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,4
*
Department of Nutritional Sciences;
Research Animal Resources Center, the Graduate School;
**
Department of Animal Sciences; University of Wisconsin-Madison, Madison, WI 53706
2To whom correspondence should be addressed.
 |
ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • dietary fiber • in vitro fermentation • WB • OB • swine • rats
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). In addition, it has been shown
to be an antitumor agent using several cultured cell lines
(Bugaut and Bentejac 1993
) and a rat model
(McIntyre et al. 1993
). Molecular bases for this
antitumor property are being defined (Smith et al. 1998
,
Velazquez et al. 1997
). Wheat bran (WB) has been
proposed as protective in colon cancer because a higher proportion of
butyrate is generated by its fermentation, compared to the fermentation
of other fibers (Bugaut and Bentejac 1993
,
Klurfeld 1997
). Elevated concentrations of
n-butyrate have been reported during in vitro fermentation
of WB by some investigators (McBurney and Thompson 1990
,
McIntyre et al. 1993
, Salvador et al. 1993
), but not by others (Bourquin et al. 1992
).
A second possible protective mechanism for WB is that if it were
incompletely fermented, the unfermented WB-derived residue would
increase colonic lumenal contents and increase rate of transit of
material through the colon, thereby reducing the exposure of the mucosa
to carcinogens (Bugaut and Bentejac 1993
,
Klurfeld 1997
). The slow and incomplete fermentation of
WB, but not of oat bran (OB) (Chen et al. 1998
,
Nyman et al. 1986
, Stephen and Cummings 1980
), supports the role for WB of diluting carcinogenic agents
in the intestinal lumen. Lupton (1995)
proposed after a careful
comparison of results from in vitro and in vivo studies that WB is
protective against colon cancer because it is incompletely fermented
and not because fermentation of WB yields a higher proportion of
butyrate.
Propionate, another SCFA generated during fermentation of dietary
fiber, has been proposed as an inhibitor of hepatic synthesis of
cholesterol (Anderson et al. 1990
). Various clinical and
experimental studies have demonstrated that OB, but not WB, reduces
serum cholesterol levels (Anderson et al. 1990
,
Shinnick and Marlett 1993
). However, the many
experiments, using a variety of animal and in vitro models and
protocols, that have been conducted to evaluate the possible
hypocholesterolemic action of propionate have yielded conflicting and
inconsistent results (Bugaut and Bentejac 1993
).
One objective of this research was to compare and contrast the rate and
extent of fermentations of OB and WB and the accompanying SCFA
production to distinguish their hypothesized antineoplastic and
hypocholesterolemic functions. Fermentation in the large intestine of
monogastric species is a dynamic process that involves over 400 species
of microbes (Savage 1983
) and material much more complex
than the test fibers usually employed in in vitro fermentation studies
(Cummings 1981
). Further, a single measurement of
fermentation, typical of most in vivo studies, might not detect
elevations in specific SCFA in an ongoing process. Therefore, we also
used this experiment to evaluate the ability of an in vitro system
using physiological substrate and microflora to predict what is known
about fiber digestibility in humans. The physiological system used
ileal digesta as the substrate, and cecal microflora previously exposed
to the substrate as the source of inoculum, because prior exposure of
the inoculum to the substrate to be fermented, as well as the source of
inoculum, has been shown to influence fermentation (Monsma and Marlett 1995
, 1996
).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The ileal digesta that was to be fermented was collected from swine fed diets containing either WB or OB and in which cannulae had been surgically implanted in the terminal ileum. Cecal contents of rats that had been fed WB or OB were the inocula source used in an in vitro anaerobic incubation system. Nonlinear regression was used to characterize and quantitate the carbohydrate remaining and the SCFA present at time points during 96 h of fermentation to determine the rates and extent of change in the production of SCFA and the fermentation of carbohydrate. The experimental design was a 2 x 6 blocked factorial of two substrates (ileal digesta from swine fed WB or OB) and six fermentation durations (3, 6, 12, 24, 48 and 96 h), with replicate observations. The five pigs that provided the substrate served as the blocks. All animal protocols were approved by the College of Agricultural and Life Sciences Research Animal Resources Committee, University of Wisconsin-Madison.
Collection of digesta from swine.
