高直链玉米淀粉对卵巢切除大鼠体内胆固醇代谢影响的研究

目的:研究高直链玉米淀粉(HACS)对因雌性激素缺乏引起的高胆固醇血症的影响。方法:将36只Wistar成年雌鼠随机分为6组,5组进行双侧卵巢切除手术(OVX),分别喂食不添加(对照)和添加10%、20%、30%、40%HACS的饲料,另1组进行卵巢伪切除手术,喂食不添加HACS的对照饲料。实验喂养4w后解剖,测定血清和肝脏中胆固醇、甘油三酯浓度、肝脏胆固醇羟化酶(CYP7)活性以及小肠、盲肠中胆汁酸总量和粪中胆汁酸排泄量等指标。结果:OVX组大鼠血浆和肝脏中胆固醇和甘油三酯浓度显著高于伪切除组大鼠。与对照饲料组相比,饲料中添加20%和30%HACS能显著降低血清中甘油三酯浓度;添加30%和40%HACS能显著降低去势大鼠血清胆固醇;添加30%和40%HACS显著增加了小肠中胆汁酸含量和粪中胆汁酸排泄量;各组间CYP7活性没有显著性差异。结论:HACS对因雌性激素缺乏引起的高胆固醇血症有明显降低效果,可能的作用机制是通过增加肠道中胆汁酸总量和粪中胆汁酸的排泄量来降低血液中胆固醇浓度。     

富含抗性淀粉转基因大米对大鼠肠道健康的影响

目的研究富含抗性淀粉转基因大米对大鼠肠道健康的影响。方法48只健康成年雄性SD大鼠按体重随机分为4组:分别给予非转基因大米最大量掺入的饲料(No-GM组)、转基因大米最大量和半量掺入的饲料(GM组、Half-GM组)和正常对照饲料重(ND组)。喂养5w后连续收集4d粪便;6w后处死大鼠并收集盲肠、结肠内容物,测定内容物和肠壁量、pH值、短链脂肪酸(SCFA)等反映肠道健康的指标。结果GM组的体重接近ND组,显著低于No-GM组。与No-GM组和ND组相比,GM组和Half-GM组粪便量、粪便水分、盲肠壁以及内容物含量显著增加,并存在显著的量效关系(P<0.05)。GM组结肠壁质量与No-GM组和ND组也有显著差异。盲肠、结肠和粪便中SCFA的含量逐渐降低,除了Half-GM组结肠中丁酸含量与其他各组没有差异外,GM组和Half-GM组盲肠、结肠中SCFA含量与No-GM组和ND组相比都有增加,各组大鼠粪便中丁酸含量的差异消失,但是乙酸和丙酸含量仍然存在差异。GM组和Half-GM组粪便和盲肠的pH值非常显著低于No-GM组和ND组。结论抗性淀粉转基因大米能改善大鼠肠道健康。     

抗性淀粉对大鼠肠道菌群的影响

目的观察抗性淀粉(RS)及其不同类型的摄入对大鼠肠道常见菌群的影响。方法将32只大鼠按体重随机分为4组,每组8只,分别喂以不含RS的饲料、含6%二型抗性淀粉(RS2)、含12%RS2和含6%三型抗性淀粉(RS3)饲料4周。收集大鼠实验前后的粪便,检测其pH值和5种常见菌群(大肠杆菌、拟杆菌、肠球菌、双歧杆菌、乳杆菌)的分布。饲养4周后,处死大鼠取其盲肠内容物,检测其pH值和短链脂肪酸(SCFA)的含量。结果RS2和RS3均可明显增加大鼠粪便中双歧杆菌菌落数(P<005),显著减少肠球菌落数(P<005);盲肠内容物的SCFA随RS2摄入增加而增加,12%RS2组显著高于对照组(P<001),也高于6%RS2组(P<005);RS可降低大鼠盲肠内容物和粪便的pH值(P<005),降低效果随RS摄入量增加而加大,且RS3组优于RS2组(P<005)。结论抗性淀粉可明显改善机体的肠道菌群,并增加其酵解产物SCFA,降低肠道pH值,从而发挥对机体的健康作用。     

