First draft prepared by P.J. Abbott

    Food Science and Safety Section, National Food Authority, Canberra,


    Biological data

         Biochemical aspects
              Digestion in the small intestine
              Fermentation in the large intestine
              Human studies
              Metabolism of fermentation end-products

         Toxicological studies
              Short-term toxicity
              Long-term toxicity
              Special studies: Nutrient absorption

         Observations in humans
              Vitamin absorption
              Cholesterol absorption





         Konjac flour was previously considered by the Committee at its
    forty-first meeting (Annex 1, reference 107), when it allocated a
    temporary ADI 'not specified' on the basis of the available data on
    toxicology, particularly from human studies, the long history of use
    of konjac as a food in China and Japan, and estimates of consumption
    in traditional and anticipated uses. The results of additional
    short-term studies of toxicity, which the Committee was informed had
    been conducted in rats and dogs, together with adequate data on the
    fate of konjac flour in the gut and information on its influence on
    the bioavailability of fat-soluble vitamins were requested for review
    by 1996.

         At its present Meeting, the Committee considered some additional
    data on the fate of konjac flour in the large intestine, including a
    recent study with human faecal flora  in vitro. The likely
    fermentation end-products were also identified. Additional short-term
    studies were considered, including a 28-day study on the effect of 10%
    konjac flour on protein digestion and absorption in rats, and a
    12-week study on the hypocholesterolaemic effects of konjac flour in
    rats. The other short-term toxicity studies in rats and dogs referred
    to previously (Annex 1, reference 107) were not available. An
    additional long-term study in rats on the effects of konjac flour on
    calcium and phosphorus metabolism and on tissue senescence was
    considered. Two additional genotoxicity studies on konjac flour were
    also available. With regard to the effect of konjac flour on the
    availability of fat-soluble vitamins, data from studies in animals and
    humans on the effect of konjac flour and other polysaccharide gums on
    vitamin and cholesterol absorption were reviewed, and a rationale was
    presented for a threshold dose for inhibition of absorption by konjac


    2.1  Biochemical aspects

         Konjac flour is a high-relative-molecular-mass, linked, linear
    copolymer of glucose and mannose ('glucomannan'), in which D-glucose
    and D-mannose are linked by -1,4 glycosidic bonds in a molar ratio of
    1:1.6. Branching from the C3 of either hexose is estimated to occur
    every 10 repeating units through -1,3 linkages, and acetyl groups are
    bound every 9-19 units, contributing to the high solubility of konjac
    flour in water. Thus, while konjac flour is a polysaccharide gum, it
    is considered to be soluble as a result of its ability to form a
    solution of very high viscosity in water (Jenkins  et al., 1986;
    Nishinari  et al., 1992).

    2.1.1  Digestion in the small intestine

         The indigestibility of konjac flour in the small intestine was
    demonstrated in an experiment in which a pancreatic enzyme preparation
    was unable to release glucose from  konnyaku, a konjac flour
    preparation (Inoue, 1942). There are no known digestive enzymes that
    cleave the -1,4 linkages between the glucose and mannose units of the
    polysaccharide backbone or the -1,3 linkages at the branch point. If
    any acid or enzyme-catalysed hydrolysis occurs, the only breakdown
    products would be D-glucose or D-mannose.

    2.1.2  Fermentation in the large intestine

         While there is no mammalian enzyme-catalysed hydrolysis of konjac
    flour in the intestine, depolymerization to a variety of glucomanno-
    oligosaccharides can occur in the large intestine as a result of the
    action of intestinal microflora (Maeda, 1911; Inoue, 1942; Jenkins
     et al., 1986). Enzymes with -mannanase and cellulase activities
    which are capable of depolymerizing glucomannan have been detected in
    a variety of microorganisms of different origins (Akino  et al.,
    1987; Yoshida & Morishita, 1991; Araki  et al., 1992), including
    faeces (Inoue & Inoue, 1956). The extent of depolymerization of
    polysaccharide gums and the subsequent fermentation of monomers varies
    widely. Some of the factors that influence the rate of digestion
    include the nature of the fibre, the food in which it occurs, and the
    presence of substances such as phytates, lectins, tannins, and
    saponins, which appear to reduce fibre digestion (Jenkins  et al.,
    1986). The rat is considered to be a good experimental model for man
    with regard to the fermentative breakdown and bulking capacity of
    polysaccharide gums (Nyman  et al., 1986). Direct evidence for the
    degradation of polysaccharide gums in the intestine of humans was
    provided by the studies of Vercellotti  et al. (1978).