Ileal digesta was collected from five barrows (1/2 Duroc 1/4 Large White 1/4 Landrace, The Swine Research Facility, University of Wisconsin-Madison), in which an ‘open type T’ polyethylene cannula (Ankom, Fairport, NY) had been implanted at the terminal ileum during aseptic surgery. Surgery was performed, and the animals were housed at the Livestock Laboratory, University of Wisconsin-Madison. The custom-designed cannula consisted of a flange in the gut lumen of polyethylene tubing (2.28 cm i.d., 3.25 cm o.d., 6.18 cm long) that had been cut in half lengthwise and rounded at the ends. The T side-arm (2.28 cm i.d., 2.6 cm o.d., 7.80 cm long) of the cannula was grooved so that polyethylene support discs, which prevented movement of the cannula, could be anchored.
Each pig was unfed for 48 h prior to surgery; mean weight of the five pigs at time of surgery was 43 ± 1 kg. The pigs were premedicated, intubated, put on anesthesia (1–2% halothane) and placed in right lateral recumbency. The ileum was exteriorized through a dorsal-ventral incision (10 cm) in the paralumbar area, and the cannula was inserted through a 4-cm incision in the antimesenteric border into the terminal ileum 15-cm anterior to the ileo-cecal junction. The ileal incision was closed with nonabsorbable suture material using a purse-string suture pattern. A peritoneal support disc (5.58 cm diameter with an opening in the center matching the dimension of the cannula), to which a circle of Dacron® material (Hancock Fabrics, Madison, WI) of the same dimensions had been sutured, then was placed around the T side-arm portion of the cannula; the fabric ring was anchored to the serosal surface of the intestine using nonabsorbable suture material. The cannula then was brought through a puncture incision in the abdominal wall. After the three layers of the body wall incision were separately sewn, an outer support disc (6.5 cm diameter) was snapped onto the cannula and secured flush to the abdominal wall with a C-clip. Antibiotic (Aureosulfamethazine, 2.5 g/kg body weight) was added to diet for 2 d postoperatively. Beginning 1 to 2 wk after surgery, pigs were housed individually in 244 cm X 56 cm crates to prevent the animal from turning around and to facilitate collection of ileal digesta.
Beginning 5 wk before surgery and continuing throughout the experiment,
swine were fed a semipurified diet at maintenance levels based on
metabolizable energy of: kcal/d = 109(body weight0.75)
(Agricultural Research Council 1981
) (Table 1
). Three meals of equal amounts were provided at 800, 1200 and 1700 h. The five pigs were food-deprived 24 h before a test meal
(420 g of dry food). The OB test meal was fed at 4 wk postoperatively
when the pigs weighed 47.6 ± 1.1 kg, and the WB test meal at 8 wk
postoperatively when pigs weighed 52.4 ± 0.8 kg. The test meals
were calculated to provide 50 g of dietary fiber/kg of diet from
OB or WB. Fiber sources were baked into muffins to simulate human food
preparation prior to incorporation into test meals. Purified diet
ingredients were adjusted to account for the protein, fat and starch
provided by the fiber sources. The macronutrient and fiber composition
of the test meals and maintenance diet for the swine were similar
(Table 2
). Test meals contained 0.5% of chromium sesquioxide (Fisher
Scientific, Pittsburgh, PA) in place of a comparable amount of
cornstarch to determine recovery of the test meals as ileal digesta.
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Collection of cecal inocula from rats.
The design of the experiment to collect cecal contents from rats
adapted to the test fibers has been described (Monsma and Marlett 1995
). Forty retired breeder rats were used (Harlan
Sprague Dawley, Indianapolis, IN) and were individually housed in
wire-bottom cages. One group (n = 20), mean
initial body weight of 453 ± 5 g, were fed purified diet
(AIN 1980
) in which cellulose was replaced with OB fiber
(Table 1)
. The second group (n = 20), initial mean
body weight of 447 ± 2 g, were fed purified diets containing
WB. Amounts of purified ingredients were adjusted to account for
macronutrients contributed by the brans (Monsma and Marlett 1995
). Mean daily food intakes and weight gains during the
12 d of feeding for the OB group (26 ± 3 g, 1.6 ± 0.2 g) and WB group (24 ± 1 g, 1.4 ± 0.1 g)
were not significantly different. Contents of four ceca, that were
harvested and pooled in an anaerobic chamber, were used to prepare the
inocula solution (Monsma and Marlett 1995
) for the ileal
digesta from a single pig.
