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Journal of the American College of Nutrition, Vol. 27, No. 1, 102-108 (2008)
Published by the American College of Nutrition

Supplementation of Konjac Glucomannan into a Low-Fiber Chinese Diet Promoted Bowel Movement and Improved Colonic Ecology in Constipated Adults: A Placebo-Controlled, Diet-Controlled Trial

Hsiao-Ling Chen, PhD, Han-Chung Cheng, MS, Wen-Tsu Wu, MS, Yann-Jiu Liu, MS and Su-Yuan Liu, MS

Institute of Nutritional Science, Chung Shan Medical University, Taichung (H.-L.C., H.-C.C., W.-T.W., Y.-J.L., S.-Y.L.)
Department of Nutrition, National Cheng Kung University Hospital, Tainan (Y.-J.L.), TAIWAN

Address reprint requests to: Dr. Hsiao-Ling Chen, Professor, Chung Shan Medical University, No. 110, Sec. 1 Chien-Kuo N. Road, Taichung, TAIWAN 402. E-mail: hlchen{at}csmu.edu.tw


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Objectives: This diet-controlled study was designed to examine effects of konjac glucomannan (KGM) supplement on the bowel habits and colonic ecology in 7 constipated subjects. In addition, the mechanisms by which KGM modulated the bowel habit were explored.

Methods: Seven constipated subjects who passed bowel movement less than once a day participated in this diet-controlled linear study that consisted of a 21-d placebo period, a 7-d adaptation period, and a 21-d KGM-supplemented (1.5 g, tid) period. The large bowel response and fecal characteristics were recorded daily. Stools were collected individually on days 15–21 of placebo and KGM periods for analyses of colonic ecology indices such as fecal microflora, pH and short chain fatty acid content. Fecal component was determined to illustrate the fermentation of KGM.

Results: KGM supplement slightly but significantly increased the weekly defecation frequency from 4.1 ± 0.6 to 5.3 ± 0.6 and slightly eased the bowel movement. The fecal wet weight (g/d) and percent moisture were not significantly altered with the fiber supplement. However, the dry fecal weight (g/d) was increased mainly in the soluble mass. KGM supplement increased the fecal concentration (log counts/g wet feces) of lactobacilli, and the daily output (log counts/d) of bifidobacteria, lactobacilli and total bacteria in this diet-controlled study. In addition, fermentation of KGM resulted in greater fecal acetate, propionate and i-butyrate concentrations and lower fecal pH.

Conclusion: The modest dose of KGM supplement promoted bowel movement by 30% and improved colonic ecology in constipated adults.

Key words: glucomannan, constipated, microflora, short chain fatty acid, bowel movement

Abbreviations: KGM = konjac glucomannan • SCFA = short chain fatty acid


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Konjac glucomannan (KGM) is a hydrophilic soluble fiber derived from the tuber of Amorphophallus konjac C. Koch [1]. KGM has traditionally been consumed as rubbery jelly, noodles, and other food products in Asia for centuries. Recently, KGM has been found to be a potential adjunct for glycemic control and a hypocholesterolemic reagent [2,3]. The action of glucomannan in the bowel has also been evaluated in several clinical studies. KGM (1 g, tid for 10 d) normalized the small bowel transit time in 13 adult patients affected by chronic idiopathic constipation as compared to the age, sex and dietary habit-matched controls [4]. KGM (100 mg/kg, bid for 12 wk) increased stool frequency and reduced the use of enema in children with severe brain damage and chronic constipation of bowel movement [5]. Another open, non-controlled, multi-center study observed a beneficial effect of glucomannan (1 g, tid for 1 month) in 93 people aged 14 and over who passed three or fewer bowel movements per week [6]. Although these previous studies suggest KGM supplement may relieve constipation in patients who infrequently passed stools, it is unclear whether KGM supplement would benefit adults whose constipation was not as severe.

KGM has been shown to act as a prebiotic fiber in animals [7,8]. However, this prebiotic effect has not been shown in humans. Recent findings suggest that supplementation of certain bifidobacteria and lactobacilli promote bowel movement, particularly in constipated humans [9,10]. Therefore, KGM supplement may beneficially modulate colonic microflora and ecology in humans, which in turn further promote bowel movement. Furthermore, KGM may increase stool weight by promoting fecal bacterial mass and its accompanying moisture [11]. The mechanical action of KGM itself and end products of fiber fermentation may also stimulate colonic motility [11].