         Potential fermentation of konjac flour by human faecal flora was
    tested  in vitro with a dilute suspension of bacteria prepared from
    pooled human faeces. Konjac flour FW-KON (Lot no. 1294026; 83.4%
    soluble polysaccharide gum) and control compounds were incubated with
    faecal suspensions prepared from pooled samples provided by two
    men and two women. The control compounds tested were D-glucose,
    D-galactose, L-glucose, soluble starch, food-grade guar gum,
    food-grade xanthan gum, food-grade sodium alginate, food-grade
    carboxymethylcellulose, and food-grade pectin. Inoculated broths were
    incubated for 0, 24, 48, and 96 h under anaerobic conditions at 37C.
    At the end of the incubation period, acid production was analysed with
    a pH meter, and gas production was assessed by fluid displacement.

         There was minimal fermentation of all compounds, none inducing a
    decrease of one pH unit greater than the decrease observed in the
    basal media. Statistical differences were, however, observed between
    groups of compounds, although the data were not consistent. At 24 h,
    the pH observed with D-glucose, D-galactose, soluble starch, pectin,
    and guar gum was significantly lower than that with the basal medium.
    At 48 h, significant differences were also seen with konjac flour and
    xanthan gum, while with L-glucose, carboxymethylcellulose, and sodium
    alginate the pH remained unchanged. At 96 h, the pH changes with
    L-glucose, konjac flour, and carboxymethylcellulose were not
    significant. Significantly elevated gas production was found at 24 h
    in tubes containing D-galactose, soluble starch, konjac flour,
    or guar gum. At 48 h, increased production was also seen with
    D-glucose and pectin. At 96 h, all compounds except L-glucose,
    carboxymethylcellulose, and sodium alginate produced significantly
    more gas than the basal medium.

         The level of fermentation of konjac flour appeared to be less
    than that of D-glucose, D-galactose, soluble starch, pectin,
    and guar gum but greater than that of xanthan gum, L-glucose,
    carboxymethylcellulose, and sodium alginate (Carman  et al., 1995).

    2.1.3  Human studies

         There have been no recent studies on the digestibility of konjac
    flour in humans. Two older studies are reported below.

         In a study to investigate the digestibility of konjac flour in
    humans, one subject (the author) ate three pieces of  konnyaku
    containing about 20 g of glucomannan in his daily diet. The extent of
    digestion was ascertained on the basis of the amount of sugar-
    convertible carbohydrates excreted in the urine during consumption of
    diets with and without konjac. The author reported that about 95% of
    the konjac was digested, although how this occurred could not be
    determined (Maeda, 1911).

         In a second study, one subject ingested 30 g of  konnyaku in the
    form of a paste, with carmine as a non-absorbable marker. Faeces
    collected during the two days after ingestion and those collected in a
    subsequent two-day control period were analysed by hydrolysis with
    hydrochloric acid and analysis for glucose. The unabsorbed
    carbohydrate level was calculated from the difference in glucose
    content between the two periods. The small difference in faecal
    glucose content between the test and control periods led to the
    conclusion that 99.5% of the ingested glucomannan had been fermented
    in the large intestine. The fate of the digested  konnyaku was not
    established (Inoue, 1942).

