaining cecal contents were collected into tubes by gentle scraping and freeze-dried to constant weight to determine moisture content. The cecal wall was then washed with saline, dried by patting gently with clean tissues and weighed. The weight of the cecal contents was calculated by difference.
Two segments, each ~1 cm in length, were removed from the distal colon (about 2 cm proximal to the rectum). The most distal segment was immediately fixed in Bouin’s fixative (picric acid/formalin/galcial acetic acid, 75:2:15) for 4 h followed by washing and storage in 70% ethanol for histological examination. The proximal segment was slit open, mucosa laid uppermost on a microscope slide and scraped gently with another microscope slide. The mucosal scraping was immediately stored in a known amount of mannitol buffer (50 mmol/L D-mannitol and 2 mmol/L trizma base in distilled H2O, pH 7.4) at -70°C for subsequent analysis of brush border enzyme activities.
Measurement of epithelial proliferation in the distal colon.
Hematoxylin and eosin (H & E)-stained paraffin sections (2–3 µm)
were prepared from the fixed tissue. The prepared slides were coded so
that the observer was unaware of their identity. One observer read all
the slides under light microscopy. In other studies, 20 crypts have
been evaluated for the proliferation indices (Folino et al. 1995
). Our preliminary data, however, suggested that there was
no difference in the mean values obtained from examining 10 crypt
columns than 20 crypt columns (Rickard, K. L., 1993
).
Therefore, 10 well-oriented and longitudinally sectioned crypts
were examined for each rat in this study. The total number of
epithelial cell nuclei and the position and number of cells arrested in
metaphase were noted for each crypt and averaged for each animal. Crypt
column height (CCH), a measure of the total cell population, was
defined as the mean number of cells per crypt column. Cell turnover was
determined by the mitotic index (MI), which is calculated as the number
of cells arrested in metaphase divided by the total number of cells in
each crypt multiplied by 100.
Cell proliferation also was assessed in different zones as described
previously (Lipkin and Newmark 1985
). Briefly, the crypt
was subdivided into five longitudinal compartments from base
(compartment 1) to surface (compartment 5). Compartments 1 to 3 were
considered as the proliferative zone and compartments 4 and 5 as the
mature zone. The MI were also calculated for each zone as the number of
cells arrested in metaphase within each zone divided by the total
number of cells within the zone multiplied by 100.
Measurement of mucosal enzyme activities.
Alkaline phosphatase (ALP) and dipeptidyl-peptidase (DPPIV)
activities were measured because it has been suggested that ALP may be
influenced by epithelial irritation due to changes in luminal
conditions whileDPPIV may relate to differentiation status of the
epithelium (Gibson et al. 1999
).
Mucosal scrapings in mannitol buffer were mechanically homogenized
while keeping the tubes on ice, and Triton-X 100 was added to a
final concentration of 0.1%. ALP and DPPIV activities were assayed
spectrophotometrically using p-nitrophenyl phosphate and
glycyl-L-proline-p-nitroanilide
(Sigma-Aldrich, St. Louis, MO), respectively, as substrates
(Maroux et al. 1973
, Young et al. 1982
).
Enzyme activities were expressed relative to the mucosal protein
content, which was determined using bovine 
-globulin as a standard
(Bradford 1976
).
Measurement of cecal and fecal SCFA.
At the time of analysis, cecal and fecal samples were thawed at room
temperature for 1 h and mixed thoroughly with a known amount (1–2
mL) of distilled water. The samples were then centrifuged (GS-6R
centrifuge; Beckman Instruments Inc., Brea, CA) at 2,500 x g, 4°C for 30 min. An aliquot of 200 µL supernatant from
each cecal or fecal sample was pipetted into a 1.5-mL Eppendorf tube
and 20 µL of 3.5 mmol/L orthophosphoric acid was then added. An
aliquot of 20 µL of methyl-valeric acid (Sigma Chemical Co., St.
Louis, MO), as an internal standard, was also added into cecal or fecal
supernatants in the concentrations of 50 or 20 mmol/L, respectively.