In vitro fermentations.
Duplicate aliquots (1.52–1.55 g dry wt providing 2250 µmol of total
carbohydrate) of ileal digesta composite from each pig were fermented
in an anaerobic chamber for 3, 6, 12, 24, 48 and 96 h, using 67.5
mL of sterile buffer and 7.5 mL of inoculum solution for each flask
(Monsma and Marlett 1995
). At the designated time,
flasks were removed from the incubation chamber, and an aliquot (2 mL)
was taken for SCFA analysis. The remaining volume was frozen (-70°C)
within 0.5 h to stop fermentation (Shell Freezemobile, The Vitris
Company, Gardiner, NY) and lyophilized to dryness for subsequent
analysis.
Chemical analyses.
The swine maintenance diet and test meals were analyzed for dietary
fiber by an enzymatic-gravimetric procedure (AOAC Method 985.29 1990
), and crude protein (N X 6.25), crude fat and
starch, as previously described (Monsma et al. 1992
).
The chromium in the test meals was measured by the procedure described
by Guncaga et al. (1974)
. An enzymatic-colorimetric method was used
to determine the (1
3),(14)-ß-D-glucan content of
the OB test meal (Shinnick et al. 1988
).
Each 2-h collection of ileal digesta was analyzed for chromium, wet and
dry weight, and crude protein contents to determine that the digesta
collected during each 2-h period contained constituents which were
present in previous and subsequent collections. The composites of ileal
digesta were analyzed for crude protein, crude fat, starch, ash,
neutral and amino sugars by gas chromatography (Monsma et al. 1992
), and for the OB digesta,
(13),(14)-ß-D-glucan.
Terminated fermentations and inoculum solutions were analyzed for neutral and amino sugars, including ß-glucan for those containing OB, and Klason lignin. ß-glucan, non-ß-glucan glucose, arabinose, xylose and muramic acid accounted for 83% of the total carbohydrate present in the ileal digestas and therefore, are the only carbohydrates reported.
The non-ß-glucan-derived glucose was calculated as the difference
between total glucose and ß-glucan-derived glucose.
Non-ß-glucan-derived glucose, xylose and arabinose were used to
estimate the cellulose and arabinoxylan, respectively, the apparent
major polysaccharides in WB and OB dietary fiber (Marlett 1993
). The amino sugar muramic acid, a component of the
peptidoglycan murein found only in the cell wall skeleton of bacteria
(Schlegel 1988
), was measured to estimate changes in
microbial mass during fermentation.
Fermentation of the polysaccharides was assessed as the disappearance of the primary monosaccharides in each polysaccharide, which was calculated as the difference between the amount of the monosaccharide measured at the fermentation start and the amount remaining at the termination of a fermentation.
Acetate, propionate, i-butyrate,
n-butyrate, i-valerate and
n-valerate were measured in duplicate by gas
chromatography as previously described (Monsma and Marlett 1995
). Only acetate, propionate and n-butyrate
were reported as they accounted for 
93% of the total SCFA
produced.
Statistical analyses.
The statistical model used was the General Linear Model procedure.
Regression curve fittings were performed using TableCurve 2D (1994).
Data were tested for homoscedasticity by Bartlett’s test (Zar 1974
) and square root transformed if necessary. ANOVA was
performed using GB-STAT (1994)
. When significant (P
< 0.05) differences were observed, means were compared by the
Fischer’s protected least significant difference method. Data are
reported as means ± SEM.
Composition of swine ileal digesta, performance of the rats that provided the cecal inocula, and the SCFA and sugar contents of the fermentations terminated at each time point were compared by one-way ANOVA.
A nonlinear regression procedure was used to fit the disappearance of
ß-glucan and non-ß-glucan glucose, arabinose and xylose to the
first-order exponential curve, y = a(1 +
e-bx). The initial rates of disappearance (µmol/h) of the
individual carbohydrates were calculated by multiplying the maximum
carbohydrate disappearance by the fractional rate constant
(Monsma and Marlett 1996
). Two-way ANOVA was used to
compare the main effects of carbohydrate and ileal digesta and their
interaction on the initial rate and maximum disappearance of the
individual carbohydrates.
