Changing concepts of dietary fiber: implications for carcinogenesis

Lignocellulose, dietary fibre, inulin and their potential application in food

In recent years, due to food insecurity, lignocellulose, dietary fibre as well as inulin have received wider attention owing to their abundance and being relatively low-cost indigestible polysaccharides. Since the recognition, acceptance of the consumption and utilization of these polysaccharides, as well as their attraction in science and industry has grown tremendously. There have been further researches carried out to ascertain the fact that people who consume or utilize these polysaccharides have low exposure to some fatal life-threatening illnesses. Rich sources of indigestible polysaccharides such as vegetables, cereals, fruits and nuts are beneficial to good health as consuming them reduce the occurrence of degenerating diseases such as colon cancer, heart disease, diabetes, etc. Despite these increasing facts depicting their advantages in the state of human health, their intake and utilization still fall below the acceptable limit and the knowledge of how they work in the human body are minimal with their explicit actions not easily shown. Hence, this review gives a better understanding of the significance of lignocellulose, dietary fibre and inulin, their functions, classifications, types and applications in the food industry, thereby exposing their various uses as these polycarbohydrates were considered a waste before now.

Sunroot snack bar: Optimization, characterization, consumer perception, and storage stability assessment

This study reports the evolution of phenolics, inulin content, proximate composition, hardness, and sensory characteristics of an inulin-rich healthy snack bar (The Sunroot Snack Bar) over 90 days of storage in refrigerated and room temperature storage. A response surface methodology (RSM) with a central composite rotatable design was first employed for optimizing the concentrations of sunroot, potato, and oats. The optimum selected concentrations of sunroot, potato, and oat were 53.99, 37.88, and 5 g, respectively, and a quadratic model was found to yield the best fit. Analysis of variance revealed that a higher sunroot content resulted in more firmness of the bar and higher overall acceptability in sensory trials. Sunroot snack bar samples without flavor (control), sunroot snack bar with cheese flavor (S1), and sunroot snack bar with olive flavor (S2) were then tested for sensory, chemical, phytochemicals, and microbial contents among control, S1, and S2 samples over a 90-day shelf-life study. Results showed no significant (p < .05) changes in these contents on addition of flavor. An increase in microbial load and the appearance of a bitter taste after 30 days of fresh sunroot storage were observed. No microbial growth was observed in all sunroot snack bar samples during storage at 4°C, while some microbial growth was observed at 25°C for 90 days. It was inferred that the high-quality shelf life of the sunroot bar was 90 days at 4°C, which was shortened to a month if the bars were preserved at 25°C. There was a significant phenolic and inulin content loss at 25°C compared with 4°C in total phenolic component. Based on the results of sensory evaluation, online questionnaire of customer experience, and cost analysis, this study successfully used sunroot tubers for the production of snack bars as a promising new raw material, which was introduced healthily with a suitable price for such product compared with other products in the market.

Plant cell wall chemistry: implications for ruminant utilisation

Ruminants have adapted to cope with bulky, fibrous forage diets by accommodating a large, diverse microbial population in the reticulo-rumen. Ruminants are dependent on forages as their main sources of energy and other nutrients. Forages are comprised of a complex matrix of cellulose, hemicellulose, protein, minerals and phenolic compounds (including lignin and tannins) with various linkages; many of which are poorly defined. The composition and characteristics of polysaccharides vary greatly among forages and plant cell walls. Plant cell walls are linked and packed together in tight configurations to resist degradation, and hence their nutritional value to animals varies considerably, depending on composition, structure and degradability. An understanding of the inter-relationship between the chemical composition and the degradation of plant cell walls by rumen microorganisms is of major economic importance to ruminant production. Increasing the efficiency of fibre degradation in the rumen has been the subject of extensive research for many decades. This review summarises current knowledge of forage chemistry in order to develop strategies to increase efficiency of forage utilisation by ruminants.

Intake of Polydextrose Alters Hematology and the Profile of Short Chain Fatty Acids in Partially Gastrectomized Rats

Polydextrose (PDX) ingestion may increase the intestinal absorption of iron. This study evaluated the effects of 7.5% polydextrose supplementation on markers of iron uptake, transport and storage in partially gastrectomized rats. Half of a batch of 40 male Wistar rats (250 g) underwent Billroth II partial gastrectomy with anterior truncal vagotomy (GXT), while the other half underwent sham gastrectomy (SHAM). At 7 postoperative days, the animals were subdivided into four groups (n = 10): Sham Control and GXT Control (no polydextrose); Sham PDX and GXT PDX (with 7.5% PDX). The animals were euthanized after 60 day of PDX treatment. Organ weight, cecal pH, the characterization and quantification of short-chain fatty acids (SCFA), hematological parameters, hepatic iron content and the expression of ferroportin (FPT) in the jejunum, cecum, colon and liver were evaluated. PDX caused changes in the cecum of the supplemented animals, where there was a decrease in pH, increase in cecal wall and marked production of SCFA, especially acetic and propionic acids (p < 0.05). Hepatic iron levels were lower in GXT animals. PDX increased hemoglobin (HGB) values by 29.2% and hematocrit (HCT) by 55.8% in the GXT PDX group compared to the GXT Control group. The GXT PDX group had lower hepatic FPT expression (p < 0.05). PDX led to increased SCFA concentration in the supplemented animals. Considering that SCFAs play a central role in the increasing nutrients uptake, this mechanism may be involved in altering the hematology profile observed in these animals but not enough to reverse iron deficiency anemia in post-gastrectomy rats.