This study was aimed to evaluate effects of modest dose of KGM supplement on bowel habits and colonic ecology in slightly-constipated adults. In addition, fecal components were determined to illustrate the metabolism of KGM.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Subjects
Adult volunteers who passed bowel movements less than once per day or had straining with passage of bowel movement were defined as constipated. We recruited constipated people from out-patient clinics of the National Cheng Kung University Hospital whose constipation had lasted for more than 6 months. None of the recruits used laxatives or enema. Criteria for exclusion were neo-menopausal or postmenopausal, self-reported lactose intolerance, vegetarian, habitual consumption of lactic acid bacteria-containing food, any current perception of large bowel disease such as inflammatory bowel disease and colon cancer, history of neurological incidence, and unwillingness to follow a specified diet. Although the study was open to men and women, only female subjects met all the criteria. During an initial interview, participants were asked to complete a questionnaire regarding their bowel movements and stool consistency. Participants were asked to keep a 3-d dietary record, from which we designed their diet and evaluated compliance, reliability, and attitude. Seven women participated in this study after having given formal consent. Relevant characteristics of the women are shown in Table 1.


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  		Table 1. Basic Characteristics of Constipated Subjects before Entering the Study

 
Experimental Design
This single-blind, placebo-controlled, diet-controlled linear study consisted a 3-wk placebo period, a 1-wk adaptation period, and a 3-wk KGM period (1.5 g KGM/meal, 4.5 g/d) period. Throughout the study, volunteers consumed a controlled diet and 3 gelatin capsules each containing either 0.5 g corn starch as a placebo or 0.5 g KGM powder (catalogue no. T18, < 60 mesh, Fukar International Company, Taipei, Taiwan) with 150 mL water at each meal. The composition of the konjac powder was 80.0% glucomannan, 8.0% starch, 3.4% protein, 3.8% lipid, 1.7% ash and 3.1% moisture, determined using methods as described previously [2]. The dose of KGM gradually increased during the adaptation period from 1.5 g/d (d 1–3) to 3.0 g/d (d 4–7) and was maintained at 4.5 g/d throughout the KGM period. This dose was chosen because results from previous studies indicated that 3–5 g/d was effective in modulating bowel habit [4–6]. Our previous work also indicated that this dose was safe and effective in modulating blood sugar fluctuations in Taiwanese adults [2]. Seven day cycle menus of typical Chinese food were provided to subjects throughout the study in order to rule out dietary variations that may have confounded the effect of KGM on bowel habit and colonic ecology. Energy and dietary fiber provided by the experimental diet was designed to meet individual's regular intake based on the diet record volunteers had made in the run-in period. Macronutrient composition (carbohydrate 50.5%, protein 15.2%, fat 35.0%) was designed to mimic the typical dietary pattern of Taiwanese adults [12]. Nutrients and energy intakes were calculated using local nutrient composition tables [13]. Subjects were not allowed to consume any additional food. In addition, subjects were advised to maintain their daily physical activity, life style and sleeping habits. Capsule consumption, an index of subject compliance, was verified daily when empty packets were exchanged for the next day's supplements.

The gastrointestinal response including ease of bowel movement, feeling of complete relief, abdominal cramping, borborygmi, bloating, flatulence, and the stool consistency were recorded and checked by the investigators daily. Stools were collected individually in plastic bags on d15–21 of placebo and KGM periods to determine the fecal weight, composition, microflora, pH and short chain fatty acid (SCFA) contents. The experimental protocol was approved by the Committee on Human Study of the Chung Shan Medical University Teaching Hospital. All subjects gave their written informed consent.

Defecation Frequency, Gastrointestinal Response and Stool Consistency
The frequency of bowel movement was recorded and gastrointestinal response was graded in a daily chart. The ease of bowel movement was graded as 1 (easy), 2 (slightly difficult), 3 (difficult), and 4 (extremely difficult). Feeling complete relief was graded as 1 (extremely agree), 2 (agree), 3 (disagree) and 4 (extremely disagree). The side effects such as abdominal cramping, borborygmi, bloating, and flatulence were graded daily from 0 (no symptom), 1 (very slight symptom), 2 (slight symptom), 3 (severe symptom), and 4 (very severe symptom). The stool consistency was graded from 1 (very hard), 2 (hard), 3 (soft), 4 (very soft), to 5 (watery) whenever bowel pass occurred.

Fecal Weight, Moisture and Preparation of Fecal Composite
Feces were collected in individual plastic bags and immediately sent to the laboratory in an ice bucket and weighed. Aliquots (1%) of fresh feces were then taken from the center, blended with equal volume of distilled water (1:1 w/v) and centrifuged at 8000 g for 10 min at 25°C. The pH of the supernatant was measured using a pH electrode and the remaining?feces stored at –80°C. Feces excreted during d15–21 from one individual were pooled as a fecal composite for further analysis. The fecal moisture content was determined by comparing the wet and dry weights of samples.

