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CSIRO Health Sciences and Nutrition, Adelaide 5000, Australia
7To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • calcium • pigs • rice • short-chain fatty acids • starch
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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). The commercial
production of brown rice (BR) which has been heat-stabilized
through processes such as parboiling or extrusion (Sayre et al. 1982
) means that this product now is available to populations
where WR was the only product consumed normally. In addition to
retention of those nutrients which are lost during polishing,
heat-stabilized BR may have additional advantages. Studies in pigs
have suggested that BR may be a source of resistant starch (RS) which
may be protective against bowel disease (Topping and Bird 1999
).
NSP resist human small intestinal enzymatic digestion and enter the
large bowel, essentially unmodified. In that viscus they increase fecal
bulk which is thought to be a part of the agency whereby fiber protects
against constipation and diverticular disease (Topping and Wong 1994
). Additionally, NSP are fermented by the colonic
microflora leading to the greater availability of short-chain fatty
acids (SCFA), principally acetate, propionate and butyrate
(Cummings and Macfarlane 1991
). These acids exert a
number of general actions on the large bowel which include lowering of
colonic pH and increased electrolyte and fluid absorption which assists
in the prevention of diarrhea. Individual acids appear to promote
colonic muscular activity in a dose-dependent manner
(Cherbut 1994
) and large bowel blood flow through
relaxation of the vasculature (Mortensen et al. 1991
).
Butyrate may be most important for the maintenance of colonic health.
This acid is a major metabolic fuel for normal colonocytes
(Roediger 1982
), its infusion may relieve ulcerative
colitis (Scheppach et al. 1992
) and its presence can
assist in the maintenance of a normal cell phenotype through a number
of mechanisms (Kruh et al. 1995
). Propionate also may be
of metabolic importance in the colon because it exerts some of the
antineoplastic effects of butyrate although at much higher levels
(Mortensen and Clausen 1995
). Elevated concentrations of
propionate in the large bowel also may suppress cholesterol synthesis
in that viscus (Hara et al. 1999
).
It appears that, quantitatively, the most important substrate for the
colonic microflora is starch (Cummings and Macfarlane 1991
). Of special interest is the fact that human large bowel
fermentation of RS appears to favor butyrate production (Noakes et al. 1996
, van Munster et al. 1994
,
Weaver et al. 1992
). This could help to explain the
apparent relationship between increased starch consumption and
diminished risk of colorectal cancer suggested by epidemiological
studies (Cassidy et al. 1994
). RS occurs for a number of
reasons (Annison and Topping 1994
), and evidence from
animal (Annison and Topping 1994
, Martin et al. 1998
) and human (Cummings et al. 1996
) studies
indicates that fermentation of different forms of RS may not lead
automatically to greater butyrate production. Moreover, examination of
the distribution of SCFA along the colon of pigs indicates that
different foods give individual profiles which may not be predictable
from fecal concentrations or pools (Marsono et al. 1993
,
Topping et al. 1993
). In the instance of rice, BR
increased the large bowel SCFA and digesta mass surpassing WR
or WR fed with an equivalent quantity of rice bran (Marsono et al. 1993
). More importantly, of these foods only brown rice
increased butyrate both overall and in the distal colon, the region at
greatest risk of noninfectious disease. This finding is consistent with
the lack of positive effect of adaptation to a WR diet on fecal indices
of bowel health in humans (Muir et al. 1998
). It was our
hypothesis that BR provided more RS, possibly as physically
inaccessible starch (RS1) and that this starch was reaching
the distal colon where it was undergoing fermentation in situ. The
present studies were designed to test that concept and whether rice
particle size influenced the concentration of starch entering the large
bowel of pigs. Additionally, we have determined the effects of diet on
large bowel calcium since fermentable carbohydrates, such as
oligosaccharides, may enhance its absorption from the large bowel
(Coudray et al. 1997
, Ohta et al. 1995
)
through greater generation of SCFA (Yanahira et al. 1997
).
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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Young adult male pigs of the Large White strain were used. All of the
animals were purchased from a commercial piggery (Millwards’ Piggery,
Eudunda, SA) and were ~14-wk-old at the start of the
experiment. The pigs were housed in temperature-controlled
individual pens with cement floors and were fed a standard pig
production diet as described previously (Topping et al. 1993
). All of the procedures described were approved formally
by the Animal Care and Ethics Committees of Division of Human Nutrition
and conformed to published guidelines (National Health and Medical Research Council, CSIRO and Australian Agricultural Council 1985
).