抗性淀粉对大鼠肝脏胆固醇代谢相关基因表达的影响

目的:观察抗性淀粉(RS)对大鼠肝脏胆固醇代谢相关基因表达的影响,探讨RS干预胆固醇代谢的作用机制。方法:将18只大鼠随机分为三组,分别饲食正常化学纯合饲料(对照组)、含15%RS纯合饲料(低RS组)和含30%RS纯合饲料(高RS组)6w。采用实时荧光定量PCR技术检测各组大鼠肝组织中胆固醇7a-羟化酶(CYP7A1)、肝清除细胞B1受体(SR-B1)、肝低密度脂蛋白受体(LDLR)mRNA表达水平。检测各组大鼠血胆固醇、盲肠内容物短链脂肪酸(SCFA)含量。结果:大鼠肝组织CYP7A1mRNA、SR-B1mRNA、LDLRmRNA表达水平及盲肠内SCFA含量,高RS组与对照组相比显著增加(P<0.05)。血清胆固醇水平,RS干预组显著低于对照组(P<0.05)。结论:RS通过增强肝组织胆固醇代谢相关基因表达水平,增加盲肠内SCFA含量,发挥降低血胆固醇的作用。     

花椒麻味物质对糖尿病大鼠肠道微生态的影响

目的探讨花椒麻味物质对糖尿病大鼠肠道微生态的影响。方法以腹腔注射60mg/(kg·bw)链脲佐菌素(STZ)建立糖尿病大鼠模型。将大鼠分为空白组、模型组、花椒麻味物质低、中、高[3、6、9 mg/(kg·bw)]剂量组,每组8只。连续灌胃28d后,检测大鼠盲肠组织,盲肠内容物pH值、游离氨、短链脂肪酸(SCFA)及主要肠道菌群等指标,并观察回肠病理切片。结果与空白组相比,模型组大鼠盲肠组织总重、盲肠组织表面积、pH值、游离氨的含量及其肠球菌、肠杆菌等条件致病菌的数量显著增加(P0.05),而SCFA含量、双歧杆菌、乳酸杆菌等有益菌群的数量显著降低(P0.05),说明糖尿病大鼠发生了肠道微生态紊乱。与模型组相比,花椒麻味物质可显著降低盲肠组织重量及盲肠内容物pH值、游离氨的含量(P0.05),并能抑制肠道中肠杆菌、肠球菌等条件致病菌的生长;显著增加盲肠内容物中SCFA含量及其乳酸杆菌、双歧杆菌等有益菌群的数量(P0.05),改善大鼠回肠组织形态,但高剂量组会导致大鼠回肠组织肠道黏膜及其细胞结构损伤。结论适量的花椒麻味物质对糖尿病大鼠的肠道微生态紊乱具有一定的调节作用。     

不同膳食模式及添加大豆低聚糖对肠道短链脂肪酸的影响

目的:探讨不同膳食模式及添加大豆低聚糖对肠道内短链脂肪酸(short-chain fatty acids,SCFA)的数量和种类的影响。方法:选择12名20～25岁健康在校大学生,分三阶段给予三种不同膳食及服用大豆低聚糖,每一阶段第1w食用三种实验膳食(1.低动物性食物模式LAFD,2.动植物食物平衡模式BD,3.高动物性食物模式HAFD),第2w添加大豆低聚糖,第3w恢复原实验膳食,准备下一阶段试验。试验共进行9w,每周前后收集粪便,利用毛细管柱顶空气相色谱法测定粪便中的SCFA。结果:LAFD干预后SCFA总量增加,差异有显著意义(P<0.05),且以乙酸、丁酸增加为主。BD和HAFD干预后SCFA总量没有改变。在三种干预膳食基础上添加大豆低聚糖后,LAFD时SCFA总量变化不明显,BD和HAFD时SCFA总量均有显著增加(P<0.05),且BD时以乙酸、丙酸增加为主,HAFD时以丙酸、丁酸增加为主。结论:膳食中植物性食品或动物性食品对人体肠道内SCFA的含量、种类均有影响。大豆低聚糖添加在动植物平衡膳食模式和高动物性食物膳食模式下效果更好。     