Fractionation of Fecal Samples
The dual-screen procedure developed by Chen et al. [14] to separate plant, bacterial and soluble matter in feces was modified for this study. In brief, duplicate dry fecal composite (1 g) was mixed with distilled water (1:120 w/w) at 60°C for 10 min and subjected to centrifugation at 8000 g for 10 min at 25°C. The pellet was then dispersed in 60 mL distilled water and was blended for 6 min in a stomacher, followed by centrifugation at 8000 g for 10 min at 25°C. The supernatants were pooled together and lyophilized to be the soluble fraction. The resultant pellet was blended with an aqueous solution of 0.1% sodium lauryl sulfate (SLS; 60 mL) and filtered through a 150-µm screen. The residue on the screen was dispersed and rinsed with water until the foaming of the SLS in the sample disappeared. The residue was blended with 60 mL SLS twice more. The pooled filtrate that passed through the 150-µm screen was then passed through a 25-µm nylon screen to remove the small plant residue. The residue on the 25-µm nylon screen was added with SLS solution (60 mL) and subjected to the blending and filtration twice more. The filtrate that passed through the 25-µm nylon screen was pooled and an aliquot was taken to determine the fecal microflora. The filtrate was then centrifuged at 8000 g for 10 min at 25°C. The resultant pellet (bacterial fraction) was rinsed with 20 mL water, centrifuged, and lyophilized. The final residue on the 150-µm and 25-µm screens was rinsed with 20 mL water, pooled and lyophilized to be the plant fraction.

Quantification of Fecal Total Bacteria, Bifidobacteria, Lactobacilli, Bacteroides and Clostridia
Changes in fecal bacterial population were assessed using fluorescence in situ hybridization method (FISH). Genotypic probes targeting 16S rRNA of bacteria were manufactured and tagged with fluorescent markers, which allowed fecal bacterial populations to be quantified with a fluorescence microscope [15]. The probes used were Bif164 (5'-CAT CCG GCA TTA CCA CCC-3'), Laal (5'-CAT CCA GTG CAA ACC TAA GAG-3'), Bac303 (5'-CCA ATG TGG GGG ACC TT-3'), and Ib1 (5'-GAT GGA ACT GTA ACA AAA CT-3'), specific for bifidobacteria [15], lactobacilli [16], bacteroides [17] and clostridia [18], respectively. The nucleic acid stain 4', 6-diamidino-2-phenylindole (DAPI) was used for total bacterial counts. Fixation and hybridization of fecal bacteria were done following the method described by Jansen et al. [15]. However, we used bacterial solution obtained from the fecal fractionation, instead of crude fecal solution used by Jansen et al. [15]. Aliquots (5 µL) of fecal bacterial samples were fixed on wells of microscopic slides. Probes (final concentration 25 nmole/L) in hybridization mix (20 mmole/L Tris-HCl, 0.9 mole/L NaCl, 3.5 mmole/L SDS, pH7.2) were added to wells and reactions were allowed to take place at 50°C for 16 h for bifidobacteria, lactobacilli and clostridia, and for 5 h for bacteroides in humid chambers. After rinsing in preheated washing buffer (20 mmole/L Tris-HCl, 0.9 mole/L NaCl, pH7.2) at 50°C for 30 min, slides were air-dried in a dark room. To quantify the total fecal bacteria, slides were incubated with DAPI solution (1.4 mmole/L) for 10 min, followed by washing with preheated washing buffer (50°C) for 10 min and air-dried. Probe fluorescence was detected with a Zeiss Axioskop2 microscope (Carl Zeiss, Jena, German) fitted for epifluorescence microscope with a 100 W mercury bulb (HBO 103), a 20x Plan-neofluar objective, a filter set 01, 09 and 20, and a cooled charge-coupled device (CCD) video camera (MacroFire, Model S99831, Optronics, Goleta, CA). The microbial counts are expressed as log10 counts/g wet feces.

Fecal SCFA Content
Aliquots (0.5 g) of fecal composite were analyzed for acetate, propionate, i-butyrate and n-butyrate with 4-methyl-n-valeric acid as an internal standard, as described previously [19]. The SCFA extracted from fecal samples were dissolved in 10% orthophosphoric acid solution immediately before they were injected onto a gas chromatography (GC-14B, Shimadzu, Tokyo, Japan) fitted with a glass capillary column (0.25 mm, 30 m Stabilwax-DA, Restek Corp., Bellefonte, PA) and a flame ionization detector. The initial temperature of the oven was 100°C and this was raised to 200°C at 6°C/min. The temperature of the injection port and detector was 250°C, respectively. The flow rate of carrier gas, N2, was adjusted to be 1 mL/min. Peak areas were analyzed with C-R6A Chromatopac (Shimadzu Corp., Tokyo, Japan).

