it is predicted that by 2015 approximately 2.3  billion adults will become overweight , and more than 700  million will be obese . dyslipidaemia is a pathological disorder , and current evidence has highlighted not only total cholesterol but also triacylglycerol ( tag ) as lipid risk factors in metabolic syndrome . recently , community awareness in nutrition as a cornerstone for healthy life style has increased . functional food is a concept of nutrition , based on the role of reducing the risk of disease . a food will be considered   as a functional food if it gives one or more benefits or positive effects to the body beyond adequate nutritional effects in a way that is relevant to either improve the stage of health and well - being and/or reduce the risk of disease . shiitake mushrooms are the second most popular and the third widely cultivated edible mushroom in the world . certain components of shiitake mushroom have hypolipidaemic effect , such as eritadenine and -glucan .   although it has been reported that eritadenine extracted from shiitake mushroom has hypolipidaemic effect , most of these studies emphasize on the mechanism in hypocholesterolaemic effect [ 58 ] but not the effect on triglyceride . also present at high levels in graminaceous crops such as barley , rye , and oat and also in bacteria , fungi , and edible mushrooms , but the structure can vary from source to source . studies have reported that oat -glucan can increase satiety , reduce food intake , delay nutrition absorption , and reduce plasma lipid levels [ 1012 ] . although mushroom has been shown to improve lipid profiles [ 1315 ] , studies in this regard are incomplete . some studies have reported single - dose effect on obesity - associated metabolic disorders using mushroom powder supplementation [ 13 , 1618 ] . however , no data are currently available on the ability of shiitake mushroom to affect food intake , body fat deposition , and plasma triglyceride concentrations in a dose response manner .   studies have shown that high - fat diet - induced obesity in rodents can develop dyslipidaemia , insulin resistance , and altered metabolic regulatory hormones [ 1922 ] . the diet - induced obese animal model mimics human obesity more than other models such as genetic knockout mutants . this study has systematically examined the effects of shiitake mushroom on plasma lipid profiles , various types of fat depositions , energy efficiency , and body fat index as well as their relationships in a dose - response manner in rats fed a high - fat diet . all experimental procedures were approved by the animal ethics committee of the university of wollongong , ae 09/01 . forty wistar rats , at 9 weeks of age , were obtained from animal resource centre ( arc)-perth , western australia , and were given one week acclimatization to their new environment . they were housed two per cage in environmentally controlled conditions ( temperature 22c , light cycle from 06:00 to 18:00 hours , and dark cycle from 18:00 to 06:00 hours ) and had ad libitum access to food and water . all rats were fed standard laboratory nonpurified diet ( ys feeds pty - ltd , young , nsw , australia ) during the acclimatization period . the forty rats were divided into four groups ( n = 10 ) and fed 50% high - fat diets with an addition of nil , low , medium , or high - dose of shiitake mushroom powder ( hfd , 7  g / kg ld - m , 20  g / kg md - m , or 60  g / kg hd - m , resp . ) . the food was produced from semisynthetic material according to the recommendation of american institute of nutrition ain-93 for rodent . hfd consisted of the following ( g / kg ) : corn starch , 210 ( goodman fielder , nsw , australia ) ; sucrose , 175 ( bella - vista , nsw , australia ) ; copha , 105 ( peerless food , victoria , australia ) ; lard , 105 ( fonterra brand , victoria , australia ) ; sunflower oil , 50 ( goodman fielder , nsw , australia ) ;   gelatine , 50 ( sunny hills , qld , australia ) ; casein , 128 ( fonterra ltd , auckland , new zealand ) ; fiber , 51 ( nature , rosenberg , germany ) ; mineral , 67 ( mp biomedical , ohio , usa ) ;   vitamin , 13 ( mp biomedical , ohio , usa ) . this study used shiitake mushroom powder containing 30%  -glucan ( w / w ) analysed with a megazyme -glucan kit . food intake was measured every 24  hours by weighing the amount of total food ( g ) provided to the rats and subtracting the remaining food ( g ) in the cage after 24  hours . following the intervention period , rats were killed