Reabsorption in the proximal tubuli-ultrastructural evidence for a novel aspect of renal VEGF trafficking

Many clinical and experimental studies have revealed VEGF as an important factor in the pathophysiology of renal damage during diabetes mellitus (DM). Anti-VEGF therapy is in clinical use for treatment of DM and other diabetes-related (and unrelated) diseases. Nevertheless, little is known about the metabolism of VEGF in the kidneys. In order to determine the ultrastructural localization of VEGF in the kidney, we study the distribution of VEGF in the kidney of rats by using immunogold immunohistochemistry. Our light-microscopic data showed remarkable re-distribution of VEGF in proximal tubular cells (PTCs) during prolonged hyperglycemia, a DM type 2 model (DM2), which was confirmed by transmission electron microscopy (TEM) findings. TEM findings revealed an initial presence of VEGF in the vesicular transport apparatus of PTCs in healthy rats and its gradual translocation to the apical membrane of PTCs after renal damage caused by high sucrose treatment. The presented data add to our understanding of kidney VEGF trafficking, providing novel insight into the renal metabolism and pharmacodynamics of the cytokine. This could have a high impact on the use of VEGF and anti-VEGF therapy in different renal diseases.

Dietary fiber intake and head and neck cancer risk: A pooled analysis in the International Head and Neck Cancer Epidemiology consortium

The possible role of dietary fiber in the etiology of head neck cancers (HNCs) is unclear. We used individual-level pooled data from ten case-control studies (5959 cases and 12,248 controls) participating in the International Head and Neck Cancer Epidemiology (INHANCE) consortium, to examine the association between fiber intake and cancer of the oral cavity/pharynx and larynx. Odds Ratios (ORs) and their 95% Confidence Intervals (CIs) were estimated using unconditional multiple logistic regression applied to quintile categories of non-alcohol energy-adjusted fiber intake and adjusted for tobacco and alcohol use and other known or putative confounders. Fiber intake was inversely associated with oral and pharyngeal cancer combined (OR for 5th vs. 1st quintile category = 0.49, 95% CI: 0.40-0.59; p for trend <0.001) and with laryngeal cancer (OR = 0.66, 95% CI: 0.54-0.82, p for trend <0.001). There was, however, appreciable heterogeneity of the estimated effect across studies for oral and pharyngeal cancer combined. Nonetheless, inverse associations were consistently observed for the subsites of oral and pharyngeal cancers and within most strata of the considered covariates, for both cancer sites. Our findings from a multicenter large-scale pooled analysis suggest that, although in the presence of between-study heterogeneity, a greater intake of fiber may lower HNC risk.

Green tea phenolics inhibit butyrate-induced differentiation of colon cancer cells by interacting with monocarboxylate transporter 1

Diet has a significant impact on colorectal cancer and both dietary fiber and plant-derived compounds have been independently shown to be inversely related to colon cancer risk. Butyrate (NaB), one of the principal products of dietary fiber fermentation, induces differentiation of colon cancer cell lines by inhibiting histone deacetylases (HDACs). On the other hand, (-)-epicatechin (EC) and (-)-epigallocatechin gallate (EGCG), two abundant phenolic compounds of green tea, have been shown to exhibit antitumoral properties. In this study we used colon cancer cell lines to study the cellular and molecular events that take place during co-treatment with NaB, EC and EGCG. We found that (i) polyphenols EC and EGCG fail to induce differentiation of colon adenocarcinoma cell lines; (ii) polyphenols EC and EGCG reduce NaB-induced differentiation; (iii) the effect of the polyphenols is specific for NaB, since differentiation induced by other agents, such as trichostatin A (TSA), was unaltered upon EC and EGCG treatment, and (iv) is independent of the HDAC inhibitory activity of NaB. Also, (v) polyphenols partially reduce cellular NaB; and (vi) on a molecular level, reduction of cellular NaB uptake by polyphenols is achieved by impairing the capacity of NaB to relocalize its own transporter (monocarboxylate transporter 1, MCT1) in the plasma membrane. Our findings suggest that beneficial effects of NaB on colorectal cancer may be reduced by green tea phenolic supplementation. This valuable information should be of assistance in choosing a rational design for more effective diet-driven therapeutic interventions in the prevention or treatment of colorectal cancer.

Flaxseed (Linum usitatissimum L.) and its total non-digestible fraction influence the expression of genes involved in azoxymethane-induced colon cancer in rats

The influence of flaxseed (Linum usitatissimum L.) and its total non-digestible fraction (TNDF) on the expression of genes involved in azoxymethane (AOM)-induced colon cancer in Sprague Dawley rats was analyzed. The dose used in the animal model was two tablespoons of flaxseed per day, which is the dose recommended for humans. Flaxseed significantly decreased the crypt multiplicity (10.50 ± 3.5) compared with the AOM treatment (34.00 ± 11.0), which suggests that flaxseed exhibits a preventive effect against colon cancer. Both treatments (flaxseed and TNDF) influence the overexpression of genes involved in cell cycle arrest and mitochondrial apoptosis: p53, p21, bcl-2, bax and caspase-3. Flaxseed induced the expression of p53 and p21, whereas TNDF triggered the p21-independent expression of p53. This finding suggests that both of these treatments induced cell cycle arrest. In addition, TNDF induced mitochondrial apoptosis because the TNDF + AOM group exhibited the expression of caspase-3, decreased bcl-2 expression and increased bax expression. These results suggest that the expression of the analyzed genes is associated with the presence of dietary antioxidants linked to the cell wall of flaxseed.

