Effect of long term lactulose ingestion on secondary bile salt metabolism in man: potential protective effect of lactulose in colonic carcinogenesis

The interaction of bile acids and gut inflammation influences the pathogenesis of inflammatory bowel disease

Bile acids (BA) are amphipathic molecules originating from cholesterol in the liver and from microbiota-driven biotransformation in the colon. In the gut, BA play a key role in fat digestion and absorption and act as potent signaling molecules on the nuclear farnesoid X receptor (FXR) and membrane-associated G protein-coupled BA receptor-1 (GPBAR-1). BA are, therefore, involved in the maintenance of gut barrier integrity, gene expression, metabolic homeostasis, and microbiota profile and function. Disturbed BA homeostasis can activate pro-inflammatory pathways in the gut, while inflammatory bowel diseases (IBD) can induce gut dysbiosis and qualitative and/or quantitative changes of the BA pool. These factors contribute to impaired repair capacity of the mucosal barrier, due to chronic inflammation. A better understanding of BA-dependent mechanisms paves the way to innovative therapeutic tools by administering hydrophilic BA and FXR agonists and manipulating gut microbiota with probiotics and prebiotics. We discuss the translational value of pathophysiological and therapeutic evidence linking BA homeostasis to gut inflammation in IBD.

Lactulose: Patient- and dose-dependent prebiotic properties in humans

Lactulose is a disaccharide used in clinical practice since 1957 and has since been tested in the treatment of many human disorders, including chronic constipation, hepatic encephalopathy, and chronic kidney disease. Its mode of action is based on the lactulose fermentation by intestinal microbiota. Based on in silico, in vitro and in vivo studies we comprehensively review here the impact of lactulose on human gut/fecal and vaginal microbiota composition and both fecal and blood metabolomes. However, both in vitro and in vivo studies summarized in this review have revealed that the effects of lactulose on human microbiota composition are both patient- and dose-dependent. This highlights the need of heterogeneity indication in clinical trials.

Cimetidine/lactulose therapy ameliorates erythropoietic protoporphyria-related liver injury

A 21-year-old Japanese man was admitted to our hospital because of severe abdominal pain and jaundice. He had been suffering from abdominal pain attacks and liver dysfunction since 18 years of age. Liver histology showed amorphous brown deposits in the sinusoidal space and significant periportal fibrosis without apparent hepatitis. Increased protoporphyrin in serum and feces and ferrochelatase gene mutation confirmed the final diagnosis of erythropoietic protoporphyria (EPP). Since ursodeoxycholic acid (UDCA) intake and glucose infusion are insufficient to ameliorate jaundice and abdominal attacks, cimetidine and lactulose were added in order to suppress hepatic delta-aminolevulinic acid synthase and limit re-absorption of protoporphyrin, respectively. Afterwards, the jaundice, liver dysfunction and abdominal symptoms improved and UDCA, cimetidine, and lactulose administration was continued. A repeat biopsy at 1.5 years after adding cimetidine/lactulose revealed marked attenuation of periportal fibrosis and protoporphyrin deposits. As far as we know, this is the first demonstration of histological improvement of EPP-induced liver abnormalities due to persistent cimetidine/lactulose administration. These treatments may be useful for EPP-related liver injury.

Galacto-oligosaccharides and Colorectal Cancer: Feeding our Intestinal Probiome

Prebiotics are ingredients selectively fermented by the intestinal microbiota that promote changes in the microbial community structure and/or their metabolism, conferring health benefits to the host. Studies show that β (1-4) galacto-oligosaccharides [β (1-4) GOS], lactulose and fructo-oligosaccharides increase intestinal concentration of lactate and short chain fatty acids, and stool frequency and weight, and they decrease fecal concentration of secondary bile acids, fecal pH, and nitroreductase and β-glucuronidase activities suggesting a clear role in colorectal cancer (CRC) prevention. This review summarizes research on prebiotics bioassimilation, specifically β (1-4) GOS, and their potential role in CRC. We also evaluate research that show that the impact of prebiotics on host physiology can be direct or through modulation of the gut intestinal microbiome, specifically the probiome (autochtonous beneficial bacteria), we present studies on a potential role in CRC progression to finally describe the current state of β (1-4) GOS generation for industrial production.