via carbon dioxide asphyxiation . the white adipose tissue ( wat ) comprised of visceral fat ( epididymal , perirenal , and omental fat ) and subcutaneous fat ( inguinal fat ) and brown adipose tissue ( bat ) was calculated as the total amount of epididymal , perirenal , omental , and inguinal fat deposits per 100  g body weight . the energy efficiency ratio ( eer ) was calculated by body weight gain ( bwg ) per the amount of energy intake ( g / kj ) . blood samples were obtained by puncturing the right ventricle of heart after euthanasia and were collected in ethylenediaminetetraacetic - acid- ( edta- ) coated tubes and centrifuged at 3000  rpm at 22c for 25  minutes . high - density lipoprotein ( hdl ) was isolated from plasma with dextran sulphate and magnesium chloride , based on a modified method from sjoblom and eklund . total plasma cholesterol ( tc ) , tag and hdl cholesterol were measured using the konelab 20xt with infinity reagent from thermo fisher scientific ( auburn nsw , australia ) . food intake , bwg , eer , bfi , adipose tissue , and plasma lipids were presented as mean and standard errors . statistical analysis was performed using spss software ( version 17.0 , spss inc , chicago , ill , usa ) . one - way anovas were used , followed by a post hoc tukey - kramer significant differences test for multiple comparisons among the groups . no differences in the amount of food or energy intake were found among all groups ( table 2 ) . this study found significant effects of dietary intervention on body weight gain ( f3,38 = 6.204 , p = 0.002 , table 2 ) . rats on a high dose of shiitake mushroom diet ( hd - m group ) had 35% and 39% lower body weight gains than rats on low- and medium - shiitake mushroom diets , respectively ( p < 0.05 ) . there was also a trend of lower body weight gain in the hd - m group compared with the hfd group ( 23% , p = 0.077 ) . overall , there were significant effects in total fat masses due to dietary interventions ( f3,38 = 4.355 , p = 0.010 , table 2 ) . rats on hd - m diet had significantly lower total fat masses , 35% and 37% , than the hfd and ld - m groups , respectively . furthermore , hd - m group also had a trend of lower fat accumulation than the md - m group ( 32% , p = 0.076 , figure 1 ) . the white adipose tissue in md - m group was 35% and 37% lower than the hfd and ld - m groups , respectively ( f3,38 = 4.340 , both p < 0.05 ) . the visceral fat mass ( epididymal + perirenal + omental ) was the lowest in the hd - m group among all groups ( f3,38 = 4.215 , p = 0.012 , table 2 ) . furthermore , hd - m group had significantly lower perirenal ( 39% ) and inguinal fat ( 52% ) compared to hfd group . epididymal and omental fat masses were 29% and 21% lower in the hd - m group than hfd group ( p = 0,05 ) . the bfi was significantly different between four diet groups ( f3,38 = 5.86 ; p = 0.002 ) . results showed that rats on a hd - m diet had a significantly lower bfi than the rats on hfd , ld - m , and md - m diets ( 35% , 33% , and 30% , resp . ) . no differences were found in the bfi between the hfd , ld - m , and md - m groups ( figure 2 ) . there was a significant difference in eer among four diet groups ( f = 5.425 , p = 0.004 , figure 3 ) . the hd - m group had a significantly lower eer than the ld - m and md - m groups ( 30% and 34% , resp . ) but was not significantly different from hfd . furthermore , there were no statistical differences in eer between the hfd , ld - m , and md - m groups . there was a significant difference in plasma tag levels between the four groups ( f3,38 = 7.445 ; p = 0.001 ) . the rats on the hd - m diet had significantly lower levels of tag than hfd , ld - m , and md - m ( 55% , 41% , and 46% , resp . ) . there were no significant differences among the hfd , ld - m , and md - m groups ( figure 4 ) . plasma total cholesterol levels did not differ between four groups ( p = 0.125 ) . although rats on an hd - m diet had the highest level of plasma hdl , no statistical difference was found ( hd - m : hfd : ld - m : md - m   = 1.26  0.01 : 1.12  0.02 : 0.95  0.02 : 0.84  0.01 this study found that the amount of shiitake mushroom added in a high - fat diet ( 50% fat in kcal ) was negatively associated with the bwg , wat , tag , bfi , and eer ( figure 5 ) . no statistical difference was found between the amount of shiitake mushroom diets and plasma cholesterol and hdl concentrations ( data not shown ) . this study showed that adding hd - m in a high - energy diet containing 