Dietary roles of non-starch polysaccharides in human nutrition: a review

Nonstarch polysaccharides (NSPs) occur naturally in many foods. The physiochemical and biological properties of these compounds correspond to dietary fiber. Nonstarch polysaccharides show various physiological effects in the small and large intestine and therefore have important health implications for humans. The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentibility into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colo-rectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes. Moreover, a major proportion of dietary NSPs escapes the small intestine nearly intact, and is fermented into SCFAs by commensal microflora present in the colon and cecum and promotes normal laxation. Short chain fatty acids have a number of health promoting effects and are particularly effective in promoting large bowel function. Certain NSPs through their fermented products may promote the growth of specific beneficial colonic bacteria which offer a prebiotic effect. Various modes of action of NSPs as therapeutic agent have been proposed in the present review. In addition, NSPs based films and coatings for packaging and wrapping are of commercial interest because they are compatible with several types of food products. However, much of the physiological and nutritional impact of NSPs and the mechanism involved is not fully understood and even the recommendation on the dose of different dietary NSPs intake among different age groups needs to be studied.

Diet and nutrient factors in colorectal cancer risk

Diet and nutrition are estimated to explain as much as 30%-50% of the worldwide incidence of colorectal cancer. In 2007, the World Cancer Research Fund (WCRF), in conjunction with the American Institute for Cancer Research (AICR), released the second expert report that summarizes the current scientific evidence linking diet to the prevention of cancer. This text provides an expert summary and level of evidence of the research relating diet/nutrients to factors that influence cancers of multiple organs, including colon and rectum, with an important emphasis on global patterns. Specific examples include dietary fat, red and processed meat, and dairy, as well effects of nutrients such as calcium, folate, and vitamin D. Evidence is obtained from ongoing systematic literature reviews conducted by experts in both the United States and Europe. The expert panel applies standard practices to evaluate the strength and quality of individual studies to draw summary conclusions. In 2011, the report was updated to include findings from a series of meta-analyses published in 2010. To complement the WCRF/AICR report, the authors review the evidence favoring the role for diet and nutrition in the etiology of colorectal cancer. Specifically, they have integrated information gained from more recent meta-analyses and high-quality, prospective study findings, some of which have been included in the 2011 updated WCRF/AICR summary.

Inhibition or enhancement by 4 Pacific Island food plants against cancers induced by 2 amino-3-methylimidazo[4,5-f]quinoline in male Fischer 344 rats

A 1-yr carcinogenicity bioassay was conducted in rats fed 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), simultaneously with AIN-76/ high-fat (HF) diet alone, or with 10% starch replaced with kumara, pineapple, coconut, or taro, prepared as for a human diet. All of the non-IQ treated control, kumara, pineapple, or taro but not coconut-fed rats survived to 1 yr. None of the IQ-fed animals survived to 1 yr and although there were minor survival time differences among the groups, none was statistically significant. At sacrifice, IQ/HF controls had tumors in the skin, Zymbal's gland, ear canal, oral cavity, liver, and small intestine, totaling 32 among 20 animals. Kumara-fed rats had a similar tumor distribution but no tumors in the ear or oral cavity, and a total of 27 tumors among 20 animals, whereas pineapple-fed rats showed a somewhat lower tumor incidence (23/20 animals), including no small intestine lesions. Unexpectedly, a higher tumor incidence, especially of skin tumors, was seen in coconut and taro-fed animals (35/20 and 41/20 animals, respectively). In particular, the incidence of malignant liver tumors and gastrointestinal tumors were significantly increased in the taro-fed group in comparison with the kumara group.

Chemopreventive effects of in vitro digested and fermented bread in human colon cells

PURPOSE

Bread as a staple food product represents an important source for dietary fibre consumption. Effects of wheat bread, wholemeal wheat bread and wholemeal rye bread on mechanisms which could have impact on chemoprevention were analysed in colon cells after in vitro fermentation.

METHODS

Effects of fermented bread samples on gene expression, glutathione S-transferase activity and glutathione content, differentiation, growth and apoptosis were investigated using the human colon adenoma cell line LT97. Additionally, apoptosis was studied in normal and tumour colon tissue by determination of caspase activities.

RESULTS

The expression of 76 genes (biotransformation, differentiation, apoptosis) was significantly upregulated (1.5-fold) in LT97 cells. The fermented bread samples were able to significantly increase glutathione S-transferase activity (1.8-fold) and glutathione content (1.4-fold) of the cells. Alkaline phosphatase activity as a marker of differentiation was also significantly enhanced (1.7-fold). The fermented bread samples significantly inhibited LT97 cell growth and increased the level of apoptotic cells (1.8-fold). Only marginal effects on apoptosis in tumour compared to normal tissue were observed.

CONCLUSIONS

This is the first study which presents chemopreventive effects of different breads after in vitro fermentation. In spite of differences in composition, the results were comparable between the bread types. Nevertheless, they indicate a potential involvement of this staple food product regarding the prevention of colon cancer.