    2.1.4  Metabolism of fermentation end-products

         The exact nature of the fermentation products of konjac flour has
    not been identified. It is, however, reasonable to assume that
    volatile (short-chain) fatty acids are the principal end-products of
    microbial degradation, as for other indigestible polysaccharides (Yang
     et al., 1970; Adiotomre  et al., 1990). Some direct evidence that
    volatile fatty acids are formed was provided in a study in rats fed
    diets containing a sweetener, fructooligosaccharide, and in which
    glucomannan was used for comparison. Both of these soluble,
    indigestible polysaccharides resulted in increased faecal excretion of
    acetate, propionate, butyrate, and isovalerate (Tokunaga  et al.,
    1986). There is ample evidence for the rapid, almost complete
    absorption of short-chain fatty acids from the colon of humans (Dawson
     et al., 1964; McNeil  et al., 1978; Ruppin  et al., 1980; Cummings
     et al., 1987), rats (Remesy & Demigne, 1976), pigs (Argenzio &
    Southworth, 1974), and dogs (Herschel  et al., 1981).

         Short-chain fatty acids (acetate, propionate, and butyrate) are
    metabolized efficiently in humans. The concentrations were decreased
    in portal, hepatic, and peripheral blood, and analysis of their molar
    concentrations indicated greater uptake of butyrate by the colonic
    epithelium and greater uptake of propionate by the liver (Vernay,
    1987; Cummings  et al., 1987). In a study in rats, the gut flora were
    found to be the main source of acetate in the blood of normally fed
    animals (Buckley & Williamson, 1977).

    2.2  Toxicological studies

    2.2.1  Short-term toxicity

         In a study to investigate the digestion and absorption of
    protein, groups of four male Sprague-Dawley rats were fed either 5%
    cellulose (control), 10% cellulose, 10% pectin, or 10% konjac for 28
    days. Body weights were recorded throughout the study, and urine and
    faeces were collected. At the end of treatment, the rats were fasted
    for 24 h and then fed 5 g/kg bw of brown rice and killed 5 h later.
    The digestive system was segmented into stomach, upper and lower

    portions of the small intestine, and large intestine, and the contents
    of each were measured. The percent protein digested by each group was
    assessed by measuring the nitrogen at intake and the levels in urine
    and faeces.

         Less protein was digested by rats fed konjac and pectin than
    those fed cellulose, and the dry weight of the faeces of the pectin-
    and konjac-fed rats was significantly lower than that of the
    cellulose-fed rats. The weights of the contents of the different
    segments of the digestive tract and the nitrogen contents of the
    stomach and upper small intestine were similar in all groups, but the
    nitrogen content of the large intestine was significantly greater in
    rats fed pectin or konjac than in those fed cellulose. Konjac at a
    dietary level of 10% thus decreased the digestion and absorption of
    protein in the large intestine, with a consequent reduction in
    body-weight gain. The study provides no indication of toxicity
    resulting from intake of konjac (Miyoshi  et al., 1987).

         In a study to investigate the hypocholesterolaemic effects of
    refined konjac meal containing about 80% glucomannan, groups of 12
    five-week-old Sprague-Dawley rats of each sex were fed either a normal
    basal diet, a hypercholesterolaemic diet (control diet containing 1%
    cholesterol), or one of three test diets containing 2.5, 5, or 10%
    refined konjac meal. Body weights were measured weekly. Four animals
    of each sex from each group were killed after 4, 8, and 12 weeks of
    treatment. Faeces were collected from all animals for three days
    before sacrifice and were dried and weighed. Total cholesterol,
    triglycerides, and high-density lipoprotein cholesterol were
    determined in sera, and total cholesterol was measured in liver. The
    iron, calcium, zinc, and copper contents of sera, femurs, and faeces
    were also determined. Livers were obtained after sacrifice, and
    sections were examined by light microscopy.

         Body-weight gain was slightly but statisticaly significantly
    lower in males fed 10% refined konjac meal than in the other groups
    during the first eight weeks, probably due to the reduced food intake
    in this group. Some rats in this group also had diarrhoea during this
    period. Similar effects were not seen in the female rats. Dry faecal
    weight was significantly greater for rats fed refined konjac meal than
    for the other groups, demonstrating the ability of refined konjac meal
    to increase stool bulk.