Samples were then vortexed and centrifuged (Biofuge; Heraeus
Instrucments, Osterode, Germany) at 15,000 x g for 3
min. Finally, 1 µL of the clear supernatant was injected into a
capillary gas–liquid chromatography (Series 900 Autosystem; Perkin
Elmer, Norwalk, CT). Details of the column and standard SCFA mixture
have been reported previously (Phillips et al. 1995
). The gas chromatography conditions were as follows:
carrier gas pressure was 28 kPa, the temperatures for injector and
detector were 230 and 250°C, respectively. The oven temperature was
programmed at an initial temperature of 100°C for 8 min then
increased at the rate of 15°C/min to 130°C and held for 2 min.
Total SCFA was calculated as the sum of acetate, propionate and
butyrate.
Statistical analysis.
The effects of diets on fecal output, SCFA and pH in cecal and fecal contents, as well as variables relating to cell proliferation in the distal colon (CCH, the number of metaphase arrests per crypt and MI) were examined by ANOVA. Where significant dietary effects were detected (P < 0.05), multiple comparisons based on least significant difference were carried out. Variables that approximated a normal distribution are expressed as the mean ± SD in the text, Tables and Figures. Logarithmic transformations were adopted when variables were not normally distributed, and these results are shown as geometric mean with 95% confidence intervals.
The relationship between each of the luminal factors (fecal output, pH and SCFA concentration) and the MI of the epithelium in the distal colon was determined by partial correlation analysis, controlling for the effect of different diets.
All statistical analyses were performed using the statistical software package SPSS 8.0 for Windows (SPSS Inc., Chicago, IL). A P value of 0.05 or less was considered significant.
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Results |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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Daily energy consumption per rat was 385 ± 7, 275 ± 8, 278 ± 10 and 340 ± 9 kJ/d, respectively, for NF, AX, GG and WB groups. Compared with the NF group, mean daily energy consumption was 28.6, 27.8 and 11.6% less in the AX, GG and WB groups, respectively. Consequently, all the fiber-supplemented groups gained significantly less weight than the NF group. Final body weights in the AX, GG and WB groups were 20.9, 14.4 and 4.9% less, respectively, than the NF group. Final body weight was 368 ± 6, 291 ± 8, 315 ± 7 and 350 ± 7 g, respectively, for NF, AX, GG and WB groups.
Cecal mass and fermentation-dependent indices.
Rats fed the AX and GG diets had higher cecal wall weight and content
weight with higher moisture content than rats fed the NF and WB diets
(Table 1
). Cecal pH was significantly lower (P < 0.001) in all
the fiber-supplemented groups, the effects being most notable in
the AX and GG groups. The total SCFA concentration in the cecal
contents for the AX and GG groups was not different from that for the
NF group, while the concentration for the WB group was significantly
higher then that for the NF and GG groups. The total SCFA pool,
however, was significantly higher (P < 0.001) in all
the fiber-supplemented groups, these being the greatest for AX and
GG groups because of the larger volume of its contents. For the
individual SCFA, AX was associated with the highest acetate pool, while
GG produced more propionate and WB increased butyrate. Consequently,
the molar ratios of acetate, propionate and butyrate differed across
the dietary groups.
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Fecal output wet weight was the highest in AX group while both GG and
WB also produced significantly heavier stools than the NF group
(Table 2
). The water content of the feces differed significantly across the groups
(P < 0.001) in the following descending order: AX
> GG > WB > NF. Fecal pH did not differ among the
fiber-supplemented groups but all were significantly lower than
that in the NF group (P < 0.001). The fecal total SCFA
concentration was higher in both the GG and WB groups than that in the
NF and AX groups (P < 0.001). The daily excretion of
SCFA, however, did not differ among the fiber-supplemented groups
but all were significantly higher than that in the NF group
(P < 0.001). In contrast to the cecum, fecal acetate
concentration in the AX group was not different from that in the NF
group (although the daily excretion was significantly greater) and less
than that in both the GG and WB groups (P < 0.001).
The fecal concentration of propionate was significantly higher in all
fiber-supplemented groups than in the NF group (P
< 0.001) with the highest concentration seen in the GG group. The
fecal concentration of butyrate was the highest in the WB group, while,
in the AX group, it was similar to that in the NF group.