Antiproliferative activity of melanoidins isolated from heated potato fiber (potex) in glioma cell culture model

Potex constitutes a potato fiber preparation widely used as an ingredient to meat and bakery products which thermal treatment results in creation of new compounds. Melanoidins are high molecular weight brown end products of Maillard reaction, and few data presenting tumor cell growth inhibiting activity of melanoidins have been reported. Thus, in present study we utilized water extract of Potex roasted (180 °C for 2 h), whose chemical characterization revealed the presence of melanoidin complexes. Heated Potex extract inhibited C6 glioma cell proliferation in a dose-dependent manner measured by MTT method. High molecular weight components present in initial extract were responsible for stronger antiproliferative effect compared with low molecular weight fraction. Impaired MAPK (mitogen-activated protein kinase) and Akt signaling was found in cells treated with the extract. Moreover, flow cytometry analyses revealed the extract to induce G1/S arrest in glioma cells. Simultaneously, Western blot analysis showed elevated levels of p21 protein with concomitant decrease of cyclin D1. In conclusion, observed antiproliferative activity of melanoidins present in heated Potex was linked to disregulated MAPK and Akt signaling pathways, as well as to cell cycle cessation. These results suggest potential application of Potex preparation as a functional food ingredient and chemopreventive agent.

Dietary fiber as a carrier of dietary antioxidants: an essential physiological function

The literature addresses dietary fiber (DF) and antioxidants (AOX) separately as nonrelated compounds. This paper proposes to show that DF and AOX could be approached jointly in nutrition and health studies because around 50% of the total dietary antioxidants, mainly polyphenolics, traverse the small intestine linked to dietary fiber. These antioxidants have received little attention so far. They release the fiber matrix in the colon by the action of the bacterial microbiota, producing metabolites and an antioxidant environment. The content of polyphenols associated with DF in different foods and their potential health-related properties, including animal experiments and human trials, are reviewed. It is concluded that the transportation of dietary antioxidants through the gastrointestinal tract may be an essential function of DF.

Effects of dietary fiber and its components on metabolic health

Dietary fiber and whole grains contain a unique blend of bioactive components including resistant starches, vitamins, minerals, phytochemicals and antioxidants. As a result, research regarding their potential health benefits has received considerable attention in the last several decades. Epidemiological and clinical studies demonstrate that intake of dietary fiber and whole grain is inversely related to obesity, type two diabetes, cancer and cardiovascular disease (CVD). Defining dietary fiber is a divergent process and is dependent on both nutrition and analytical concepts. The most common and accepted definition is based on nutritional physiology. Generally speaking, dietary fiber is the edible parts of plants, or similar carbohydrates, that are resistant to digestion and absorption in the small intestine. Dietary fiber can be separated into many different fractions. Recent research has begun to isolate these components and determine if increasing their levels in a diet is beneficial to human health. These fractions include arabinoxylan, inulin, pectin, bran, cellulose, β-glucan and resistant starch. The study of these components may give us a better understanding of how and why dietary fiber may decrease the risk for certain diseases. The mechanisms behind the reported effects of dietary fiber on metabolic health are not well established. It is speculated to be a result of changes in intestinal viscosity, nutrient absorption, rate of passage, production of short chain fatty acids and production of gut hormones. Given the inconsistencies reported between studies this review will examine the most up to date data concerning dietary fiber and its effects on metabolic health.

Mechanisms of primary cancer prevention by butyrate and other products formed during gut flora-mediated fermentation of dietary fibre

Dietary fibres are indigestible food ingredients that reach the colon and are then fermented by colonic bacteria, resulting mainly in the formation of short-chain fatty acids (SCFA) such as acetate, propionate, and butyrate. Those SCFA, especially butyrate, are recognised for their potential to act on secondary chemoprevention by slowing growth and activating apoptosis in colon cancer cells. Additionally, SCFA can also act on primary prevention by activation of different drug metabolising enzymes. This can reduce the burden of carcinogens and, therefore, decrease the number of mutations, reducing cancer risk. Activation of GSTs by butyrate has been studied on mRNA, protein, and enzyme activity level by real-time RT-PCR, cDNA microarrays, Western blotting, or photometrical approaches, respectively. Butyrate had differential effects in colon cells of different stages of cancer development. In HT29 tumour cells, e.g., mRNA GSTA4, GSTP1, GSTM2, and GSTT2 were induced. In LT97 adenoma cells, GSTM3, GSTT2, and MGST3 were induced, whereas GSTA2, GSTT2, and catalase (CAT) were elevated in primary colon cells. Colon cells of different stages of carcinogenesis differed in post-transcriptional regulatory mechanisms because butyrate increased protein levels of different GST isoforms and total GST enzyme activity in HT29 cells, whereas in LT97 cells, GST protein levels and activity were slightly reduced. Because butyrate increased histone acetylation and phosphorylation of ERK in HT29 cells, inhibition of histone deacetylases and the influence on MAPK signalling are possible mechanisms of GST activation by butyrate. Functional consequences of this activation include a reduction of DNA damage caused by carcinogens like hydrogen peroxide or 4-hydroxynonenal (HNE) in butyrate-treated colon cells. Treatment of colon cells with the supernatant from an in vitro fermentation of inulin increased GST activity and decreased HNE-induced DNA damage in HT29 cells. Additional animal and human studies are needed to define the exact role of dietary fibre and butyrate in inducing GST activity and reducing the risk of colon cancer.