         Serum cholesterol levels began to decrease after four weeks in
    rats fed refined konjac meal at all doses, in comparison with the rats
    receiving high cholesterol, but had returned to normal after 12 weeks.
    The total cholesterol levels in the liver were significantly lower in
    rats fed 10% refined konjac meal than in those fed 1% cholesterol at
    four weeks. At 12 weeks, however, all treated groups showed reduced
    total cholesterol in the liver in comparison with the high-cholesterol
    control group.

         Histological examination of the livers of rats fed 1% cholesterol
    showed spreading fatty degeneration with focal necrosis and a non-
    specific inflammation reaction. Similar changes were seen in the group
    receiving refined konjac meal at the end of four weeks, but the
    changes disappeared gradually with longer feeding times, and the
    morphology of the liver was similar to that in the normal control
    group at the end of 12 weeks. Changes were also observed on gross
    examination of the liver. The authors suggested that the konjac flour
    polysaccharide binds bile acids and depresses re-absorption in the
    intestine, with a consequent reduction of lipid accumulation in the
    liver. No differences in the mineral content of the sera or femurs
    were seen between the groups at any time (Hou  et al., 1990).

    2.2.2  Long-term toxicity

         In a study designed to investigate the effects of refined konjac
    meal on calcium and phosphorus metabolism and on histopathology,
    groups of 15 Sprague-Dawley rats of each sex were fed basal diet or
    basal diet in which 1% of the cornstarch was replaced with refined
    konjac flour, for 18 months. Body weights were measured weekly for
    three months and monthly thereafter. At the end of treatment, the
    animals were killed by bleeding from the femoral artery. Brain, liver,
    aorta, kidney, spleen, and heart were removed and weighed and, in some
    cases, examined by light and electron microscopy. The left femurs were
    isolated and weighed, both fresh and dried, and the calcium and
    phosphorus contents of the serum and femurs were determined.
    Osteometry of the epiphyseal end of the left proximal tibia was also
    perfomed, involving measurement of the trabecular volume, the mean
    trabecular perimeter, the mean osteoid perimeter, the osteoid surface,
    and cortical thickness. Blood samples were taken at three and nine
    months to measure serum cholesterol.

         Body-weight gain was similar in the two groups throughout the
    study, and there was no difference in absolute or relative organ
    weights or serum phosphorus and calcium levels between the control and
    treated groups. The fresh and dried femur weights were similar in the
    two groups, although there was a significant difference between the
    sexes within each group. None of the osteometric parameters differed
    significantly with treatment. Treated male rats had a statistically
    significantly lower level of total cholesterol at nine and 18months
    and a statistically significantly lower level of triglyceride at three
    and nine but not at 18 months. Treated and control females had similar
    total cholesterol levels, but triglyceride levels were lower in the
    treated group at 18months. Electron microscopic examination of the
    liver showed smaller, more lightly stained nuclei and reduced
    bile-duct proliferation in the portal area in the treated rats. The
    endothelial cells in the aorta of treated animals were smaller and
    there was less thickening of the aortic wall. The authors concluded
    that these changes were related to less senescence in the treated than
    in the control group. There was no evidence of treatment-related
    pathological changes.

         The results thus indicate no significant effect of 1% refined
    konjac meal on calcium or phosphorus metabolism or on bone structure;
    however, treated animals had a lower level of blood lipids and fewer
    signs of senescence in the cells of the brain, aorta, liver, and
    heart. There was no evidence of toxicity. The NOAEL was 1% konjac
    meal, equivalent to an intake of 500 mg/kg bw per day (Peng  et al.,
    1994, 1995; Zhang  et al., 1994, 1995).