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Dietary Study |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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Pigs (n = 16) were used for this experiment and, after
a 2-wk adaptation period during which they were fed commercial pig food
(Pig Grower Pellets, Milling Industries, Murray Bridge, SA), they were
fed experimental diets comprised commercially-available
human foods. The diet was formulated from a range of foods and
ingredients (Table 1
) in proportions which mimicked the major contributors to that of
Indonesians (Marsono et al. 1993
). The diet provided
21% of energy as fat, 62% of energy as carbohydrate (of which 54%
was as starch) and 17% of energy as protein and supplied 33 g of
fiber/kg either as BR or rice bran. The WR and BR were cooked by
boiling 25-kg lots with sufficient water to hydrate them. The cooked
portions were then subdivided into quantities sufficient to provide
each pig with half of its daily ration and put into plastic bags for
storage at -20°C. The fish and meat were cooked in a microwave oven
in lots of ~500 g. Sufficient quantities of these and other dry
ingredients for half of the daily intake were weighed into plastic bags
for storage in sealed plastic ice-cream containers at -20°C. A
commercial pig vitamin and mineral supplement also was added to the
diet (Topping et al. 1993
). There were two groups, one
in which the diet contained parboiled brown rice (PBR, Sunbrown) as the
main starch source. In the other, the diet contained sufficient boiled
WR (Sunwhite) to provide the same amount of starch together with an
amount of heat-stabilized rice bran (Sunfarm) supplying an
equivalent amount of fiber as the brown rice of the other diet. All
rice products were donated by Rice Growers’ Co-operative (Leeton,
NSW). Isolated soy protein (PP 590) was produced by Protein
Technologies International USA, St. Louis, MO, and obtained
through Goodman Fielder Ltd. (Regency Park, SA). Casein was obtained
from Bonlac Foods Ltd. (Cheltenham, SA). Skinless and boneless white
fish was bought from Samtass Bros Seafoods (Richmond, SA). All other
ingredients were purchased locally though retail outlets. The pigs were
allowed free access to water throughout the day. For feeding, the
materials stored in the cold were allowed to thaw at room temperature
overnight or during the day before being mixed with water (1 L) and
presented. The pigs were fed the diet twice daily in two equal meals
given at 0830–0930 h and the second at 1530–1630 h. The meals were
prepared weekly, and then each pig was given sufficient food to provide
400 kJ/kg body weight (Brown et al. 1997
).
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The sampling procedures have been described in detail previously
(Brown et al. 1997
, Topping et al. 1993
).
Briefly, the pigs were fed the experimental diets for 3 wk. On d 7, 8,
14 and 15 after commencing this feeding program, total fecal output was
collected. Weighed subsamples for SCFA, pH and moisture were taken from
the first fresh fecal sample collected after morning feeding and the
remainder weighed and quickly frozen at -20°C. Samples for each day
were pooled, homogenized and a subsample freeze-dried for
determination of starch. At the end of the 3-wk feeding period, the
pigs were sedated with ketamine (Ketapex; Apex Laboratories, St.
Mary’s, NSW) and then anesthetized with halothane (Rhone Merieux, West
Footscray VIC) in O2. After a midline laparotomy, the
stomach and intestines were retracted and the esophagus and the rectum
were ligated and the whole gut excised. The cecum was tied off from the
terminal ileum and the whole large bowel separated from the mesentery
and laid out to approximately the same tension and measured. The cecum
was isolated and the colon divided into three sections of equal length
which were isolated with ligatures (starting at the proximal region).
These sections were numbered 1–3 from the proximal colon, and their
contents and that of the cecum were extruded manually into ice-cold
containers and weighed. The pigs were sampled 18 h after the last
evening meal. Four animals were sampled daily at 45-min intervals, and
the same sequence was maintained throughout the sampling period so that
a pig from each group was fed at 1500, 1545, 1630 and 1715 h and
sampled at 0900, 0945, 1030 and 1115 h.
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Cecostomized Pigs |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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Four pigs were fitted with a cannula in the cecum to allow continuous
sampling of gut contents as has been described previously
(Topping et al. 1997
). The pigs were anesthetized and,
when they were unconscious, a transverse incision was made on the right
flank behind the last rib. The cecum was carefully located and
cannulated with a silastic tube. The cannula was exteriorized dorsally
and anchored to a plastic plate with skin sutures and sealed with a
removable plastic plug. Of a 5 g/L solution of bupivacaine
hydrochloride (Marcain, Astra Pharmaceuticals, North Ryde, NSW), 2 mL
was used as a postoperative nerve block for pain relief on the dorsal
side of the incision followed by Finadyne (Flunixin, 50 g/L), Heriot
Agvet Pty Ltd., Rowville, VIC) for the following 2 d as required.