低聚果糖对大鼠结肠癌前期病变形成的影响

目的探讨低聚果糖对大鼠结肠癌前期病变-畸变隐窝病灶(ACF)形成的影响.方法48只雄性Wister大鼠经适应性喂养1周后随机分为A、B、C和D组,每组12只,B、D组大鼠每周皮下注射1次二甲基肼(20 mg/kg),A、C组大鼠给予等量生理盐水,连续10周;同时A、B组大鼠给予标准鼠食,而C、D组大鼠给予含10%低聚果糖的鼠食,喂养至第12周处死,观察大鼠体重、结肠长度和ACF,以及结肠内容物重量及其丁酸含量的变化.结果各组大鼠体重增加及结肠长度差异无显著性,腹腔内脏器未见明显病灶.C、D组盲肠内容物重量显著高于A、B组,但各组近、远端结肠内容物重量差异无显著性.C、D组各肠段内容物丁酸浓度显著高于A、B组的相应肠段,D组≥4个隐窝的ACF数均显著低于B组,且丁酸浓度和ACF总数呈显著的负相关.结论低聚果糖能抑制大鼠结肠癌前期病变的形成.     

饲粮淀粉来源对肉仔鸡淀粉消化和肠道发育的影响

目的研究饲粮淀粉源对肉仔鸡生长性能、淀粉消化性能以及肠道发育的影响。方法选取360只1日龄AA肉仔鸡健雏,随机分为3个处理组,分别饲喂3种不同淀粉来源饲粮(玉米、小麦、碎米),每个处理6个重复,饲养至28 d,分离肠道,测定各肠段长度,肠道内容物淀粉含量及饲料淀粉含量。结果不同淀粉源饲粮对试验期末肉仔鸡体重、平均日增重和采食量影响显著(P<0.05);碎米组饲粮在肉仔鸡小肠中的停留时间(152.76 min)显著高于玉米饲粮组(126.17 min)和小麦饲粮组(133.30 min)(P<0.05),淀粉消化速率低于玉米组(1.97 h-1)和小麦组(1.57h-1);碎米组十二指肠、空肠、回肠长度均低于玉米和小麦组。结论不同淀粉源饲粮引起了肉仔鸡早期生长性能,淀粉消化能力和肠道发育情况的变化。[营养学报,2012,34(4):340-343,348]     

膳食中的糖精钠对盲肠菌丛的影响

本实验用刚断乳的Charles River种雄性大鼠,分为实验组及对照组,均喂以标准饲料。实验组7只动物,饲料中含有7.5%的糖精钠;对照组5只动物,饲料中含有7.5%的纤维素。自由取食与饮水,实验期10天。实验结束时称量体重,称盲肠组织及内容物重量,并培养计算内容物中好气菌与厌气菌的菌落数目,及测定内容物的糖精含量。结果表明,喂糖精动物的粪便较软,实验期的前7天外观粘稠、不成团块,嗅味较小,异于对照组及正常大鼠粪便。体重增长比对照组约低30%。每100 g体重的盲肠组织重量比对照高45%,而盲肠内容物重量高80%。盲     

复合膳食纤维对大鼠肠道形态结构及功能的长期影响

为观察长期进食复合膳食纤维 (DFC)对高脂血症大鼠肠道形态结构及功能的影响。选健康、断乳SD大鼠 60只 ,雌雄各半 ,经高脂饲料诱导形成高脂血症模型后 ,按体重及血胆固醇水平均衡的原则分为 5组 ,分别以基础饲料及小麦纤维作为对照组 (A、B)其余 3组给不同剂量的DFC(C～E组 ,总膳食纤维含量分别为 4 %、1 6 %、64 % ) ,实验期为三月 ,通过测量分析及光镜、电镜形态观察的方法 ,研究DFC对大鼠肠道结构与功能的影响。结果显示 ,1 DFC含量较高剂量的D、E两组动物粪重显著增加 ,小肠壁重量显著高于正常及高脂对照组 ,E组动物盲肠壁重量显著高于正常及高脂对照组 (P <0 0 5) ;2 不同水平DFC组大鼠小肠绒毛变短、变宽 ,粘膜肌层增厚 ,最高剂量的E组动物小肠绒毛出现水肿 ;各水平DFC组动物直肠光镜下无明显形态学改变 ;3 各水平DFC组大鼠小肠微绒毛不同程度变短 ,排列紊乱 ,局部缺失 ,细胞器肿胀 ,以线粒体病变最为明显 :基质肿胀、嵴断裂、有的消失 ,重出现空泡变 ;4 直肠微绒毛改变不明显 ,线粒体改变同小肠。结论长期摄入高剂量DFC在增加粪便量排出的同时会影响大鼠肠道的形态结构 ,可能会对肠道的某些功能产生不利影响 ,实际应用时应以低剂量为宜     