    2.2.3  Genotoxicity

         Konjac flour was tested for its ability to induce forward
    mutations at the thymidine kinase  (tk) locus in L5178Y tk+/-
    lymphoma cells with and without microsomal activation (S9). As konjac
    flour formed a cloudy suspension in dimethyl sulfoxide, this was
    chosen as the vehicle; the flour was found to be insoluble at
    concentrations of 125-1000 g/ml. It was not cytotoxic in a 4-h assay
    in the presence or absence of rat liver S9. Konjac flour did not
    increase the mutation frequency in the presence or absence of S9
    activation at concentrations of 7.81-1000 g/ml or 15.6-997 g/ml
    (Cifone & Bowers, 1995)

         Konjac flour was tested for its ability to induce micronuclei in
    bone-marrow cells of groups of five CD-1 (ICR) mice of each sex, which
    were given konjac flour suspended in corn oil by gavage at a dose of
    5000 mg/kg bw and sacrificed 24, 48, or 96 h later. A second group of
    mice were given deionized water and used as vehicle controls and, and
    a third group given cyclophosphamide at 80 mg/kg bw were used as
    positive controls and were sacrificed 24 h after treatment. The
    numbers of micronuclei were recorded in polychromatic erythrocytes
    from all animals; no increase in micronucleus formation was seen in
    animals given konjac flour, but the positive controls had a
    significant increase (Murli & Arriaga, 1995).

    2.2.4  Special studies: Nutrient absorption

         In a study to examine the hypocholesterolaemic effect of a series
    of polysaccharide gums, groups of five male Wistar rats were fed diets
    containing 5% of various gums, one of which was  konnyaku powder
    (konjac flour), and supplemented with cholesterol. Plasma and liver
    cholesterol levels were examined after eight days and were found to be
    significantly lowered in animals fed konjac flour (Kiriyama  et al.,
    1969). In a supplementary study, the hypocholesterolaemic activity of
    konjac flour was shown to depend to some extent on its physical
    characteristics, requiring that it be macromolecular and water-soluble
    (Kiriyama  et al., 1970).

         A review of the in-vitro studies of Kiriyama and coworkers (1974)
    (Annex 1, reference 108) suggested that konjac flour does not bind,
    sequester, or adsorb bile acids since the equilibrium of bile acids
    across a cellophane membrane in a single dialysis experiment was not
    altered by the presence of konjac flour on one side of the membrane.

    The results of another part of the study, on the effect of konjac
    flour on bile-acid transport in everted sacs from rat ileum, confirmed
    that rat ileum actively transports cholic and taurocholic acids and
    showed that this transport is significantly inhibited by the presence
    of 0.25%, but not by 0.05%, konjac flour in the outside medium. As
    binding of konjac flour to the surface of the ileal sacs appeared to
    be reversible, the inhibitory effect may be due to interference with
    micelle formation by bile acids. The study provided some evidence that
    there is a minimal inhibitory concentration of konjac flour in the
    gastrointestinal medium. In the same experiment, when pectin was used
    in the place of konjac flour, bile-acid transport was not inhibited at
    concentrations of 0.05 or 0.5%, probably because of the lower
    viscosity and water-holding capacity of pectin (Kiriyama  et al., 

         The interaction of bile acids with guar gum, konjac mannan, and
    chitosan was compared in groups of male Wistar rats fed a meal
    containing 5% of one of these polysaccharide gums; a control group was
    fed a diet containing 5% cellulose (which is considered not to bind
    bile acids or phospholipids  in vivo). The animals were killed after
    2 h, and the bile-acid content of the aqueous phase of the small
    intestine was compared with the total content. The ratios were
    considerably higher in animals fed guar gum or konjac mannan,
    indicating binding by these fibres in the intestine, probably owing to
    their very high viscosity at this concentration (Ebihara & Schneeman,

         Pectin inhibited vitamin E absorption in rats during eight weeks'
    feeding at levels of 6 and 8%, but not 3%, in the diet, again
    suggesting a minimal inhibitory concentration (Schaus  et al., 1985).

         The results of these studies provide some evidence that konjac
    flour can inhibit the transport of bile acids and absorption of
    cholesterol at relatively high doses but not at lower doses.