Diet and epigenetics in colon cancer

Over the past few years, evidence has accumulated indicating that apart from genetic alterations, epigenetic alterations, through e.g. aberrant promoter methylation, play a major role in the initiation and progression of colorectal cancer (CRC). Even in the hereditary colon cancer syndromes, in which the susceptibility is inherited dominantly, cancer develops only as the result of the progressive accumulation of genetic and epigenetic alterations. Diet can both prevent and induce colon carcinogenesis, for instance, through epigenetic changes, which regulate the homeostasis of the intestinal mucosa. Food-derived compounds are constantly present in the intestine and may shift cellular balance toward harmful outcomes, such as increased susceptibility to mutations. There is strong evidence that a major component of cancer risk may involve epigenetic changes in normal cells that increase the probability of cancer after genetic mutation. The recognition of epigenetic changes as a driving force in colorectal neoplasia would open new areas of research in disease epidemiology, risk assessment, and treatment, especially in mutation carriers who already have an inherited predisposition to cancer.

Assessment of DNA damage and its modulation by dietary and genetic factors in smokers using the Comet assay: a biomarker model

Methods are needed to assess exposure to genotoxins in humans and to improve understanding of dietary cancer prevention. The Comet assay was used to detect smoking-related exposures and dietary modulations in target tissues. Buccal scrapings, blood and faeces were collected from 38 healthy male volunteers (smokers and non-smokers) during a dietary intervention study with bread supplemented with prebiotics+/-antioxidants. GSTM1-genotype was determined with PCR. Buccal and peripheral lymphocytes were analysed for DNA damage using the Comet assay. Genotoxicity of faecal water (FW) was assayed in human colon HT29 clone 19A cells. 'Tail intensity' (TI) was used as a quantitative indicator of DNA damage in the Comet assay. Intervention with bread reduced DNA damage in lymphocytes of smokers (8.3+/-1.7% TI versus 10.2+/-4.1% TI, n=19), but not of non-smokers (8.6+/-2.8% TI versus 8.3+/-2.7% TI, n=15). Faecal water genotoxicity was reduced only in non-smokers (9.4+/-2.9% TI versus 18.9+/-13.1% TI, n=15) but not in smokers (15.5+/-10.7% TI versus 20.4+/-14.1% TI, n=13). The Comet assay was efficient in the detection of both smoking-related exposure (buccal cells) and efficacy of dietary intervention (faecal samples). Smokers and non-smokers profited differently from the intervention with prebiotic bread+/-antioxidants. Stratification of data by genotype enhanced specificity/sensitivity of the intervention effects and contributed important information on the role of susceptibility.

Effect of apple cell walls and their extracts on the activity of dietary antioxidants

The effect of dietary fiber in the form of apple cell walls and pectin extracts on natural antioxidants was examined. Cell walls (CW), isolated from apples ( Malus domestica Borkh. cv. "Pacific Rose"), were incubated with ascorbic acid (AA) or quercetin in N-2-hydroxyethylpiperazine- N'-2-ethanesulfonic acid (HEPES) buffer (pH 6.5) at 37 degrees C for 2 h. The resulting supernatants were characterized by a ferric reducing antioxidant power (FRAP) assay and cyclic voltammetry (CV). The experiments were repeated with pectin isolated from the apple cell walls and commercial pectins and showed that polysaccharide preparations stabilized AA effectively but offered little protection against quercetin oxidation. The water-soluble components from cell walls appeared to be responsible for the observed effects of cell-wall polysaccharide preparations on antioxidant activity.

Cereal fiber intake may reduce risk of gastric adenocarcinomas: The EPIC-EURGAST study

Numerous case-control studies suggest dietary fiber may reduce risk of gastric cancer, but this has not been confirmed prospectively. A previous case-control study reported reduced risk of gastric cardia adenocarcinomas associated with cereal fiber, but not with fruit or vegetable fiber. To date, different food sources of fiber have not been examined with respect to noncardia tumors or diverse histologic sub-types. This study prospectively examines associations between fiber from different food sources and incident gastric adenocarcinomas (GC) among more than 435,000 subjects from 10 countries participating in the European Prospective Investigation into Cancer and Nutrition study. Subjects aged 25-70 years completed dietary questionnaires in 1992-98, and were followed up for a median of 6.7 years. About 312 incident GCs were observed. The relative risk of GC was estimated based on cohort-wide sex-specific fiber intake quartiles using proportional hazards models to estimate hazards ratios (HRs) and 95% confidence intervals (CIs). Intakes of cereal fiber, but not total, fruit or vegetable fiber, were associated with reduced GC risk [adjusted HR for the highest vs. lowest quartile of cereal fiber 0.69, 0.48-0.99]. There was a strong inverse association for diffuse [HR 0.43, 0.22-0.86], but not intestinal type [HR 0.98, 0.54-1.80] tumors. Associations for cardia vs. noncardia tumors were similar to those for overall GC, although cardia associations did not reach significance. Cereal fiber consumption may help to reduce risk of GC, particularly diffuse type tumors. Further study on different food sources of fiber in relation to GC risk is warranted to confirm these relationships.