Heat moisture treatment of high amylose cornstarch increases its resistant starch content but not its physiologic effects in rats

To examine whether the physiologic effects of high amylose cornstarch (HACS) are affected by gelatinization or heat moisture treatment, male rats were fed for 21 d a fiber-free purified diet containing 40 g/100 g gelatinized normal cornstarch (G-CS), HACS, gelatinized high amylose cornstarch (G-HACS) or heat moisture-treated HACS (HMCS). Dietary fiber (DF) content in G-HACS was 87% lower than that in HACS. The apparent starch and protein digestibilities were higher in the G-HACS group than in the HACS group. Fecal wet weight and fecal bile acid excretion were lower in the G-HACS group than in the HACS group. The cecal tissue weight, cecal surface area, cecal content weight and cecal pH were lower in the G-HACS group than in the HACS group. The cecal n-butyric acid and succinic acid concentrations were higher and lower, respectively, in the G-HACS group than in the HACS group. The plasma cholesterol and triacylglycerol concentrations did not differ between the G-HACS group and the HACS group. On the other hand, the DF content in HMCS was 330% higher than that in HACS, but the HMCS and HACS groups generally did not differ except in cecal surface area. Dietary starch did not affect fecal moisture, fecal neutral sterol (cholesterol + coprostanol) excretion, liver cholesterol level, total short-chain fatty acid (SCFA) concentration or apparent Ca, Fe, Mg and Zn absorptions. These results show that the heat moisture treatment of HACS for the most part does not alter its physiologic effects despite the greater DF content.     

The influence of dietary fiber on proliferation of intestinal mucosal cells in miniature swine may not be mediated primarily by fermentation.

Cannulated miniature pigs were used as a model for evaluating the effects of fiber-containing diets on proliferation of colonic epithelial cells. Biopsy specimens taken from the mucosa of the cecum and distal colon were incubated in [3H]thymidine and processed using autoradiography. Digesta from the cecum was analyzed for concentrations of short-chain fatty acids (SCFA), pH and volume. Cellular proliferation at both intestinal sites was influenced by the source or quantity of dietary fiber. These dietary variables also influenced SCFA concentrations and pH of cecal digesta and the volume of contents in the fermentation chamber. Cellular proliferation was not significantly correlated, however, with the quantity of water-soluble dietary fiber consumed, with SCFA concentrations or pH of the cecal digesta, or with the volume of the fermentation chamber. We suggest that the influence of dietary fiber on intestinal cell proliferation cannot be predicted from markers of the fermentation capacity of specific diets, because fiber likely influences intestinal proliferation through several interactive mechanisms, some of which include luminal factors.     

Whole wheat and triticale flours with differing viscosities stimulate cecal fermentations and lower plasma and hepatic lipids in rats

Whole flours from oat, rye or barley effectively modify digestive fermentation and lipid metabolism, whereas the effectiveness of whole wheat flour has not been established. To address this question, cecal digestion, short-chain fatty acid (SCFA) metabolism and cholesterol metabolism were investigated in four groups of rats fed the following semipurified diets differing in their carbohydrate source: a control diet (purified wheat starch) and three whole cereal flour diets [Valoris wheat (Wv), Soissons wheat (Ws), or Carnac triticale (Tc)]. Wv is particularly viscous and rich in arabinoxylans, and Tc is richer in hemicellulose than wheat. Compared with controls, rats fed the whole-flour diets had enlarged ceca and a moderate acidification of the bulk pH ( approximately 6.4). In these rats, the cecal SCFA pool size was enhanced (P < 0.05), and the SCFA molar ratio reflected propionic/butyric acid-rich fermentations, especially in those fed TC: The portal SCFA concentrations reflected the rise of the acetic and propionic acid pools in the cecum, whereas portal butyric acid remained relatively low, probably reflecting extensive metabolism by the cecal wall. The fecal excretion of total steroids (bile acids + sterols) was markedly enhanced by all of the whole-flour diets, with Wv (+78%) > Tc (+64%) > Ws (+47%). In parallel, there was a significant plasma cholesterol-lowering effect for rats fed Wv (-27%) and Tc (-32%) and a plasma triglyceride-lowering effect (approximately -40%) in all rats fed whole-flour diets (P < 0.05). This effect was observed mainly for triglyceride-rich lipoprotein-cholesterol, whereas HDL cholesterol was unaffected. These results indicate that whole wheat flours can strikingly affect cecal SCFA, especially butyrate, and are effective plasma cholesterol-lowering agents.     