Recovery from surgery was rapid with pigs returning to normal food
intake within 2–3 d.
Feeding and sampling procedures.
The animals were maintained on pig rations and were fed daily at 900–1000 h. After complete recovery from the surgery (i.e. within 5–7 d), the pigs were fed one of four different diets for 8 d. These diets were similar to those used in the dietary study in that two contained cooked BR and WR + rice bran. In the other two diets the BR or WR was replaced, respectively, with equivalent amounts of either cooked brown rice flour (Sunblend BRF, Rice Growers’ Co-operative) or white rice flour (Sunblend 594 RF, Rice Growers’ Co-operative). The particle size of these flours was <0.5 mm. The intact rice grains were cooked by steaming but the fine rice flour was gelatinized by stirring with an excess of boiling water. On the last day of feeding these diets, digesta samples (~20 mL) were collected into ice-cold centrifuge tubes for determination of starch and SCFA. Samples were taken at 4, 6, 8 and 14 h after feeding and ~20 mL were blown into the tube before collection to ensure that they did not include material from the deadspace. There was a wash-out period of 6 d between each treatment.
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Analytical Procedures |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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) while a similar procedure was used
for their measurement in feces (Brown et al. 1997
).
Another aliquot was freeze-dried for moisture content and starch.
Fecal and digesta starch were measured as liberated glucose using a
commercial kit (#124-036 Boehringer Mannheim, Germany) after
amylase (Sigma Ltd., St. Louis, MO) and amyloglucosidase digestion
(Boehringer Mannheim). Samples of digesta from cannulated pigs were
similarly processed for determination of SCFA and starch. The calcium
content of digesta and diets was measured by atomic absorption
spectroscopy (Varian SpectrAA 400, Mulgrave, VIC 3170) by the method of
Capper and Tanner (1978)
. Briefly, samples were digested
with HClO4 and HNO3 (5:1, vol/vol) and the
residue taken up in demineralized water with KCl for analysis. A
certified sample of durum wheat (278 µg of Ca/g of wheat; National
Institute of Standards and Technology, Gaithersburg, MD) was analyzed
with each batch of samples and showed that recoveries were >95%. Statistical methods.
Values are presented as the means ± SE unless stated
otherwise. For the dietary study, effects of diet and week of sampling
(for fecal variables) or large bowel site were analyzed as a completely
random design using the General Linear Model of SAS (1996)
. Comparisons between means for groups fed BR and WR were
made within weeks or intestinal sampling site using the predicted
difference option of SAS (1996)
. Individual differences
at a time or sampling site were analyzed by ANOVA. Data obtained from
cecostomized pigs were analyzed similarly, examining for time and rice
type. A value of P < 0.05 was taken as the criterion
of significance.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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Food consumption and body weight gain. The pigs found both diets to be palatable and consumed the food promptly. Initial body weight was 36 ± 2 kg (n = 16) for both the PBR and WR groups. There was no difference in weight gain between the two treatments with corresponding final body weights of 49 and 52 kg (SE 3, n = 16).
Fecal weight, moisture, starch and pH.
There was a significant effect of time of feeding on fecal output
(Table 2
). Thus, the daily output of feces by pigs fed WR was constant for the
first 2 wk of the experiment. Output by pigs fed PBR was significantly
higher than that of pigs fed WR during wk 1 but by wk 2, output did not
differ between groups. Fecal water concentration was the same in both
groups of pigs during wk 1 and was unchanged in pigs fed WR during wk 2
(Table 2)
. Water concentration was significantly higher in feces from
pigs fed PBR than those fed WR during wk 2 (Table 2)
. There was a
significant effect of week of sampling and an interaction between week
of sampling and diet. Thus starch excretion was higher in pigs fed PBR
during wk 1, no change with time in pigs fed WR and a significant
decline in excretion in pigs fed PBR (Table 2)
. Fecal pH was higher in
the WR than in the PBR group at both sampling points (Table 2)
.
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). Output was constant in pigs fed WR but, as in the case of fecal output,
starch and pH, there was a significant effect of time in pigs fed PBR.
Thus, daily excretion of acetate, propionate and butyrate and of total
SCFA was significantly greater during wk 1 than wk 2.