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CCH differed significantly across the dietary groups (P
< 0.001) in the following order: AX > GG > WB > NF (Fig. 1A
). The mean crypt columns were 79% longer in the AX group and 41% longer
in the GG group than those in the NF group. The number of mitotic cells
per crypt column followed a similar pattern. A marked increase in
proliferative rate (number of mitoses per crypt column) was observed in
the AX and GG groups as compared to the NF group, these being 4.5- and
2-fold, respectively (Fig. 1B)
. The turnover of epithelial cells, as
assessed by the MI, was also significantly different among all the
groups (P < 0.001). MI was 2.1-fold greater in the AX
group, 1.1-fold greater in the GG group, and showed a more modest 75%
increase in the WB group compared with the NF group (Fig. 1C)
.
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Effect of diets on mucosal hydrolase activities in the distal colon.
As shown in Figure 2
, mucosal hydrolase activities differed among the dietary groups. DPPIV
activities did not differ among the fiber-supplemented groups but
were significantly lower than that in the NF group. In contrast, ALP
were significantly higher in the AX and GG than in the NF or WB groups.
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The MI of the distal colonic epithelium was found to be related to
fecal output, fecal total SCFA concentration and in particular fecal
acetate and butyrate concentrations, and fecal pH by partial
correlation analysis, controlling for the effect of different diets.
Similar correlation coefficients and P values also have been
obtained for CCH, number of mitotic cells/crypt column and the fecal
output, SCFA concentration and pH (Table 3
).
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Discussion |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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). Thus, AX is rapidly fermentable and
behaves as a soluble fiber in the rat colon.
The reduction in weight gain observed in rats fed the AX and GG diets
when compared with that of the rats fed the NF and WB diets was most
likely a consequence of decreased energy intake. This response is
likely due to the high bulk (water-holding capacity) and high viscosity
of the soluble fibers which delay gastric emptying and result in
greater satiety. The impact of GG on satiety and weight gain in rats is
well-known (Johnson and Gee 1986
, Vachon et al. 1988
). GG, however, has not been successful in the
long-term treatment of obesity in humans mainly because most food
products incorporating GG are unpalatable. In contrast, we have found
that bread incorporated with 140 g/kg AX (which gives 100 g/kg of NSP
on dry weight basis) was as palatable as a bread containing 50%
wholemeal flour and 50% white flour in volunteers (Lu et al. 2000
). Thus, the observation that the AX-supplemented diet
led to weight loss in rats is worthy of further investigation,
specifically in relation to the management of obesity in humans.
The spectrum of SCFA produced differed across the three fiber types
examined in this study. There was a relative predominance of acetate
for AX, propionate for GG and butyrate for WB. Therefore, unlike WB, AX
used in this study is not a good fiber source for generating butyrate
in the distal colon. In a previous study in rats (Cheng et al. 1987
), fermentation of aleurone layers (an inner layer of WB
which is rich in arabinoxylan) also produced significantly less
butyrate than WB.
The high concentration of butyrate in the distal colon has been
suggested to be protective against colon cancer (McIntyre et al. 1993
). Butyrate has been shown to promote differentiation and
apoptosis (Hague et al. 1995
) and inhibit cell
proliferation in colon tumor cell lines (Gamet et al. 1992
), although the converse has been reported for the normal
human colon cells (Scheppach et al. 1992
). A recent
study, however, showed that oat bran-fed rats produced higher
concentrations of butyrate in the distal colon than do WB-fed rats,
but the incidence of tumor was significantly lower in the WB group
(Zoran et al. 1997
). This suggested that high butyrate
concentration in the distal colon may not be the only mechanism through
which WB protects against tumor formation in animal models. Some NF
components of WB such as phytochemicals (Lupton and Turner 1999
) also may be responsible for the protective effect. A
greater understanding of the mechanisms by which WB reduces colon
cancer risk clearly deserves further attention.