Specific effects of fermentable carbohydrates on blood urea flux and ammonia absorption in the rat cecum

These studies were conducted to determine to what extent dietary fibers, or related compounds such as lactulose or amylomaize starch, alter the flux of blood urea to the cecum and cecal absorption of ammonia in the rat. Cecal weight and pH values were not different among rats fed diets containing 10% lactulose, pectin or guar gum, or 25% amylomaize starch. However, the cecal wall weight was markedly higher with lactulose feeding than with the other polysaccharides, whereas volatile fatty acid concentrations were lower with lactulose. The fiber diets depressed cecal ammonia, particularly in the case of the amylomaize starch diet, whereas the lactulose diet enhanced the concentration of ammonia. Owing to cecal enlargement and enhanced blood flow, the diets containing fermentable carbohydrates promoted a higher flux of urea to the cecum and also higher ammonia absorption in spite of low concentrations of ammonia in the cecum. Lactulose led to particularly high transfer of urea and absorption of ammonia. High blood urea in rats fed a 50% casein diet led to a very high flux of urea to the cecum and, hence, to high ammonia absorption. The presence of polysaccharides amplified the flux of urea and ammonia in the cecum. This study suggests that oligosaccharides such as lactulose, although very effective for the acidification of the contents of the large intestine, may enhance cecal ammonia and its absorption. Polysaccharides such as amylomaize starch might show greater efficiency for lowering ammonia concentrations in the large intestine.     

Dietary fiber-rich barley products beneficially affect the intestinal tract of rats

The objective of this study was to investigate the effects of barley-rich diets in the intestinal tract of rats. Four test groups (A-D) of 10 young male Wistar rats were fed diets containing 50 g/100 g barley extrudates (A, B and D) or mixtures (C) for 6 wk; the control diet contained no barley. The barley-containing supplements in the test diets were: A = cultivar "HiAmi"; B = "HiAmi" and "Prowashonupana" (50:50); C = "Prowashonupana" and Novelose (50:50); D = "Prowashonupana" and amylose from maize (60:40). These supplements contained 7-12 g/100 g beta-glucan and 7-24 g/100 g resistant starch. Additionally, 5 g microcrystalline cellulose/100 g was present in all diets. Carbohydrate utilization (indirect calorimetry) was lower (P < 0.05) in rats fed the barley-containing diets C or D than in the controls. In the test groups, the following differences from the controls were found: greater food intake in the last 2 wk (P < 0.05); increased weight gain in wk 6 (P < 0.05); greater mass of the ceca (groups B-D; P < 0.05) and colons (P < 0.001) as well as masses of cecal (groups C and D; P < 0.01) and colon contents (P < 0.001); greater concentrations of resistant starch in cecal and most of the colon contents (P < 0.05); and more beta-glucan in the small intestine, cecum and colon (P < 0.05). The numbers of coliforms and Bacteroides were lower than in the controls in groups B-D and those of Lactobacillus were greater in all test groups (P < 0.05). Short-chain fatty acids (SCFA) were higher in the cecal contents of the test groups (> or = 800 micro mol/g DM; P < 0.001) compared with the controls ( approximately 200 micro mol/g DM). Similarly, SCFA were higher in colon and feces of the test groups. The concentrations of excreted bile acids increased up to 30% during the feeding period. The proportions of secondary bile acids were lower and the amounts of neutral sterols (P < 0.001) were greater in feces of rats fed the barley-containing diets for 6 wk than in the controls. Diets containing more soluble macromolecular dietary fibers such as beta-glucans affected the excretion of bile acids and neutral sterols the most, whereas the fermentation of dietary fiber, including resistant starch, influenced the steroids in feces. These results suggest that dietary fiber-rich barley-containing diets have beneficial physiologic effects.     