Statistical Analysis
Data are expressed as means ± SE. All data were analyzed using SPSS for Windows (Version 10.0). The concentrations of fecal bacteria were log transformed. All parametric data (fecal weight, moisture, fecal pH, SCFA, and log-transformed bacteria) were compared using paired t test. The defecation frequency, scales for gastrointestinal response and stool consistency between the 3rd wk of placebo period and each time point of KGM period were undertaken with the Wilcoxon matched pairs test. Differences were considered significant at p < 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Subjects took 99.5% and 98.2% of capsules given in the control and KGM period, respectively, as calculated by the returned capsules. All of the subjects completed the fecal collection and blood draws throughout study.

Defecation Frequency, Gastrointestinal Response and Stool Consistency
The mean frequency of defecation was significantly raised at the 2nd and 3rd wk of the KGM period as compared to the 3rd wk of the placebo period (Table 2). Of the 7 participants, one woman increased her stool frequency by 4 stools/wk whilst five others increased their stool frequencies by 1–2 stool/wk. KGM supplementation did not ease the passage of bowel movements in these constipated women until the 3rd wk of KGM period. At this time, KGM supplementation decreased the ease of passage rating by 1.7 in one woman, by 0.75 in another, and by 0.3–0.5 in five other women. None of these women felt complete relief after passage at the end of the placebo period. However, KGM supplement decreased this rating by 1.25 in one woman and by 0.5–0.7 in three women. KGM supplementation reduced borborygmi, but not abdominal cramping and bloating at the 3rd wk of the as compared to the 3rd wk of the placebo period. Although the average symptom of flatulence increased slightly at the end of KGM period, KGM actually decreased flatulence in three subjects and increased flatulence in another three subjects. KGM supplementation did not significantly soften the feces; only one subject rated softer stools by more than 0.5 on the scale at the 3rd wk of KGM period.


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  		Table 2. Large Bowel Response at the 3rd Wk of the Placebo and during the KGM Period in Constipated Subjects1

 
Fecal Weight and Percent Moisture
Fecal wet weight and percent moisture content were not significantly affected by the KGM supplementation (Table 3). Fecal dry weight was greater by 3.6 ± 1.3 g/d during the supplementation period compared with the placebo period. The increase in the fecal dry mass was mainly due to increases in the fecal soluble fraction of 2.5 ± 0.9 g/d. The relative proportions (% of fecal dry mass) of plant and bacterial fractions was 18.8 ± 3.1% and 42.4 ± 2.6% in the placebo period, respectively, which did not differ from 18.1 ± 2.7% and 40.6 ± 2.9% in the KGM period. However, KGM supplement significantly increased the relative proportions (% of fecal dry mass) of soluble fraction from 29.2 ± 2.5% in the placebo period to 34.6 ± 2.9% in the KGM period.


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  		Table 3. The Weight and Moisture Contents of Stools Collected from Constipated Subjects During Days 15–21 of the Placebo and KGM Period1

 
Fecal Microflora
Total bacterial concentration (log counts/g wet feces) did not vary with KGM supplement (Table 4). However, there was a higher concentration of fecal lactobacilli after consumption of KGM supplement. Furthermore, KGM supplement effectively increased the numbers of bifidobacteria, lactobacilli and total bacteria in the daily fecal output. KGM also beneficially increased the relative proportions (% of total bacteria) of bifidobacteria and lactobacilli and decreased the relative proportion of clostridia compared with the placebo.


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  		Table 4. Fecal Microflora of Constipated Subjects during Days15–21 of the Placebo and KGM Period1

 
Fecal pH and SCFA
KGM supplement significantly lowered the fecal pH. In agreement with that, KGM supplement increased the fecal concentrations of acetate, propionate, i-butyrate and total SCFA as compared with those in the placebo period (Table 5). In addition, KGM supplementation increased the daily fecal output of acetate, propionate, i-butyrate, and total SCFA. The relative proportion of propionate to total SCFA increased during the KGM period compared with the placebo period while the proportions of other SCFAs did not change with the KGM supplement.