Inulin prolongs survival of intragastrically administered Lactobacillus plantarum No. 14 in the gut of mice fed a high-fat diet

We tested whether a high-fat diet (HFD) impairs the survival of probiotics in mice. In Expt. 1, after feeding either a HFD (62.7% energy) or a normal-fat diet (NFD; 11.1% energy) for 2 d, C57BL/6 mice were i.g. administered Lactobacillus plantarum No. 14. Fecal recovery of viable L. plantarum was significantly decreased 99% by the HFD compared with the NFD. Total bile acid concentrations in the small intestine and cecum were significantly higher (1.5- and 2.2-fold of NFD, respectively) in mice fed HFD than in those fed NFD. Cholic acid and deoxycholic acid significantly reduced the viability of L. plantarum No. 14 in culture experiments. In Expt. 2, after feeding HFD for 2 d, simultaneous administration of inulin (10 mg) with L. plantarum No. 14 significantly increased (100-fold of that without inulin) the fecal recovery of viable L. plantarum. Inulin administration did not alter intestinal bile acid concentrations. In Expt. 3, after feeding HFD for 2 d, mice were i.g. administered either inulin (10 mg) or vehicle and, after 6 h, cecal contents were subjected to culture experiments. Growth of L. plantarum No. 14 was significantly higher in the cecal contents of inulin-administered mice than vehicle-administered mice. Inulin supplementation to cecal contents of vehicle-administered mice significantly enhanced the growth of L. plantarum No. 14. We propose that HFD impairs the survival of probiotics in the gut due to increased bile acid stress and that simultaneous administration of inulin prolongs the survival of probiotics in mice fed HFD.

Evaluation of relationships among national colorectal cancer mortality rates, genetic lactase non-persistence status, and per capita yearly milk and milk product consumption

Colorectal cancer (CRC) is one of the leading causes of mortality in Western countries. Its putative pathogenesis revolves around genetic and environmental factors, particularly diet. One of the most studied dietary factors, dairy product intake, is still debated as a protective agent. The role of lactose as a candidate prebiotic (stimulating lactic acid bacteria) and its relation to genetic lactase non-persistence (LNP) status has not been evaluated. We undertook a review and analysis of national per capita dairy product consumption, national LNP prevalence, and national CRC mortality rates (CRCM) to determine whether relationships existed among these variables. Data on these three items were obtained from the available literature. A negative binomial regression model was used to compare national LNP status with national CRCM rates for three time periods. Pearson correlation was used to compare national per capita dairy food intake with national CRCM rates for the approximate midpoint time period of reviewed articles. We found that there was a significant positive correlation between per capita dairy food intake and CRCM rates. However, there was also a significant negative correlation between national LNP prevalence and CRCM rates. Population-based studies supported the suggestion that in both homogeneous high and homogeneous low prevalence LNP countries characterized by low and high dairy food intake respectively, dairy food consumption exerted a protective effect against CRC and CRCM rate. Because some population studies contradict the hypotheses that dairy food intake promotes CRC or that LNP status protects against CRC, we hypothesize that dairy food consumption may operate by two distinct mechanisms--one that operates at low doses in LNP subjects and another in high doses in non-LNP subjects.

Lactulose ingestion increases faecal bifidobacterial counts: a randomised double-blind study in healthy humans

OBJECTIVE

Faecal bifidobacteria and lactobacilli, perceived as exerting health-promoting properties, may be increased by ingestion of high-dose lactulose in humans. The effects of low and well-tolerated doses of lactulose are not well known. The aim of the study was to assess the effects of prolonged low-dose lactulose administration on faecal bifidobacteria and selected metabolic indexes potentially involved in colonic carcinogenesis.

SUBJECTS AND METHODS

In all, 16 healthy volunteers were included in this controlled, randomised, double-blind, parallel group trial. Participants ingested lactulose or placebo (sucrose) at a dose of 5 g b.i.d. for 6 weeks. Stools were regularly collected at baseline (d0), and after 3 (d21) and 6 (d42) weeks of sugar ingestion. Tolerance was evaluated using a daily chart.

RESULTS

Faecal bifidobacterial counts were higher in lactulose than in sucrose group (P=0.03). Lactulose ingestion led to a significant increase in faecal bifidobacteria counts from d0 to d21 and d42 ((m+/-s.e.m.) 8.25+/-0.53, 8.96+/-0.40 and 9.54+/-0.28 log colony-forming units/g wet wt (CFU/g), respectively (P=0.048)). Placebo ingestion did not lead to any faecal bifidobacterial count change. Total anaerobes, Lactobacillus and pH were not significantly changed throughout the study in the two groups. Neither faecal bile acids nor neutral sterols were modified by lactulose. Excess flatus was more common in the lactulose group (P=0.03), but was very mild. Bloating and borborygmi did not differ between both the groups.