The degree of methylation influences the degradation of pectin in the intestinal tract of rats and in vitro

We investigated the degradation, metabolism, fate, and selected effects of pectin in the intestinal tract of rats. Conventional and germfree rats were fed for 3 wk diets containing 6.5% pectin (degree of methylation 34.5, 70.8 and 92.6%, respectively) or pectin-free diets. Pectin passes the small intestine as a macromolecule. The molecular weight distribution of pectins isolated from intestinal contents of germfree rats were unaffected by diet. No or very little galacturonan was found in cecum, colon or feces of most of the conventional rats. In colon contents of some conventional rats, di- and trigalacturonic acid were present. Total anaerobic and Bacteroides counts were greater in groups fed pectin. The concentration of short-chain fatty acids (SCFA) was higher in cecum and feces in all pectin-fed groups. With increasing degree of methylation, the formation rate of SCFA decreased in the cecum of conventional rats. During in vitro fermentation of pectin with fecal flora from rats, unsaturated oligogalacturonic acids appeared as intermediate products. Low-methoxyl pectin was fermented faster than high-methoxyl pectins in vivo and in vitro. Pectin-fed rats had greater ileum, cecum and colon weights. We conclude that structural parameters of pectin influence its microbial degradation in the intestinal tract.     

Hypolipidaemic effect of maize starch with different amylose content in ovariectomized rats depends on intake amount of resistant starch

The effect of amylose content on digestibility of starch in the small intestine and on the concentration of plasma lipid were studied in ileorectostomized rats and in ovariectomized rats, respectively. Seven kinds of starch with different amylose content (0, 27, 54, 62, 76, 79, 86 %) were used as test starch, which contained 0.4, 5.6, 37.1, 40.2, 45.6, 36.9 and 36.1 % resistant starch (RS), respectively. Rats were fed one of test diets containing 30 % test starch with different amylose content for 14 d in ileorectostomized and for 21 d in ovariectomized rats. Food intake was not significantly different among the groups. In ileorectostomized rats, the small intestinal starch digestibility decreased with increasing intakes of amylose and RS. In ovariectomized rats, body weight gain was lower on the higher amylose maize starch diets. The concentrations of plasma TAG and cholesterol decreased with increasing intake of RS. The concentrations of liver total lipids and TAG decreased with increasing intake of RS, but that of liver cholesterol did not. There was significant positive correlation between the level of sterol regulatory element-binding protein-1c mRNA and concentration of liver TAG. Total SCFA amount in the caecum increased logarithmically with increasing dry weight of caecal contents. The amount of bile acids in the small intestinal content and the excretions of bile acids and neutral steroids in faeces increased with increasing RS intake. These results show that starch rich in RS is more effective in preventing ovarian hormone deficiency-induced hyperlipidaemia.     

Effects of a soluble dietary fibre NUTRIOSE? on colonic fermentation and excretion rates in rats

The resistant dextrin NUTRIOSE®, developed from starch, is expected to act as a prebiotic. The aim of this study was to determine the effects of NUTRIOSE® on cecal parameters, short-chain fatty acid (SCFA) concentrations, and fecal excretion in rats. In an initial experiment, twenty-four male Fischer F344 rats were randomly assigned to one of the following four treatments for 14 days: G0 (control diet), G2.5 (control diet + 2.5% of dextrin), G5 (control diet + 5% of dextrin), and G10 (control diet + 10% of dextrin). After 14 days, total cecal weight, cecal content, and cecal wall weight were significantly increased in G5 and G10 compared to G0. At the same time, cecal pH was significantly lower in G10 compared to G0. Total SCFA concentration was significantly higher in G10 than in G5, G2.5, and G0, and significantly higher in G5 than in G0. Acetate, butyrate, and propionate concentrations were significantly increased in G5 and G10 compared to the controls. In a second trial based on a similar design, eighteen male Fischer F344 rats were treated with a control diet supplemented with 5% of dextrin or 5% of fructo-oligosaccharide. The results obtained with NUTRIOSE® were similar to those obtained with the fructo-oligosaccharide. In a third experiment, two groups of 5 Fischer F344 rats were orally treated with 100 and 1,000 mg/kg NUTRIOSE®, respectively, and from 18% to 25% of the dextrin was excreted in the feces. The results of these three studies show that the consumption of NUTRIOSE®, by its effects on total cecal weight, cecal content, cecal wall weight, pH, and SCFA production, could induce healthy benefits since these effects are reported to be prebiotic effects.