    2.3  Observations in humans

    2.3.1  Vitamin absorption

         The results of a study conducted by Doi and coworkers (1983) on
    normal and diabetic subjects, reviewed previously (Annex 1, reference
    108), suggested that viscous forms of polysaccharide gums, such as
    konjac flour, may form a barrier around some fat-insoluble substances
    (including glucose, essential electrolytes and cations, and possibly
    vitamin B12), therefore delaying their absorption rather than
    causing malabsorption. Because consumption of konjac flour may
    interfere with the absorption of bile acids, however, the absorption
    of the fat-soluble vitamin E, which depends on the presence of
    conjugated bile acids, may also be impaired (Annex 1, reference 108).
    The study of Doi  et al. (1983) has a number of deficiencies, the

    major one being that, although vitamin E and B12 levels were
    measured up to 24 h after consumption of meals with and without 3.9 g
    konjac flour, the serum vitamin E levelshad not returned to baseline
    by this time, and thus the measurements were stopped too soon. The
    possibility of delayed absorption rather than malabsorption of vitamin
    E cannot be discounted on the basis of these data. As the serum levels
    of bile acids were not measured in this experiment, a direct
    correlation cannot be made between interference with bile-acid
    absorption and reduced vitamin E absorption. The concentration of
    konjac flour in the gastrointestinal tract during this experiment is
    estimated to have been about 1%, on the basis of an intake of 400 g of
    food during an average Japanese breakfast (Ito, 1988). The positive
    results seen at this dose are consistent with a minimal inhibitory

         In a related study, the gel-forming gums pectin and guar gum were
    shown to reduce the rate but not the overall level of absorption of
    glucose and paracetamol, as measured by direct blood analysis in
    healthy volunteers. The gums reduced peak absorption levels but
    lengthened absorption (Holt  et al., 1979).

         The effect of konjac flour on the absorption of vitamin D was
    measured in a double-blind trial on the efficacy of konjac flour
    (identified as glucomannan) in the treatment of paediatric obesity.
    The study involved 60 children under the age of 15 (mean age, 11.2
    years; mean overweight, 46%). Thirty children received 1 g of
    glucomannan twice daily for two months, and the other 30 children
    received a placebo on the same schedule. The children received a
    normal level of calories and were evaluated every two weeks for weight
    changes in comparison with their initial weights. Clinical side-
    effects were evaluated in both groups by measuring 25 indicators of
    intestinal absorption, lipid metabolism, and thyroid and adenocortical
    function, and the presence of clinical symptoms such as constipation,
    diarrhoea, and abdominal pain. One of the parameters used to examine
    intestinal absorption was serum vitamin D levels, which were measured
    at the beginning and end of the study.

         The two groups lost similar amounts of weight during the
    two-month period, but the authors suggested that the decrease in
    weight was due to continuous supervision. No significant differences
    were found in intestinal absorption, thyroid or adenocortical
    function, or clinical symptoms; however, significant differences were
    found in lipid metabolism, the treated group having decreased
    a-lipoprotein and increased pre-b-lipoprotein and triglyceride. Serum
    vitamin D levels were similar in the two groups at the beginning and
    end of the study (Vido  et al., 1993).

    2.3.2  Cholesterol absorption

         In order to obtain a better understanding of the results of the
    studies on vitamin absorption, the general properties of
    polysaccharide gums, and specifically konjac flour, have been
    considered. Two important properties of polysaccharide gums are their
    ability to slow gastric emptying (Schwartz  et al., 1982; Vahouny &
    Cassidy, 1985) and to alter gastrointestinal transit times (Gohl &
    Gohl, 1977; Schneeman, 1994). These characteristics are considered to
    be related to the viscosity and water-holding capacity of these gums
    (Eastwood  et al., 1983; McBurney  et al., 1985). Polysaccharide
    gums influence the absorption of fat-soluble substances in two ways.
    Firstly, they may cause an increase in the so-called 'unstirred layer'
    or diffusion barrier on the mucosal surface (Vahouny & Cassidy, 1985;
    Schneeman, 1994). Changes in the viscosity of this layer change its
    apparent thickness (Anderson  et al., 1989), and, because this layer
    is rate-limiting in absorption, absorption rates from the intestine
    are slowed and absorption along a greater length of the gut is
    promoted (Schneeman, 1994). Secondly, polysaccharide gums may reduce
    the level of enterohepatic circulation of bile acids and thus
    interfere with bile-acid emulsification of fatty substances
    (Vahouny & Cassidy, 1985). Whatever the mechanism, dietary intake of
    polysaccharide gums, including konjac flour, lowers the serum levels
    of fat-soluble substances such as cholesterol. Thus, studies on the
    effect of konjac flour on serum cholesterol may be indicative of
    effects on other fat-soluble substances such as vitamins.