CONCLUSIONS

A measure of 10 g lactulose/day increases faecal bifidobacterial counts, and lactulose fulfils the criteria requested to be considered as a prebiotic.

Review article: lactose--a potential prebiotic

Lactose maldigestion, which affects a large majority of the world's population, has been mostly linked with uncomfortable symptoms. In addition, dairy consumption is variably blamed or recommended for a number of ill effects. There is, however, emerging evidence that certain lactic acid-producing bacteria, which selectively consume prebiotics, may be beneficial against some lower intestinal diseases. Lactose maldigestion and lactose should perhaps be re-evaluated as a potential provider of such a prebiotic. This historical and observational review discusses lactose and argues the opinion that it has prebiotic potential. Moreover, in maldigesters, natural ingestion or lack thereof may be relevant in the pathogenesis of diseases such as colorectal cancer and inflammatory bowel diseases.

Influence of pH on the phase distribution of nascent deoxycholic acid in fresh human cecal aspirates

Prolonged large bowel transit time and an associated increase in the proportion of deoxycholic acid (DCA) in serum and bile have been implicated in the development of cholesterol-rich gallstones and colon cancer. Prolongation of intestinal transit also increases intracolonic pH that, we hypothesized, should favor the solubilization and absorption of newly formed DCA within the colon. To test this hypothesis, we performed in vitro studies on homogenized cecal aspirates (obtained at colonoscopy) that were incubated anaerobically with [14C]cholic acid for 16 h after which the pH was adjusted to between 4.0 and 7.0 in 0.5-pH unit steps. The resultant reaction mixtures were centrifuged to separate the supernatant from the precipitate, and the specific activity of [14C]DCA was quantitated in both phases. As the pH in the aspirates was manipulated from 4.0 to 7.0, the proportion of newly formed, labeled DCA increased in the supernatant and fell in the precipitate, particularly at a hydrogen ion concentration of <100 x 10(-7) (equivalent to pH 5.0-7.0). These results show that the solubility of DCA in colonic contents increases with increasing pH. If solubility is rate limiting, this should lead to increased absorption that, in turn, would explain why the proportion of DCA in serum and bile increases with the prolongation of large bowel transit time.

Improved parameters of lactose maldigestion using lactulose

Lactulose is a disaccharide derived from lactose. There has been recent rekindling of interest in the possible benefits of pro- and prebiotics: mainly, lactic acid-producing bacteria and lactulose for the lower intestine. Since lactose maldigestion is a common genetic trait, we undertook this study to delineate similar effects between these two disaccharides. Nine healthy lactose maldigesting subjects underwent two separate periods of three weeks adaptation, first with 10 g twice daily lactulose and then 1.5 g twice daily lactose (in milk). Adaptation was defined by reduced breath Hydrogen (BH2) and symptoms after 50 g lactose challenges. In six subjects fecal beta-galactosidase was measured. All subjects consumed some lactose daily. In the first period, eight subjects improved symptoms and reduced BH2 significantly, while in the second period they did not. Fecal beta-galactosidase significantly increased after lactulose. This study supports the notion that lactulose and lactose may have similar clinical effects.

Dietary maltitol decreases the incidence of 1,2-dimethylhydrazine-induced cecum and proximal colon tumors in rats

Maltitol is fermented in the colon due to only partial hydrolysis in the small intestine. In the present study, we examined effects of dietary maltitol on dimethylhydrazine-induced intestinal tumor in rats. In experiment 1, rats were fed a fiber-free diet or diets supplemented with 1 or 5 g/100 g maltitol for 27 wk. Each group of rats was injected with dimethylhydrazine or vehicle alone for the first 14 wk of the experimental period. Maltitol supplementation at 1 g/100 g of the diet significantly reduced tumor incidence in the cecum and the 5% supplement reduced tumor incidence in both the cecum and proximal colon in dimethylhydrazine-treated rats. In experiment 2, we investigated the effect of the 1 g/100 g maltitol diet on the short chain fatty acid concentrations in cecal contents of placebo and dimethylhydrazine-treated rats. Intake of the 1 g/100 g maltitol diet doubled (P < 0.05) the concentration of butyrate but did not affect acetate or propionate in the cecal contents. These results suggest that dietary maltitol has a protective effect against dimethylhydrazine-induced tumors in rat cecum and proximal colon and that butyrate produced by bacterial fermentation of maltitol in the cecum may be involved in the protection.