The effects on the proliferation of the epithelium in the distal colon
also differed across the fiber groups used in this study. As for
luminal effects, AX mimicked the effects of GG more closely than those
of WB, and it is also similar to those previously seen with resistant
starch (Young et al. 1996
). All fibers were trophic when
compared to the NF diet. The 1–2-fold increase in MI seen in the AX
and GG groups indicates that the life span of cells is reduced. This is
because the increase in the cell birth rate (number of mitoses per
crypt column) is out of proportion to the change in size of the total
cell population (the CCH). Whether this reflects a primary increase in
the rate of death of cells with a secondary proliferative response or
vice versa has not been ascertained. The MI of the mature zone in the
distal colon was increased only by the AX diet. This, however, does not
imply that AX is directly harmful to humans, since study diets were
constructed such that the fiber intake was entirely from a single,
purified source at moderately high concentrations. This contrasts with
the human diet, which usually contains a wide range of fibers from
different dietary sources. It has been shown that a combination of
rapidly and slowly fermentable fibers in the gut shifts the site of
fermentation distally in pigs (Govers et al. 1999
),
abolishes the increased epithelial proliferation in normal rats
(Key et al. 1996
) and minimizes carcinogenesis in
1,2-dimethythydrazine hydrochloride-treated rats (Young et al. 1996
) that are associated with rapidly fermentable
carbohydrate alone. Caution needs to be applied when extrapolating
effects from the experimental animals to humans.
Elevation in the rate of epithelial proliferation in the distal colon
has been suggested to be a consequence of the bulking effect of the
fibers (Hara et al. 1996
), the acidification of colonic
contents by diet modification (Lupton et al. 1985
) and
the increased delivery of SCFA to the epithelium (Sakata 1987
). The first two hypotheses are supported by the findings
of the present study, as the CCH, number of mitotic cells/crypt column
and MI of the distal colonic epithelium were positively related to
fecal output and inversely related to fecal pH. The last hypothesis,
however, is not supported by the present study as the CCH, number of
mitotic cells/crypt column and MI in the distal colonic epithelium were
found to be inversely related to the fecal concentrations of total
SCFA, acetate and butyrate.
Changes in epithelial proliferation in the distal colon also may be
associated with changes in the activities of mucosal brush border
hydrolases. Elevation in epithelial proliferation and turnover in the
distal colon correlate with low mucosal DPPIV activity (Gibson et al. 1999
). This suggests that decreased expression in the
mucosal DPPIV activity is associated with shorter life span of the
cells and therefore, decreased time available for differentiation to
occur (Gibson et al. 1999
). An inverse relationship
between the epithelial turnover and the mucosal DPPIV activity in the
distal colon was also obtained in the present study. Mucosal ALP
activities, on the other hand, showed a positive correlation with
epithelial proliferation (Gibson et al. 1999
),
suggesting that its expression in vivo represents more than just cell
maturation. ALP expression in the colonic epithelium may be induced as
a response to injury or stress, as it is in hepatocytes in the presence
of cholestasis (Hatoff and Hardison 1979
). In the
present study, the elevated epithelial turnover in rats ingesting AX-
or GG-supplemented diets was associated with considerable elevation
of ALP activities. This observation suggests that the soluble fibers
produced a "stressful" microenvironment for distal colonic
epithelium and that this may also be inducing an increased rate of cell
death.
In conclusion, the results of this study indicate that AX extracted from the by-product of wheat-flour processing behaves like a rapidly fermentable, soluble dietary fiber on both luminal and mucosal indices in the rat colon. Many of these characteristics of AX are similar to that of GG and resistant starch, but not WB.
The very low luminal acidity and the SCFA profile produced from colonic
fermentation of AX fiber may be less favorable in relation to colon
cancer risk. There is, however, evidence that AX may be important in
relation to events in the small intestine. We have recently completed a
study in which incorporation of 6 g AX into a meal improved
post-prandial glucose response in healthy humans (Lu et al. 2000
). This observation, in addition to the weight loss
observed during this study, suggests that AX may have a role in the
management of diabetes in humans. This area clearly requires further
investigation. In relation to colonic function, it is important that AX
is combined with a range of fibers in the diet, particularly insoluble
fiber such as WB, to neutralize any adverse effects of soluble fibers
to colon cancer risk.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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4 Abbreviations used: ALP, alkaline phosphatase activities; AX, arabinoxylan-rich fiber; CCH, crypt column height; DPPIV, dipeptidyl peptidase IV activities; GG, guar gum; MI, mitotic index; NF, no fiber; NSP, nonstarch polysaccharides; SCFA, short-chain fatty acid; WB, wheat bran.
Manuscript received November 9, 1999. Initial review completed December 21, 1999. Revision accepted March 24, 2000.
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