         The results of a clinical study by Zhang and coworkers (1990),
    designed to examine the effect of daily consumption of foods
    containing 5 g konjac flour on lipid metabolism, were reviewed
    previously (Annex 1, reference 108). At the end of the 44 days of
    treatment, total serum cholesterol, triglycerides, and low-density
    lipoprotein levels were significantly reduced and that of high-density
    lipoprotein was significantly increased in the treated group as
    compared with the controls. After the 45-day recovery period, however,
    there were no differences in these parameters between the groups.

         The results of a clinical study by Huang  et al. (1990), which
    was designed principally to examine the effects of konjac flour on
    blood glucose levels in 72 diabetic patients over a 65-day period,
    were also reviewed previously (Annex 1, reference 108). Overall, the
    study did not indicate that 2% konjac flour in the diet lowers blood
    lipid levels, except in 13 subjects with hyper-triglyceridaemia in
    whom triglyceride levels were significantly decreased.

         The results of these two studies suggest that the effect of
    konjac flour on blood cholesterol levels is dose-dependent and perhaps


         The Committee reviewed data from additional short-term studies
    and a long-term toxicity study, all conducted in rats. The short-term
    studies were a 28-day study on the effect of konjac flour on
    protein digestion and absorption and a 12-week study on the
    hypocholesterolaemic effect of konjac flour. The additional long-term
    study in rats addressed the effect of konjac flour on calcium and
    phosphorus metabolism and histopathology. While these studies were not
    specifically designed to assess the potential toxicity of konjac
    flour, no evidence of toxicity was reported with 10% in the diet for
    up to 12 weeks or with 1% in the diet for 18 months. Two additional
    studies on genotoxicity provided no evidence of potential to induce
    forward mutations at the thymidine kinase locus in cells in culture or
    to induce micronuclei in mouse bone marrow. The Committee also
    considered some additional data on the fate of konjac flour in the
    large intestine, including a recent study of human faecal flora
     in vitro, which showed that extensive hydrolysis of konjac flour
    occurs in the large intestine. Konjac flour underwent less
    fermentation than D-glucose, D-galactose, soluble starch, pectin, and
    guar gum but more than xanthan gum, L-glucose, carboxymethyl-
    cellulose, and sodium alginate. Although only indirect evidence was
    provided, the Committee concluded that konjac flour, like other
    polysaccharide gums, undergoes fermentation in the large intestine to
    fatty acids (acetate, propionate, and butyrate).

         The Committee reviewed data from studies in animals and humans
    on the effect of konjac flour and other polysaccharide gums on the
    absorption of fat-soluble vitamins and cholesterol and the
    re-absorption of bile acids. The available data indicate that konjac
    flour affects the absorption of vitamin E and cholesterol only at high
    doses (possibly through interference with bile-acid micelle formation
    and subsequent interference with transport mechanisms). The Committee
    noted that there were still no definitive studies to establish the
    threshold dose of konjac flour that affects vitamin E absorption but
    considered that it was likely to be much higher than the levels of
    intake of konjac flour when used as a food additive.


         The Committee stressed that its evaluation applies only to the
    use of konjac flour as a food additive. The Committee concluded that
    the additional studies provided no evidence of adverse effects
    attributable to konjac flour in experimental animals. Metabolically,
    konjac flour behaves in the intestine in a similar way to other
    polysaccharide gums. On the basis of this re-assessment and on the
    anticipated levels of use as a food additive (as a thickener,
    emulsifier, stabilizer, gelling agent, texturizer, and glazing agent),
    the Committee established an ADI 'not specified' for konjac flour.


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    See Also:
       Toxicological Abbreviations
       Konjac flour (WHO Food Additives Series 32)
       KONJAC FLOUR (JECFA Evaluation)