Effect of lactulose and fiber-rich diets on bile in relation to gallstone disease: an update

The primum movens in cholesterol gallstone formation is hepatic cholesterol hypersecretion and chronic supersaturation of bile. From this event a cascade of contributing factors can be differentiated: (i) Motility defects with impaired gallbladder contractility and gallbladder stasis, but also with small and large intestinal hypomotility. (ii) Multiple biochemical defects in gallbladder bile with increased biliary proteins, increased deoxycholic acid and rapid crystallization of biliary cholesterol from supersaturated unstable vesicles. There is considerable evidence that slow intestinal and colonic transit can increase the deoxycholic acid pool size and biliary cholesterol saturation. Changes in intestinal transit influence the anaerobic bacterial enzymatic biotransformation of conjugated cholate to more hydrophobic deoxycholate. This leads to biliary cholesterol hypersecretion and gallstone formation. Prokinetic drugs or administration of lactulose or fiber products like bran can change the slow intestinal transit favourably with subsequent reduction in deoxycholic acid formation and cholesterol saturation of bile. Whether these applications are indeed of value in the long-term prevention of gallstone disease, however, is doubtful, since fiber-rich diet in prevention of gallstone recurrence after complete gallstone dissolution was not successful.

A clinical hepatologist's predictions about non-absorbed carbohydrates for the early twenty-first century

To put these predictions into perspective, the primary indication for lactulose therapy in the treatment of HE and SHE is presented and discussed. Six secondary indications for lactulose therapy are also listed and briefly commented upon. A dozen predictions about the status of lactulose are presented and briefly discussed. A. Lactulose will be the treatment of choice for HE.B. TIPS will be the most common cause of HE.C. Lactulose will not be approved in Mexico. D. Lactulose plus anti-diarrheal drugs will be agents for treatment of HE. E. Lactulose will not be the treatment of choice for constipation. F. Lactulose will not be used for Salmonella or Shigella carrier states. G. Lactulose will be routinely administered prophylactically after TIPS. H. Lactulose will be administered prophylactically to cirrhotic patients with portal hypertension. I. Lactulose plus anti-diarrheal drugs will be used for a variety of diverse purposes: (i) Suppression of bacterial growth; (ii) prevention of bacteriuria; (iii) diminution of cholesterol saturation of bile; (iv) adjunct treatment of gallstones with ursodeoxycholic acid; (v) Prevention of colon carcinoma.

Effects of acarbose on fecal nutrients, colonic pH, and short-chain fatty acids and rectal proliferative indices

Acarbose, an alpha-glycosidase inhibitor, treats diabetes mellitus by delaying the digestion and intestinal absorption of dietary carbohydrates. In effective doses, acarbose induces some passage of carbohydrates into the colon. The effect of such chronic carbohydrate transfer on colonic structure and function is unknown. We studied the effects of 1 year of acarbose administration in diabetes mellitus on fecal energy, protein, and fat, including short-chain fatty acids (SCFA) output, fecal pH, and several metabolizing bacterial species. Changes in colonic histology and epithelial cell proliferation were investigated in rectal biopsies. Fecal macronutrient output was unaffected by acarbose, but pH decreased and total SCFA, butyrate, and acetate output were markedly greater. Breath hydrogen output increased after acarbose, but digoxin-metabolizing bacteria and diacylglycerol (DAG) production were unaltered. Compared with the control, acarbose did not induce hyperplasia or change rectal proliferation. However, total fecal SCFA and butyrate output correlated inversely with proliferation in the rectal upper crypt-a biomarker of risk for colonic neoplasia. In conclusion, long-term acarbose administration does not adversely affect colonic function or fecal nutrient output. If increased fecal SCFA and butyrate reduces upper-crypt proliferation, then acarbose may reduce the risk of colonic neoplasia.

Effect of two levels of transgalactosylated oligosaccharide intake in rats associated with human faecal microflora on bacterial glycolytic activity, end-products of fermentation and bacterial steroid transformation

The effects of two levels of transgalactosylated oligosaccharide (TOS) intake on bacterial glycolytic activity, end products of fermentation and bacterial steroid transformation were studied in rats associated with a human faecal flora. Rats were fed a human-type diet containing 0, 5 or 10% TOS. Caecal pH decrease correlated with the amount of TOS in the diet. Intake of the TOS diet induced a decrease in blood cholesterol and a strong increase in beta-galactosidase activity in the hindgut. TOS fermentation led to production of hydrogen and short chain fatty acids, whereas ammonia and branched-chain fatty acids were decreased. A diet containing 10% TOS increased caecal lactic acid concentrations and reduced beta-glucuronidase activities and steroid transformation.