Inulin-type fructans and reduction in colon cancer risk: review of experimental and human data

Inulin-type fructans (beta(2,1)fructans) extracted from chicory roots (Cichorium intybus) are prebiotic food ingredients, which in the gut lumen are fermented to lactic acid and SCFA. Research in experimental animal models revealed that inulin-type fructans have anticarcinogenic properties. A number of studies report the effects of inulin-type fructans on chemically induced pre-neoplastic lesions (ACF) or tumours in the colon of rats and mice. In twelve studies, there were twenty-nine individual treatment groups of which twenty-four measured aberrant crypt foci (ACF) and five measured tumours. There was a significant reduction of ACF in twenty-one of the twenty-four treatment groups and of tumour incidence in five of the five treatment groups. Higher beneficial effects were achieved by synbiotics (mixtures of probiotics and prebiotics), long-chain inulin-type fructans compared to short-chain derivatives, and feeding high-fat Western style diets. Inulin-type fructans reduced tumour incidence in APC(Min) mice in two of four studies and reduced growth and metastasising properties of implanted tumour cells in mice (four studies). The effects have been reported to be associated with gut flora-mediated fermentation and production of butyrate. In human cells, inulin-derived fermentation products inhibited cell growth, modulated differentiation and reduced metastasis activities. In conclusion, evidence has been accumulated that shows that inulin-type fructans and corresponding fermentation products reduced the risks for colon cancer. The involved mechanisms included the reduction of exposure to risk factors and suppression of tumour cell survival. Thus, this specific type of dietary fibre exerted both blocking agent and suppressing agent types of chemopreventive activities.

Dietary fibre and colorectal cancer: A model for environment - gene interactions

As environmental factors are clearly associated with risk for colorectal cancer, we set out to model how dietary fibre, or the effects of its ingestion, might impact upon the complex events that characterise colorectal oncogenesis. The diverse nature of dietary fibre and its resultant fate in the gut is outlined. The evidence indicates that different types of fibre create different conditions in different regions of the gut. This is reflected in different effects on oncogenesis especially in animal models. Data from animal models show that insoluble fibre is protective. Evidence from human studies are not consistent, especially considering the interventional studies. However, all such studies have been dependent on biomarkers short of cancer formation, for measurement of an effect. The biological and molecular events characteristic of colorectal oncogenesis are reviewed in an effort to identify how fibre ingestion might regulate oncogenesis. While several mechanisms might account for protection, the results of fermentation and especially butyrate production provide examples of how genomic instability might be controlled. Activation of apoptosis and cell cycle arrest seem likely to be mechanisms that would enable correction of genomic events that drive oncogenesis. Butyrate itself can regulate gene expression by both epigenetic and direct effects.

Dietary fiber as a versatile food component: An industrial perspective

The continued emphasis on the importance of dietary fibers to the Western diet and the need for products with a lower calorific content is pressuring food companies to allocate more resources to the development of fiber-enriched products. The challenge to the industry is to accomplish this goal without sacrificing the organoleptic appeal of some of their core offerings. As future research details specific nutritional benefits of individual components of dietary fiber, food companies will need flexible alternatives in order to validate new 'functional' food claims and to respond rapidly to emerging trends in fiber-enriched products. These objectives will be achieved by understanding the physicochemical basis for the biotechnical functionality of fibers and by developing, and making available fibers which provide a broad spectrum of bioactive and texture modulating properties.

Production and characterisation of two wheat-bran fractions: an aleurone-rich and a pericarp-rich fraction

Wheat bran is a good source of dietary fibre in the form of cell walls, but contains a number of different cell types. We describe a large-scale procedure for the production of an aleurone-rich and a pericarp-rich fraction from hard, Australian wheat. The fractions were characterised by field-emission scanning electron microscopy, by using a range of bright-field stains, colour reagents, and fluorochromes, and by chemical analysis of the walls. The aleurone fraction included the seed coat with its cuticle. Only the pericarp walls showed a histochemical reaction for lignin. The concentrations of ester-linked ferulic acid and (1-->3),(1-->4)-beta-glucans were greater in the aleurone-rich fraction than in the pericarp-rich fraction. The results are consistent with the arabinoxylans in the walls of the pericarp-rich fraction being more highly substituted with arabinose than those in the walls of the aleurone-rich fraction. When the fractions were fed as a dietary supplement to rats and walls were isolated from the faeces, it was found that the pericarp walls were not degraded, but the aleurone walls were partially degraded.

Diet and cancer prevention

Dietary effects are presumed to underlie many of the large international differences in incidence seen for most cancers. Apart from alcohol and a few micronutrients, however, the role of specific nutritional factors remains ill-defined. The evidence for a role of energy balance, physical inactivity, and obesity has strengthened, while for dietary fat it has weakened. Phytochemicals such as folate, lycopene and flavonoids are still the subject of active research. As the mechanisms underlying human carcinogenesis are better understood, dietary research will focus increasingly on intermediate markers such as the insulin-like growth factors and potentially carcinogenic metabolites.