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). There was a significant interaction between diet and sampling site with
significantly more digesta mass in the proximal colon of pigs fed PBR
than those fed WR. Digesta water concentration declined along the
length of the large bowel (Table 4
). As in the case of digesta mass, there was an interaction between diet
and sampling site with equal concentrations of water in the cecum and
distal colon but significantly more water in the proximal and mid
colon. The pH of cecal contents did not differ between the two
treatments but was lower in the PBR group at all other sites (Table 4)
.
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). The differences between the groups became larger along the colon. For
example, the difference in butyrate concentration between the two
treatments was 62% in the proximal colon and 263% in the distal
colon. Similar trends were seen for the pools (i.e. concentration
x digesta fluid volume) of total SCFA and of propionate and
butyrate as for their concentrations (Table 6
) with significant differences at all three colonic sampling sites.
However, this did not apply to acetate, the major SCFA, where pools
were significantly higher in pigs fed PBR only in the proximal and mid
colon.
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). Concentrations at all sampling sites were significantly lower in pigs
fed PBR than in those fed WR. Similarly, pools of calcium were lower
overall (P < 0.05) in the former pigs than in the
latter although at no specific site was the effect significant
(P > 0.05, Table 7
). However, the total pool
of calcium was 22% lower (P < 0.03) in pigs fed PBR
than in those fed WR.
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Starch and SCFA in cecal digesta.
Cecal starch concentrations were higher when the pigs were fed unmilled
WR or PBR compared with when they were fed these grains after milling
(Fig. 2
). There was no effect of time, but there was an effect of particle size
(pooled SE = 9.5, P < 0.01).
Concentrations were higher when the pigs were fed whole rice than fine
rice, but there was no effect of rice type (i.e., WR or PBR).
Concentrations of acetate, propionate or butyrate were unaffected by
time or rice particle size (data not shown).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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), in this
experiment we fed two main meals to conform more closely to perceived
human eating habits. The period (18 h) between the last meal and
sampling was necessitated by this feeding arrangement and the large
number of pigs which were sampled. It ensured also that there was
uniformity among the groups with no food in the small intestine. The
present data (and also those for colonic SCFA, pH and moisture) confirm
our earlier findings with similar diets fed as one meal a day with
higher values in the proximal and median colon of pigs fed PBR
(Marsono et al. 1993
). We had hypothesized that the
differential effect of BR in raising large bowel digesta and SCFA was
due to provision of more RS leading to greater colonic fermentation.
The greater fecal excretion of starch and SCFA in pigs fed PBR in wk 1
of the experiment support that proposition. However, by wk 2, both
stool mass and fecal starch excretion had declined in pigs fed BR and
did not differ between groups. As in the earlier report (Marsono et al. 1993
), the pigs found both of the diets to be highly
acceptable from the outset and the food was eaten promptly throughout
the experiment so that the change in the BR group is unlikely to
reflect any difference in food intake. One possible reason for the
diminished excretion is adaptation in the colonic microflora with an
increased capacity of the colonic microflora to metabolize starch. This
would explain the lower fecal starch values in wk 2 of the experiment
and also the higher SCFA availability.
It had been expected that some of the greater digesta mass in
pigs fed PBR was starch but analysis of the large bowel contents showed
that while starch was higher in pigs fed PBR, the total large bowel
pool was only 3.61 g (as opposed to 1.46 g in pigs fed WR).