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  		Table 5. Fecal pH and Short Chain Fatty Acids (SCFA) during Days 15–21 of the Placebo and KGM Periods1

 

   DISCUSSION
 
This study demonstrated 2 beneficial aspects for adding KGM (4.5 g/d) into a low-fiber diet in constipated adults. Firstly, this dose of KGM powder was well tolerated and increased stool frequency in 6 of the 7 participants by at least 1 stool/wk. Secondly, KGM improved colonic ecology by decreasing fecal pH, increasing the relative proportions of bifidobacteria and lactobacilli, and reducing the proportion of clostridia in feces.

In this experiment, we observed increased bowel movement frequency during the run-in period. Since dietary fiber offered in the experimental diet did not exceed what was usually consumed in the run-in period, this discrepancy may be due to differences in the method of data collection. The numbers of bowel movements during the study were recorded daily using gastrointestinal-response charts, which were considered to be more accurate than the recall data collected during the run-in period.

Although KGM supplementation promoted defection frequency by ~30%, from 4.1/wk to 5.3/wk, this effect was not as pronounced as that reported for severely constipated patients where increases from ~2 to ~4 stools per wk were found [6]. The severity of constipation of subjects was different between our study and the previous study, which could cause differences in KGM's laxative effect. On the other hand, this study observed that KGM supplement beneficially decreased the difficulty at evacuation and reduced the severity of borborygmi, which agreed with what were observed in severely-constipated patients [6].

There was a tendency for KGM supplementation to increase fecal wet weight, an effect that could have contributed to the recorded increase in bowel movement frequency. KGM also caused a significant increase in daily fecal dry weight (3.7 g/d) that was mainly due to the fecal soluble material, instead of plant material. Since these subjects consumed controlled 7-d cycled diets all through the study, we based on the gravimetric recovery of fecal component on two suggestions. Firstly, the large viscous KGM polymer that was unable to pass the 25 µm fractionation screen was degraded to small water-soluble glucomannan in the colon. Secondly, the increased fecal soluble material was partially due to the increased SCFA production. These suggestions were supported by a previous in vitro study that indicates KGM can be degraded by human fecal enzymes and therefore result in SCFA production [20]. In addition, the gravimetric mass of fecal bacteria only tended to increase with KGM supplement in this study, which agreed with the total bacteria counts. Since KGM metabolites do not contribute significantly to fecal bulk and fecal bacterial mass did not increased dramatically, KGM supplement did not increase the fecal bulk significantly.

In agreement with previous animal studies [7,8], this study demonstrated that KGM acted as a prebiotic fiber and selectively stimulated the growth of bifidobacteria and lactobacilli in constipated adults. Increases in colonic bifidobacteria and lactobacilli by KGM has been found to promote bowel movement [9,10].

The colonic ecology was improved with KGM supplement as the proportion of fecal clostridia population and fecal pH decreased. The mechanisms by which clostridia was suppressed could have been increases in acidic fermentation products and secretion of antimicrobial substances by bifidobacteria and lactobacilli [21]. Furthermore, an in vitro study demonstrated the konjac fluid prevents the growth of food-born Clostridium perfringens [22], implying that glucomannan per se could directly suppress the colonization of these bacteria in the intestine. Therefore, KGM could beneficially suppress the growth of clostridia in the human colon indirectly through the action of bifidobacteria or directly through its own physicochemical characteristics. KGM supplement did not reduce the fecal bacteroides concentration, which agreed with the effect of 10% KGM diet in mice [8]. KGM supplementation may be protective to the human colon. Enhancing the colonization of lactic acid bacteria has been found to inhibit the occurrence of carcinogen-induced colon cancer in rodents [23–26] and to facilitate apoptotic deletion of carcinogen-damaged colon cells [27]. In addition, KGM supplementation increased fecal SCFA concentration, which led to lower fecal pH. An inverse correlation between stool pH and colon cancer risk has been observed [28,29]. Therefore, metabolism of KGM improved colon ecology.


   CONCLUSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 CONCLUSION
ACKNOWLEDGMENTS
 REFERENCES
 
This study demonstrated that addition of a modest dose of KGM (4.5 g/d) into low-fiber diets increased bowel movement frequency by 30% and improved the colonic ecology in slightly-constipated adults.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 CONCLUSION
 ACKNOWLEDGMENTS
REFERENCES
 
We thank Dr. Ju-Hsuen Wang, Department of Medicine in the National Cheng Kung University Hospital, for assistance in recruiting subjects. This work was supported by the National Science Council Grant NSC 93-2320-B-040-043, Taipei, Taiwan.

Received February 8, 2006. Accepted November 1, 2006.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES
 

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