Acetate, propionate and n-butyrate production data also
were fitted to the first-order exponential curve, y
= a(1 + e-bx), to calculate initial rates (µmol/h)
and maximum production (µmole) of individual SCFA (Monsma and Marlett 1995
). Two-way ANOVA was used to compare the main
effects of SCFA and ileal digesta and their interaction on the initial
rate and maximum disappearance of individual SCFA.
Linear regression was used to determine efficiency of the microflora
fermenting ileal digesta from either OB or WB, as previously described
(Monsma and Marlett 1996
). Fermentation efficiency is
defined as the change in percentage of muramic acid/100 µmole
carbohydrate disappeared. One-way ANOVA procedures were used to
analyze the effect ileal digesta had on the fermentation efficiency of
the microflora.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Similar amounts of chromium from the two test meals were recovered in
ileal digesta, 69.2 ± 5.4% from pigs fed the OB meals and 64.2
± 5.4% from pigs fed the WB meals. The mean dry weight output,
crude protein (N X 6.25) content and percent moisture of the digestas
collected from swine fed OB, 46.4 g, 9.2 g and 93.2%,
respectively, were not significantly different from ileal digesta from
swine fed WB, 47.2 g, 8.6 g, 93.6%, respectively. No
significant differences were observed in the compositions of the ileal
digesta composites prepared from the 2-h collections from swine fed the
two diets (Table 3
).
|
). The moisture content of the collections remained constant at 93 to
95% (data not shown). The percentage of total dry weight of ileal
digesta collected and the percentage of total wet weight, chromium and
crude protein collected every 2 h during each test meal were
significantly correlated, r = 0.87 (P
< 0.05). The percentage of the total chromium and crude protein
collected at each 2 h following feeding of the OB and WB diets
were also significantly correlated, r = 0.72
(P < 0.05).
|
Glucose, xylose and arabinose accounted for 83% of the carbohydrate at
0 h fermentation of ileal digesta from swine fed either bran
(Table 4
). Fucose, galactose, glucosamine and galactosamine, the sugars in mucin
(Monsma et al. 1992
), represented 12–13% of the total
carbohydrate.
|
After the initial 3 h, significantly more of the total
carbohydrate in the OB ileal digesta disappeared than in the WB ileal
digesta at every time point measured (Fig. 2
). Carbohydrate disappearance did not increase significantly after the
12-h time point during WB fermentation or after 24 h during
fermentation of OB ileal digesta.
|
). Initial fermentation rates of arabinose and xylose were similar in
the two digestas. The maximum disappearance of arabinose, but not of
xylose, was significantly less from the WB sample than from the OB
digesta.
|
).
|
Significantly more total SCFA were produced at every time point during
fermentation of the OB digesta compared to WB digesta, although SCFA
production did not increase significantly after 48 h (Fig. 2)
.
Acetate production dominated all fermentations (Table 6
). The initial rate of propionate production from OB ileal digesta was
three times faster than that from WB digesta, whereas the initial
production rates of n-butyrate from both digestas were
similar. Maximum productions of propionate and n-butyrate
were greater from the fermentation of OB, compared to WB digesta. A
significantly greater proportion of propionate and significantly
smaller proportion of acetate were produced during the first 24 to
48 h of fermentation of OB than was produced by fermentation of WB
(Fig. 4
). The source of fiber in the digesta had no effect on the proportions
of total SCFA produced as n-butyrate. The molar proportion
of individual SCFA did not change after 48 h of fermentation.
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The mass of the bacteria, estimated by the measurement of muramic acid
in the fermentation, was significantly greater at 6, 48 and 96 h
during the fermentation of OB digesta, compared to WB digesta
(Fig. 5
). Bacterial mass increased to a maximum of 133% of the initial amount
at 48 h in the OB fermentations, but to only 117% at 24 h in
the WB fermentations. At 96 h, the muramic acid level in the OB
fermentations remained at 125% of initial amount, compared to 86% of
the initial level in the WB fermentations. However, bacterial
efficiencies of carbohydrate utilization by bacteria fermenting digesta
containing either bran were not significantly different; the change in
the percentage of muramic acid was 3.6 ± 1.2%/100 µmol
carbohydrate disappeared in the OB fermentations and 5.2 ± 1.1%/100 µmol carbohydrate disappeared in the WB fermentation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). For example, we found that
ileal digesta from both rats (Monsma et al. 1992
) and
swine (Monsma and Marlett, unpublished data) fed purified
fiber-free diets contained ~500 µmol carbohydrate/g of dry
weight ileal digesta. Further, as much as 20% of the total SCFA
generated during microbial fermentation of the glycoprotein mucin,
produced endogenously by the gastrointestinal tract, were propionate
and n-butyrate (Monsma and Marlett, unpublished data). Ileal
digesta was collected from pigs because the digested remnants of
defined meals could be collected in sufficient quantity to analyze and
ferment from this animal model.