50% fat can significantly prevent total fat deposition and significantly lower plasma tag in rats compared with no addition of shiitake mushroom diet . it was also found that plasma tag - lowering effect was negatively associated with the amount of shiitake mushroom supplementations and positively associated with the amount of visceral fat . studies have been carried out to test plasma tag - lowering effect by adding mushroom powder into the diets . the results varied , where studies showed a significant effect of lowering plasma tag [ 14 , 15 , 18 , 28 , 29 ] , whilst other did not [ 17 , 30 , 31 ] . the first is related to the amount of sucrose in the diet which can lead to a high level of plasma tag in rodents [ 17 , 18 ] . high - sucrose diet promotes a hyper - tag plasma level by increasing hepatic tag secretion and decreasing tag removal . a previous study has reported that if the sucrose amount in the diet is greater than 40% from total energy , the increasing of plasma tag is difficult to prevent by enriched mushroom powder diet .   in this study , the    high - fat diet group as controls supplied 15% sucrose from total energy . studies have shown that adding less than 5% ( wt  :  wt ) mushroom powder in the diet does not significantly decrease plasma tag , irrespective the sources [ 13 , 14 , 17 , 18 , 30 , 31 , 33 ] , which is also what we have found . therefore , the ratio between the amount of sucrose and enriched mushroom in the diet is important for plasma tag - lowering effect . the duration of the dietary intervention using mushroom powder seems less important as it is compared with the dose . some short - term studies , 3 to 5 weeks [ 18 , 33 ] , reported a reduction of plasma tag concentration , whilst others [ 1618 ] reported no effects . likewise , the longer - intervention studies , such as 6- to 10-week interventions , also showed mixed results with some having no effect   and others with positive outcomes to prevent increasing plasma tag levels [ 15 , 30 ] . hence , the dose of mushroom powder is more important than duration of supplementation . it is largely unreported to use fat masses as an indicator to determine the effect of adding mushroom to a diet on body weight gain .   in animal studies , there are currently limited data relating to the analysis of body fat masses . kabir and kimura   reported that giving 5% shiitake mushroom and 5% maitake mushroom for 8  weeks to spontaneous hypertensive rats ( hsrs ) did not significantly lower adipose tissue compared to control group . there is also a lack of study to define the effect of mushrooms on total fat masses in the human study . in this study , we have demonstrated that the high - dose shiitake mushroom lowered total fat deposition . in addition , there was a negative correlation between an increased dosage of shiitake mushroom and a lower body fat index . previous study reported that reducing of plasma tag is associated with the decrease of total fat masses as white adipose tissue , which is consistent with our results . weight - loss interventions are commonly prescribed for obesity to reduce risk factors associated with metabolic disease . studies from animal experiments showed various results in terms of adding mushroom powder in diets affecting body weight gain and obesity . for example , a study   showed a decrease in body weight gain by 53% by adding 2% extracts of agaricus blazei mushroom in the diet for 6  weeks in diabetes mellitus sprague - dawley rats induced by streptozotocin . again , body weight gain was significantly reduced by 25% when adding 20% maitake mushroom powder to a hypercholesterolemic diet for 25 weeks . however , no statistical difference in body weight changes was reported in apoe mice after being given a diet containing 3% bunashimeji mushroom powder for 10  wks . a similar result also reported that additional 5% mushroom powder in the diet for four or eight weeks had no effect on lowering body weight gain in spontaneous hypertension rats or male f344/ducrj rats [ 17 , 30 ] . it appears that different species of animal respond differently in body weight gain to the dietary intervention using mushroom powder . the dosages less than 5% mushroom powder seem to be less likely to give any favourable effect to prevent body weight gain . the initial body weight and age of animal model seem to have no affect on the outcome of mushroom treatment to prevent the increase of body weight [ 1618 , 30 ] . this study showed that body weight gain was significantly