Ballaststoffe: Mehr als ein Diätmittel

A nutrition rich in fibre has a preventive effect against constipation, colon diverticulosis, carcinoma of the large bowel and stomach, type 2-diabetes, metabolic syndrome and cardiovascular disease. In case of constipation, diverticulosis and diabetes this effect solely depends on dietary fibre. Regarding carcinomas and cardiovascular diseases, so far unknown factors integrated in or associated with fibre-rich food may also contribute to the preventive effect. Therapy with dietary fibre is indicated for constipation, colon diverticulosis, diarrhea, diabetes, and hypercholesterinemia. The individual dietary fibres differ substance-specifically. Food-integrated dietary fibre such as whole-grain bread, vegetables and fruit have their place in prevention. Dietary fibre preparations such as wheat bran, flax seed or sugar-beet fibre are useful in the treatment of constipation, colon diverticulosis and adiposity. Oat bran is preferentially used in hypercholesterinemia. Purified dietary fibres such as cellulose, guar, psyllium, and beta-glucan have an anti-diabetic, all viscous fibres an anti-lipaemic effect. The therapeutic dosages of dietary fibre preparations are 20-40 g/day and of purified fibres substances 10-20 g/day respectively.

Ballaststoffe: Mehr als ein Diätmittel

Dietary fibre is a heterogeneous group of substances which have only one common characteristic: the non-digestability in the small bowel. With one exception all fibres are carbohydrates (poly- or disaccharides). Some fibres are water-soluble, others are unsoluble. This property is associated with physiological effects. Soluble (viscous) fibres can bind water and thus form hydrocolloids or gels, unsoluble ones cannot. Dietary fibres play an essential role in the physiology of the gastrointestinal tract. They modify the absorption of nutrients (particularly carbohydrates and lipids) in the small bowel. They accelerate the gut transit time and determine stool composition and quantity. They are the main nutritional source for the colonic microflora. During the bacterial fermentation short-chain fatty acids are formed which are essential for nutrition and integrity of the colonocytes and for colonic function. Moreover gases, detoxicating enzymes, antioxidants and carcinogen-inactivating compounds arise. The most important fibres are cellulose, hemicellulose, pectin, guar, psyllium, beta-glucan, Klason lignin and digestion-resistant starch; they are present in varying amounts in plant foods and in fibre preparations. The usual daily intake of dietary fibre in Europe and the USA amounts to only 15-20 g, while health authorities and nutrition societies recommend a reference value of at least 30 g. Dietary fibres are applied as food-integrated, as supplement and as purified substances.

Dietary cancer and prevention using antimutagens

Many of the cancers common in the Western world, including colon, prostate and breast cancers, are thought to relate to dietary habits. Of the known risk factors, many will act through increasing the probability of mutation. Recognised dietary mutagens include cooked meat compounds, N-nitroso compounds and fungal toxins, while high meat and saturated fat consumption, increasing rates of obesity, and regular consumption of alcohol and tobacco are all dietary trends that could indirectly enhance the probability of mutation. However, there are significant difficulties in implementing and sustaining major dietary changes necessary to reduce the population's intake of dietary mutagens. Dietary antimutagens may provide a means of slowing progression toward cancer, and be more acceptable to the population. Consideration of genetic mechanisms in cancer development suggest several distinct targets for intervention. Strategies that reduce mutagen uptake may be the most simple intervention, and the one least likely to result in undesirable side effects. Certain (but not all) types of dietary fibres appear to reduce mutation through this mechanism, as may certain probiotics and large planar molecules such as chlorophyllin. Antioxidants have been suggested to scavenge free radicals, and prevent their interactions with cellular DNA. Small molecule dietary antioxidants include ascorbic acid, Vitamin E, glutathione, various polyphenols and carotenoids. We found a statistically significant relationship between colon cancer incidence and soil selenium status across different regions of New Zealand. Additionally, a study of middle-aged men suggested that blood selenium levels lower than 100 ng/ml were inadequate for repair or surveillance of oxidative (and other) DNA damage. We suggest that selenium will be an important antimutagen, at least in New Zealand, possibly through antioxidant effects associated with selenium's role in enzymes associated with endogenous repair of DNA damage. Modulation of xenobiotic metabolizing enzymes is well recognised as cancer-protective, and is a property of various flavonoids and a number of sulfur-containing compounds. Many fruits and vegetables contain compounds that will protect against mutation and cancer by several mechanisms. For example, kiwifruit has antioxidant effects and may also affect DNA repair enzymes. Dietary folate may be a key factor in maintenance of methylation status, while enhanced overall levels of vitamins and minerals may retard the development of genomic instability. The combination of each of these factors could provide a sustainable intervention that might usefully delay the development of cancer in New Zealand and other populations. Although there are a range of potentially antimutagenic fruits, vegetables and cereals available to these populations, current intake is generally below the level necessary to protect from dietary or endogenous mutagens. Dietary supplementation may provide an alternative approach.

Plant foods, fiber, and rectal cancer

BACKGROUND

Associations between colon and rectal cancer and intakes of vegetables, other plant foods, and fiber have stimulated much debate.

OBJECTIVE

We examined the association between rectal cancer and plant food and fiber intakes.