These data are consistent with those for fecal starch, but the absolute
quantities cannot explain the large difference in between
digesta wet weight between the groups. Furthermore, despite these
substantial differences, digesta dry weight in the proximal and mid
colon did not differ between treatments. Inter alia, these data
suggest that the difference between PBR and WR groups could reflect
more bacteria in the proximal colon of pigs fed the former diet. This
would be expected from greater entry of starch into the large bowel
which would enable greater fermentation. There is some evidence to
support this possibility. Studies with rats fed polished (i.e., white)
rice with an antibiotic showed much greater fecal starch excretion and
lower serum SCFA than those not fed the antibiotic (Cheng and Yu 1997
). Kleessen et al. (1997)
found greater
numbers of culturable bacteria in rats fed RS1 and
RS2, consistent with the present data. The greater moisture
content of digesta from pigs fed PBR also coincides with more
bacteria. However, possibly some of the difference between treatments
was due to water-holding by NSP present in PBR. This presupposes a
difference in their fermentability in BR and rice bran which remains to
be determined. The concentrations of enzyme-resistant starch in the
Australian rice products used in these experiments are low
(Marsono and Topping 1993
) so the difference in large
bowel fermentation between PBR and WR is due to other factors. One of
these could be particle size. The pig is considered to be a good model
species for human fiber metabolism (Graham and Aman 1982
) despite the fact that the large bowel is a rather greater
fraction of total gut volume than in humans (van Soest 1995
). However, one important difference between pigs and
humans is that pigs bolt (rather than chew) their food so that the
individual variation due to mastication performed by humans is
lessened. However, chewing influences food particle size which is an
important determinant of gut transit, with smaller particles moving
more slowly than larger ones (Heller et al. 1980
). Also,
particle size is a major influence on digestibility with smaller
particles being more susceptible to enzyme hydrolysis in vitro
(Heaton et al. 1988
) and in vivo (Muir et al. 1994
). In earlier studies with pigs, rice grains were seen in
the proximal colon (Marsono et al. 1993
), indicating
their passage through the small intestine. Entry of starch into the
large bowel was shown in the present studies in cannulated pigs where
digesta starch concentrations were substantially higher after PBR and
WR consumption than after the diets were milled. However, the
increase was the same in pigs fed either the whole WR or BR diets. Due
to a lack of a suitable digestibility marker, it was not possible to
calculate the total pool of starch. Nevertheless, these data indicate
that particle size may have been an important determinant of the small
intestinal digestibility of starch.
These data leave open the question of the factor(s) which affect RS in
rice and the distribution of the fermentation products along the colon.
The profiles of SCFA and digesta were similar in both groups (i.e.,
high in the cecum and proximal colon and falling toward the distal
colon). These are consistent with previous findings in this species
made by ourselves (Marsono et al. 1993
, Topping et al. 1993
) and others (e.g., Bach-Knudsen et al. 1993
, Martin et al. 1998
). This distribution
profile for SCFA resembles that in human surgical patients with
colostomy (Mitchell et al. 1985
). Higher SCFA and
digesta in the proximal large bowel coincide with increased
fermentation through greater substrate availability while the lower
values in the distal colon are consistent with substrate depletion and
absorption of SCFA and water. As noted previously (Marsono et al. 1993
), the mass of digesta was significantly greater in
pigs fed PBR than in those fed WR. However, in this experiment,
differences were not seen in the distal region, possibly due to the
changed feeding schedule which could allow greater efficiency of
fermentation of smaller meals. If this is the case, the pattern of
feeding could be an important determinant not only of fermentation but
of the distribution of the products along the large bowel. This, and
the low levels of RS and NSP in WR may also account for the lack of
effect of a simulated Chinese-style diet based on rice on
indicators of bowel health in humans (Muir et al. 1998
).
As reported earlier (Marsono et al. 1993
), total and
individual SCFA were distributed similarly along the large bowel in
both groups, but their concentrations and pools were higher at all
sampling points (except in the cecum) in pigs fed BR. The absence of
any difference in the cecum is similar to the data obtained over an
extended time period of sampling in cannulated pigs which showed no
effect of rice type or particle size on SCFA concentration. Comparable
results were obtained by Fleming et al. (1989)
in pigs
with cecal cannulae which had been fed beans. It appears that
nutritional influences on SCFA become manifest in the proximal colon
and that diet and food composition determine the distribution of SCFA
from that point along the colon. The speed of fermentation may be one
factor responsible for the greater availability of SCFA (especially
butyrate) in the distal colon. Studies in vivo (Topping et al. 1997
) and in vitro (Christl et al. 1997
) with
high amylose starches have suggested that their bacterial fermentation
is rapid. If this metabolism were very fast, then SCFA might be
produced (and absorbed) in the proximal colon and not reach the distal
colon. This could account for the findings of Tomlin and Read (1990)
who found a substantial increase in breath
H2 evolution in humans following RS consumption (consistent
with greater colonic fermentation) but no change in fecal variables.
Pharmacological manipulation of transit can alter fecal SCFA in humans
without any apparent change in production (Lewis and Heaton 1997
). PBR should be fermented more slowly than WR due
to the presence of the bran layer and the rather higher starch values
in pigs fed the former support this. Thus, the rate of fermentation
relative to transit factors could control the supply of SCFA to the
distal colon and their subsequent fecal appearance. The distal colon is
the major site of noninfectious large bowel disease in humans and
limited availability of SCFA could contribute to this risk. Of the
three major SCFA, the pools of propionate and butyrate were higher in
the distal colon of pigs fed BR. Evidently, this could be an advantage
in promoting bowel health in this region where SCFA availability is
lowest. Further studies with suitable markers, including determination
of digestibility and rate of passage, are required to clarify this
issue.