lower in the hd - m group than the md - m and ld - m groups . this suggests that there was a threshold effect in terms of the amount of shiitake mushroom intake for the prevention of weight gain in rats on a high - fat diet . as an estimate of hd - m diet in rats , 90  g mushroom powder per day may be required for humans to prevent body weight gain and lower tag . however , this must be tested in humans before the recommendation is given . on the other hand , a low - dose mushroom diet may not be strong enough to prevent weight gain . for example , studies have shown that supplementation of the diet with 30  g maitake mushroom per day for 21 days did not achieve body weight lowering effect in patients with moderate dyslipidaemia . this study found a diet of hd - m significantly lowered the energy efficiency ratio ( eer ) compared to ld - m and md - m diets . this is in agreement with a previous study showing that high - dose shiitake mushroom diet lowers energy efficiency in rats on a high - fat diet as adding maitake mushroom ( 20% ) into hypercholesterolemic diet for 4 weeks reduces 27% energy efficiency in body weight gain in rats . the exact mechanism is not clear how shiitake mushroom diet resulting in lowering body weight gain , fat masses and plasma tag . , -glucan may enhance luminal viscosity , delay gastric emptying , and/or reduce intestinal absorption . secondly , shiitake mushroom could reduce nonesterified fatty acid ( nefa ) derived from tag as a source of adipose tissue . lipolysis of chylomicron and vldl - tag are major determinants of adipose tissue development , and the reduced wat may be affected by the low - nefa source that enters to adipose tissue .   a low nefa in adipose tissue is possibly affected by the activity of enzyme lpl as main gate keeper entry into adipose tissue . the overexpression of lpl in muscle prevents hfd - induced lipid accumulation in adipose tissue . increased lpl in skeletal muscle leads to an enhanced tag storage in muscle and then diverts lipoprotein tag - derived nefa away from storage in adipose tissue to oxidation in the muscle . thirdly , the possibility that eritadenine from shiitake mushroom could inhibit the release of triacylglycerol from the liver . the eritadenine has been reported to inhibit the production of phosphatidylcholine that influences the release of vldl and hdl from liver . studies showed that adding eritadenine extracted from shiitake mushroom in the diet can decrease plasma tag by 27% in a cholesterol diet , 20% in cholesterol free diet , and 2% in diet with choline chloride added [ 57 ] . the 50  mg eritadenine per kg diet was shown to be sufficient to elicit hypolipidaemic effect in rats . the hd - m diet used in this study contains ~200  mg / kg food . since tag was low in hd - m diet , it will be interesting to examine tag in various organs to ensure its possible storage or exclusion .   in view of that , fat content in faecal , plasma nefa concentration , and accumulation of tag in the liver and muscle will need to be examined to verify its potential side effects .   in conclusion , adding high shiitake mushroom in a high - fat diet can prevent body weight gain , fat deposition , and plasma tag in rats , while further study is necessary to elucidate the underlying mechanisms and the possibility component of shiitake mushroom of these important effects . this study encourages an effort pursuing human clinical trial using shiitake mushroom for prevention and treatment of obesity and its related metabolic disorders .
high - fat diet ( hfd ) induces obesity . 
 this study examined the effects of shiitake mushroom on the prevention of alterations of plasma lipid profiles , fat deposition , energy efficiency , and body fat index induced by hfd . 
 rats were given a low , medium , and high ( 7 , 20 , 60  g / kg = ld - m , md - m , hd - m ) shiitake mushroom powder in their high - fat ( 50% in kcal ) diets for 6 weeks . 
 the results showed that the rats on the hd - m diet had the lowest body weight gain compared to md - m and ld - m groups ( p < 0.05 ) . 
 the total fat deposition was significantly lower ( 35% , p < 0.05 ) in rats fed an hd - m diet than that of hfd group . 
 interestingly , plasma triacylglycerol ( tag ) level was significantly lower ( 55% , p < 0.05 ) in rats on hd - m than hfd . 
 this study also revealed the existence of negative correlations between the amount of shiitake mushroom supplementation and body weight gain , plasma tag , and total fat masses .