The similarity among the proximate compositions of the swine ileal
digesta used in this study, other swine ileal digesta we have analyzed
and ileal effluent from humans supports our decision to use swine ileal
digesta as the substrate to model human ileal digesta. McBurney et al. (1988)
fed a human ileostomate a basal diet containing 13 g/d of fiber
and the same diet supplemented with white bread, OB, kidney beans or
red lentils. In these studies, the mean (±SEM) content of
the ileal effluent was (g/kg dry digesta) 217 ± 18 protein, 27
± 6 fat, 143 ± 17 ash and 611 ± 37 carbohydrate by
difference. Lia et al. (1996)
fed nine ileostomy subjects a basal diet
supplemented with bread containing only white flour or supplemented
with OB, OB and ß-glucanase or a barley fraction. In these studies,
the mean content of the ileal effluent was (g/kg dry digesta) 236
± 9 protein, 39 ± 12 fat and 725 ± 18 carbohydrate by
difference and ash combined. The mean content of ileal digesta
collected from pigs fed a fiber-free test meal or one containing
5% dietary fiber from canned peas was (g/kg dry digesta) 215 protein,
45 fat, 264 ash and 476 carbohydrate by difference (Marlett and
Longacre, unpublished), similar to the composition of the swine ileal
digesta containing WB or OB used in this study.
The rat was the inoculum source as it was more cost- effective and
justifiable than using swine for this purpose. The cecum was the
inoculum source because that is the microbial population that is first
exposed to ileal residue in vivo. Our experience indicates that rat
fecal inoculum does not ferment to the same extent as cecal inocula
from the same animal prefed the test material to be fermented
(Monsma and Marlett 1995
, and 1996
).
Savage (1983)
views feces as a waste product and proposed that
determining the effect of diet on biochemical activities in the
proximal colon lumen from biochemical activities in feces may be
misleading. Actual measurements made by MacFarlane et al. (1992)
using
human colonic contents support Savage’s contention. MacFarlane et al. (1992)
reported that bacteria from the ascending colon of two sudden
death victims generated five to eight times more SCFA than did bacteria
from the sigmoid-rectum region of the same subjects. However, rat
cecal inocula production of SCFA from pectin and purified soybean fiber
was not different than what was produced when human fecal inocula was
used to ferment the same substrates (Barry et al., 1995
). In vitro fermentation using human fecal inocula of 11 of
12 dietary fiber concentrates or fiber extracted from mixed diets were
generally similar to the net digestibilities of the sugars from the
same fibers in the same humans from which the fecal inocula were
collected (Daniel et al. 1997
, Wisker et al. 1998
). The one fiber source that was fermented much more
extensively in vitro vs. in vivo was a barley concentrate that
contained a high proportion of total fiber as cellulose.
Our in vitro fermentation results are similar to net fiber
digestibility in vivo in humans and rats. The apparent digestibilities
of WB fiber in rats (Hansen et al. 1992
, Nyman et al. 1986
), of 41 and 49%, are similar to digestibilities
reported in humans, of 34% (Nyman et al. 1986
)
and 56% (Chen et al. 1998
), and to the disappearance of
WB-derived sugars, of 47%, in our in vitro fermentation system.
Likewise, the disappearance of OB-derived sugars in our in vitro
system, of 84%, is similar to apparent digestibility of OB in the rat
(Hansen et al. 1992
), of 93% and humans (Chen et al. 1998
), of 96%. These in vitro and in vivo results of WB
and OB fibers across species are remarkably similar, in light of the
facts that they were conducted by different laboratories using
different substrates. In humans, OB dietary fiber increases fecal
bacterial mass (Chen et al. 1998
). Changes in the
muramic acid content of the in vitro system we used also are consistent
with these in vivo observations.