SCFA have trophic effects on the large bowel. Studies in rats have
shown that increased dietary intake of fermentable carbohydrates
increases the volume and weight of the cecum and its contents (e.g.,
Goodlad and Mathers 1990
, Reimer and McBurney 1996
). Adaptation to dietary NSP increases the mass of the
colon in pigs (Pond and Varel 1989
) and its mass and
length in rats (Reimer and McBurney 1996
) under
conditions where greater SCFA production and digesta mass were to be
expected. Feeding of high amylose starch results in a
dose-dependent increase in colon length in pigs (Topping et al. 1997
) which is consistent with those other data. However,
in this study there were no differences in large bowel length or weight
between the two groups which is rather unexpected if large bowel SCFA
concentrations and digesta mass were major determinants for large bowel
growth. There may be differences between RS from different
sources in their actions on these variables. This proposition is
supported by the report of Heijnen and Beynen (1997)
which showed that the excretion of nitrogen in the urine or feces
differed according to the type of RS which was fed. It is possible also
that the length of the experiment may have been too short to show any
effect on large bowel length, but this seems unlikely because effects
of the high amylose starch were seen after a similar time interval.
Recent data suggest that the intake of fermentable carbohydrates
increases the absorption of calcium in the large bowel of rats
(Ohta et al. 1995
) and humans (Coudray et al. 1997
), possibly through greater production of SCFA
(Yanahira et al. 1997
). Large bowel SCFA absorption is
accompanied by that of water and cations, and their infusion into the
rectum of humans leads to greater apparent uptake (Trinidad et al. 1997
). However, the fact that rats practice fecal
refection, which can modify SCFA production (Jackson and Topping 1993
), means that data on calcium status from this species are
not directly applicable to humans. The present data from pigs
that large bowel calcium concentrations and pools declined along the
colon and calcium levels were lower in those fed PBR (where SCFA were
higher) than in those fed WR. While the pigs drank tap and not
demineralized water, there was no evidence that water consumption was
different between the two groups. Analysis of PBR, WR and rice bran
(Record, I. R., unpublished observations) shows that the intakes
of calcium would be similar in the two groups. Thus, these data provide
support for a role of fermentation through greater production of SCFA
in promoting the uptake of calcium from the large bowel of pigs. In
conclusion, these data confirm that feeding PBR increases large bowel
digesta mass and fecal SCFA relative to WR plus rice bran when fed at
the same level of dietary fiber. The increment appears to be due to
greater RS in PBR, but this does not explain the greater mass of
digesta in pigs fed PBR. Bacterial proliferation appears to be one
explanation, but this remains to be confirmed. Greater availability of
SCFA in pigs fed PBR appeared to lower colonic calcium which may be of
benefit in enhancing calcium absorption in humans and other monogastric
species.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Presented in part in preliminary form at the 21st Annual Scientific Meeting of the Nutrition Society of Australia, Brisbane, Queensland, 1997 [Bird, A. R., Illman, R. J., Hayakawa, T. & Topping, D. L. (1994) Brown rice increases fecal and large bowel short-chain fatty acid levels in pigs. Proceedings 21, 135].
3 Department of Food Science, Faculty of Agriculture, Gifu University, Gifu 501-11, Japan.
4 Pusat Antar Universitas Pangan dan Gizi, Universitas Gadjah Mada, Yogyakarta, Indonesia.
5 Department of Animal Science, University of Sydney, Camden NSW 2570, Australia.
6 CSIRO Mathematical and Information Sciences, Glen Osmond, SA 5064.
8 Abbreviations used: BR, brown rice; BRF, brown rice flour; NSP, nonstarch polysaccharides ("fiber"); PBR, parboiled rice; RS, resistant starch; SCFA, short-chain fatty acids; WR, white rice; WRF, white rice flour.
Manuscript received November 30, 1999. Initial review completed January 5, 2000. Revision accepted March 27, 2000.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODSDietary StudyCecostomized PigsAnalytical ProceduresRESULTSDISCUSSIONREFERENCES |
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1. Annison G., Topping D. L. Resistant starch: Chemical structure vs. physiological function. Ann. Rev. Nutr. 1994;14:297-320[Medline]
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