Effects of fructo-oligosaccharides ingestion on fecal bifidobacteria and selected metabolic indexes of colon carcinogenesis in healthy humans

Fructo-oligosaccharides (FOS) are a mixture of oligosaccharides consisting of glucose linked to fructose units. They are not digested in the human small intestine but fermented in the colon, where they could specifically promote the growth of some species of the indigenous microflora, especially bifidobacteria. We assessed in healthy humans the effects of FOS ingestion in fecal bifidobacteria and selected metabolic indexes potentially involved in colonic carcinogenesis. Twenty volunteers randomly divided into two groups were studied for three consecutive 12-day periods. During the ingestion period, they received 12.5 g/day FOS or placebo (saccharose) in three oral doses. Stools were regularly collected and analyzed. FOS ingestion led to an increase in fecal bifidobacterial counts [7.9 +/- 0.5 to 9.1 +/- 0.3 (SE) log colony-forming units/g wet wt, p < 0.01] and beta-fructosidase activity (9.6 +/- 1.9 to 13.8 +/- 1.9 IU/g dry wt, p < 0.01). In contrast, FOS ingestion had no significant effect on fecal total anaerobes, pH, the activities of nitroreductase, azoreductase, and beta-glucuronidase, and the concentrations of bile acids and neutral sterols. We conclude that ingestion of FOS, at a clinically tolerated dose of 12.5 g/day, led to an increase in colonic bifidobacteria. This effect was not associated in healthy humans with beneficial changes in various factors potentially involved in the pathogenesis of colonic cancer.

Wheat fibre, lactulose and rectal mucosal proliferation in individuals with a family history of colorectal cancer

In a single-blind study 38 individuals at increased risk of developing colorectal cancer because of a family history of the disease were randomized to take 10.5 g wheat fibre (Trifyba) or 60 ml lactulose daily for 12 weeks. Rectal biopsies were taken before and after treatment and rectal mucosal proliferation was measured by the crypt cell production rate (CCPR). The mean(s.d.) CCPR was significantly lower in those taking wheat fibre after 12 weeks (7.2(3.4) crypt cells per crypt per h) compared both with values obtained before treatment with wheat fibre (10.2(5.1) crypt cells per crypt per h; P = 0.02) and after treatment with lactulose (9.4(3.8) crypt cells per crypt per h; P = 0.05). Proliferation in the lactulose group was not significantly different at 12 weeks compared with the value obtained before treatment. This study confirms an antiproliferative effect of wheat fibre in a group of high-risk individuals.

Effect of resistant starch on colonic fermentation, bile acid metabolism, and mucosal proliferation

Resistant starch is by definition that part of starch that escapes digestion in the small bowel. Cecal fermentation of resistant starch into short-chain fatty acids will result subsequently in a decrease in pH. Thus, resistant starch may have the same effect on colonic luminal contents and mucosa as some fiber components. We studied the effects of adding 45 g native amylomaize (Hylon-VII) to a standardized diet in 14 healthy volunteers on fermentation and colonic mucosal proliferation. Hylon-VII is a high amylose maize starch, containing 62% resistant starch. During amylomaize consumption, breath hydrogen excretion rose 85% and fecal short chain fatty acid output increased 35% (P < 0.01). Excretion of primary bile acids increased and the soluble deoxycholic acid concentration decreased by 50% (P = 0.002). Subsequently, cytotoxicity of the aqueous phase of feces--as measured on a colon cancer cell line--decreased (P = 0.007). Colonic mucosal proliferation in rectal biopsies (proliferating cell nuclear antigen immunostaining) decreased from 6.7 to 5.4% (P = 0.05). We speculate that resistant starch consumption decreases colonic mucosal proliferation as a result of the decreased formation of cytotoxic secondary bile acids, which is possibly mediated through acidification of the large bowel by production of short-chain fatty acids.