DESIGN

Data from 952 incident cases of rectal cancer were compared with data from 1205 population-based controls living in Utah or enrolled in the Kaiser Permanente Medical Care Program in northern California

RESULTS

Rectal cancer was inversely associated with intakes of vegetables (odds ratio: 0.72; 95% CI: 0.54, 0.98), fruit (0.73; 0.53, 0.99), and whole-grain products (0.69; 0.51, 0.94), whereas a high intake of refined-grain products was directly associated with an increased risk of rectal cancer (1.42; 1.04, 1.92). Similarly, relative to low fiber intakes, high intakes of dietary fiber reduced the risk of rectal cancer (0.54; 0.37, 0.78). The reduced risk of rectal cancer associated with vegetable (0.48; 0.29, 0.80), fruit (0.63; 0.38, 1.06), and fiber (0.40; 0.22, 0.71) intakes was strongest for persons who received the diagnosis after age 65 y. A threshold effect at approximately 5 servings of vegetables/d was needed to see a reduced risk of rectal cancer.

CONCLUSIONS

The results suggest that plant foods may be important in the etiology of rectal cancer in both men and women. Age at diagnosis appears to play an important role in the association.

Butyrate is only one of several growth inhibitors produced during gut flora-mediated fermentation of dietary fibre sources

Dietary fibre sources are fermented by the gut flora to yield short-chain fatty acids (SCFA) together with degraded phytochemicals and plant nutrients. Butyrate, a major SCFA, is potentially chemoprotective by suppressing the growth of tumour cells and enhancing their differentiation. Conversely, it could lead to a positive selection pressure for transformed cells by inducing glutathione S-transferases (GST) and enhancing chemoresistance. Virtually nothing is known about how butyrate's activities are affected by other fermentation products. To investigate such interactions, a variety of dietary fibre sources was fermented with human faecal slurries in vitro, analysed for SCFA, and corresponding SCFA mixtures were prepared. HT29 colon tumour cells were treated for 72 h with individual SCFA or complex samples. The growth of cells, GST activity, and chemoresistance towards 4-hydroxynonenal were determined. Fermentation products inhibited cell growth more than the corresponding SCFA mixtures, and the SCFA mixtures were more active than butyrate, probably due to phytoprotectants and to propionate, respectively, which also inhibit cell growth. Only butyrate induced GST, whereas chemoresistance was caused by selected SCFA mixtures, but not by all corresponding fermentation samples. In summary, fermentation supernatant fractions contain compounds that: (1) enhance the anti-proliferative properties of butyrate (propionate, phytochemical fraction); (2) do not alter its capacity to induce GST; (3) prevent chemoresistance in tumour cells. It can be concluded that fermented dietary fibre sources are more potent inhibitors of tumour cell growth than butyrate alone, and also contain ingredients which counteract the undesired positive selection pressures that higher concentrations of butyrate induce in tumour cells.

Effect of diet, life style, and other environmental/chemopreventive factors on colorectal cancer development, and assessment of the risks

This review presents a comprehensive, evenhanded evaluation of the evidence from experimental, in vitro and human studies associating environmental and therapeutic factors with risk of colorectal cancer. Life styles correlated with the greatest increase in colorectal cancer risk are the ones that typify a diet rich in fat and calories, alcohol drinking and tobacco smoking, and low intake of vegetable, fruits and fibers, referred to as a "western diet," as well as sedentary style (i.e., no- or low-exercise). This kind of life style has also been associated with other chronic diseases (other cancers, obesity, dyslipedemia, diabetes, hypertension cardiovascular, and hypertension). The evidence does not implicated red meat as a risk factor, and fiber has been shown to protect against colorectal adenomas and carcinomas. Calcium, vitamin D, folate, and some antioxidant vitamins and minerals (gamma-tocopherol and selenium) have protective effects, and daily exercise for > or =30 min results in a significant decrease in risk. Estrogen use (hormone replacement therapy) substantially reduces colorectal cancer risk in postmenopausal women. Nonsteroidal anti-inflammatory drugs (e.g., aspirin) in excessive doses is protective, especially in high risk populations, but the side effects of its use and cost incurred due to its continued intake over long periods must be carefully scrutinized before any recommendations are made for the general public.

Plasma enterolactone or intestinal Bifidobacterium levels do not explain adenoma formation in multiple intestinal neoplasia (Min) mice fed with two different types of rye-bran fractions

The study was designed to evaluate whether two types of rye-bran fractions result in distinct bifidogenic effect or enterolactone production in multiple intestinal neoplasia (Min) mice and whether these parameters are associated with intestinal tumorigenesis in this animal model. The experimental diets were a non-fibre diet (control), a rye-bran diet, and diets containing either the soluble extract or the insoluble fraction prepared from rye bran. The main result on adenoma formation in these experiments was the observation that the soluble extract increased number (P=0.012) and size (P=0.008) of adenomas in the distal small intestine when compared with the non-fibre group. All rye-supplemented diets supported similarly the in vivo growth of Bifidobacterium (10(8)-10(9) colony forming units/g) in Min mice, whereas the non-fibre diet lowered intestinal Bifidobacterium below the level of detection. The results show that water solubility does not affect the bifidogenicity of rye bran. Mean plasma enterolactone concentration was highest in the rye-bran group (30.0 nmol/l; P=0.002), which along with the soluble-extract group (16.2 nmol/l; P=0.024) differed significantly from the non-fibre diet group (7.5 nmol/l). Thus, the mice fed with the rye bran were the best enterolactone producers. In conclusion, rye bran and rye fractions influence adenoma formation in Min mice to a varying degree but plasma enterolactone levels or the production of bifidogenic bacteria do not mediate the effect.