The initial increase in propionate in our study corresponded with the
rapid disappearance of ß-glucan in the OB digesta fermentation,
suggesting that fermentation of ß-glucan is at least one source of
the increase in propionate. This observation supports those by
Bach Knudsen et al. (1993)
who reported in vivo increases in propionate in
the ceca of swine fed diets containing either OB or ß-glucan-enriched
fractions, compared to diets containing the insoluble residue of OB.
The larger molar proportion of propionate we measured during in vitro
OB fermentation is consistent with the data of Jackson and Topping (1993)
. They observed a larger proportion of propionate was generated
in the ceca of rats consuming OB, compared to cecal SCFA composition of
the group fed WB. Thus, some in vitro and in vivo data are consistent
with the proposal that a component of the hypocholesterolemic effect of
some dietary fibers could be caused by propionate inhibition of hepatic
cholesterol synthesis (Anderson et al. 1990
). However,
other studies (McBurney and Thompson 1990
,
McIntyre et al. 1993
) did not observe elevated molar
proportions of propionate when OB was fermented, relative to when WB
was fermented in vitro. As comprehensively reviewed by Bugaut and Bentejac (1993)
, data to support this hypothesis are not compelling.
Rather, the hypocholesterolemic action of some fibers appears to be
related to their effects on sterol balance (Marlett 1997
). Viscous soluble fibers decrease bile acid absorption in
the terminal small bowel (Marlett et al. 1994
) which
stimulates hepatic bile acid synthesis that uses LDL-cholesterol as
its primary substrate (Schwartz et al. 1982
).
Our observation that fermentation of WB ileal digesta did not produce a
greater proportion of SCFA as n-butyrate than OB digesta, but
rather a smaller absolute amount of n-butyrate, agrees with those
of Bourquin et al. (1992)
, who fermented dietary fiber either isolated
from WB or OB, or the fiber-derived polysaccharides extracted and
subsequently recombined. Neither our findings or those of Bourquin et al. (1992)
support the hypothesis of McIntyre et al. (1993)
that
n-butyrate from WB fermentation is a significant
protective mechanism against tumor formation. Others (McBurney and Thompson 1990
, Salvador et al. 1993
) who
observed increased n-butyrate production during in vitro
fermentation of WB used WB that contained residual starch. In vitro
fermentation of starch (Englyst and Macfarlane 1986
)
produces a significant proportion of SCFA as n-butyrate,
and it is possible that fermentation of the starch contaminating the
WB, and not the WB fiber, was responsible for the production of more
butyrate in these studies.
The greater microbial efficiency of carbohydrate utilization we
observed during fermentation of WB ileal digesta, compared to OB ileal
digesta, in conjunction with the less complete fermentation of WB
carbohydrate, suggests that the microflora used additional sources of
carbon for growth. Protein fermentation has been estimated to account
for 17% of the SCFA in the cecum to 38% in the sigmoid/rectum of
humans (Macfarlane et al. 1986
), and it likely occurred
during our studies. At every time point in our study at least 1.5 to 2
times more SCFA were being produced than what was predicted by the
stoichiometric equation for carbohydrate fermentation developed by
Miller and Wolin (1979)
.
In summary, although we observed a larger proportion of propionate
produced during OB fermentation, the majority of the evidence suggests
that the hypocholesterolemic mechanism for viscous, soluble dietary
fibers is not propionate inhibition of cholesterol synthesis
(Bugaut and Bentejac 1993
, Marlett 1997
).
The lack of increase in butyrate production during WB fermentation in
our studies supports the contention that poorly-fermented WB is
protective against colon cancer because it dilutes lumenal contents,
not because it provides butyrate for the colonic mucosa (Bugaut and Bentejac 1993
, Klurfeld 1997
, Lupton 1995
).
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ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
3 Current address: Department of Radiation Oncology, Henry Ford Hospital, 2799 W. Grand Blvd., Detroit, MI 48202-2608.
4 Current address: Laboratory Animal Resource Center, University of California, San Francisco, San Francisco, CA 94143-0564.
5 Abbreviations used: oat bran, OB; SCFA, short-chain fatty acids; wheat bran, WB.
Manuscript received August 9, 1999. Initial review completed September 17, 1999. Revision accepted November 29, 1999.
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REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
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Cummings J. H. Short chain fatty acids in the human colon. Gut 1981;22:763-779
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