Antioxidant vitamins or lactulose for the prevention of the recurrence of colorectal adenomas. Colorectal Cancer Study Group of the University of Modena and the Health Care District 16

Colonic adenomas represent the natural precursor lesions of most colorectal cancers. The treatment of choice is endoscopic polypectomy. However, after endoscopic removal, polyps recur in a large fraction of cases. Thus, we evaluated the effect of antioxidant vitamins or lactulose on the recurrence rate of adenomatous polyps. After polypectomy, 255 individuals were randomized into three groups. Group 1 was given vitamin A (30,000 IU/day), vitamin C (1 g/day), and vitamin E (70 mg/day); Group 2 was given lactulose (20 g/day); Group 3 received no treatment. Forty-six subjects had to be excluded because the histologic diagnosis was not consistent with adenoma. The remaining 209 individuals were included in the analysis according to the "intention to treat" criterion, though 34 did not adhere to the scheduled treatment or were lost during the follow-up. Subjects were followed at regular intervals for an average of 18 months. Polyps recurring before one year from index colonoscopy were considered missed by the endoscopist. In the 209 evaluable subjects, the percentages of recurrence of adenomas were 5.7 percent, 14.7 percent, and 35.9 percent in the vitamins, lactulose, and untreated groups, respectively. The fraction of subjects remaining free of adenomas, estimated by Kaplan-Meier survival curves, was significantly different among the three groups (log-rank chi-squared = 17.138; P < 0.001). Using Cox's regression analysis, treatment was the only variable that significantly contributed to the model (regression coefficient = 0.905; P < 0.001). In conclusion, either antioxidant vitamins or, to a lesser extent, lactulose lower the recurrence rate of adenomas of the large bowel and can be proposed as chemopreventive agents, at least in high-risk individuals.

The role of carbohydrate fermentation in colon cancer prevention

Diet is an important factor in the development of colonic cancer. Fibre has been shown to decrease this risk. Part of this protective effect is probably mediated by colonic fermentation. About 10% of starch in the normal diet escapes digestion and absorption in the small bowel, and is therefore called resistant starch. This is a considerably larger source of fermentable substrate than fibre in the diet and could thus contribute significantly to the prevention of this malignancy. Short chain fatty acids, produced during fermentation, reduce colonic pH, affecting the intraluminal concentration of the putative co-carcinogenic secondary bile acids by precipitation, and by inhibition of their enzymatic formation from primary bile acids. The role of secondary bile acids in promoting colonic carcinogenesis is probably mediated by their cytotoxic effect on colonic mucosa, leading to a compensatory increase in proliferation. A hyper-proliferative mucosa, having an enhanced sensitivity to mutagenic substances, is associated with an increased risk of colorectal cancer. Butyrate, one of the short chain fatty acids, could be significant, as it has anti-neoplastic properties in vitro and in vivo. We conclude that fermentation is probably the key factor in the protective effect of fibre on colon carcinogenesis. Furthermore, consumption of resistant starch seems to be another way of stimulating fermentation.

Long-term effect of Bifidobacteria and Neosugar on precursor lesions of colonic cancer in CF1 mice

This investigation was undertaken to study the role of Bifidobacteria and bifidogenic factor Neosugar in the process of 1,2-dimethylhydrazine-induced colonic carcinogenesis in CF1 mice. Intestinal colonization and selective proliferation of Bifidobacteria were achieved by oral administration of indigenous Bifidobacteria and the incorporation of 5% Neosugar in the diet of animals. The Bifidobacteria were isolated from the feces of CF1 mice and were identified to be Bifidobacterium pseudolongum biovar b. This incidence of aberrant crypts and foci were significantly lower 38 weeks after the last injection of the carcinogen in animals fed Bifidobacteria than in animals treated with the carcinogen alone. The aberrance also appeared to be confined to the more distal end of the colon in animals fed bifidogenic diet. Such changes in the precursor lesions of colonic carcinogenesis are presumably due to the increase in the number of Bifidobacteria and their acidifying action in the lower intestinal tract of the animals.

Determinants and consequences of colonic luminal pH: implications for colon cancer

Epidemiological data suggest that increased risk of colon cancer is correlated with a higher fecal pH. Although some experimental studies have shown a protective effect against experimentally induced colon cancer by acidifying colonic contents, others have shown that a more acidified colonic content is associated with increased cell proliferation and enhanced tumorigenesis. It is now clear that simply acidifying colonic contents will not consistently result in decreased tumorigenesis. Perhaps the key is how colonic contents are acidified--a decrease in base production or an increase in acid production. Or, more important than luminal pH itself, may be a factor affected by changes in hydrogen ion concentration. This paper reviews the determinants of colonic luminal pH and their dietary sources and discusses important physiological consequences of modifying the pH of colonic contents.