Fibre and effects on probiotics (the prebiotic concept)

The burden (economic and medicinal) of acute and chronic gut disorders continues to increase. As efficient therapies are few, attention has turned towards the use of so-called functional foods to mediate against gut disorder. These target particular genera of gut bacteria seen as beneficial, e.g. bifidobacteria, lactobacilli. The use of products containing live microbial species (probiotics) has a long history of use in humans and many trials have been reported as 'positive'. Taking the view that positive components of the gut flora already exist in the intestinal tract, the prebiotic concept has been developed. Here, dietary carbohydrates have a selective metabolism within the gut flora thereby shifting the community towards a more advantageous structure. Conventional fibres like pectins, cellulose, etc. are not selectively metabolised by gut bacteria. However, certain oligosaccharides do have this capability. Most research has been conducted with fructooligosaccharides, like inulin, which have a powerful bifidogenic effect. Trials are ongoing to determine the clinical benefits of prebiotic use. Intestinal disorders like ulcerative colitis, gastroenteritis and irritable bowel syndrome are particular targets. (c) 2004 Elsevier Ltd. All rights reserved.

From probiotics to prebiotics and a healthy digestive system

Ingestion of probiotics can be recommended as a preventative approach to maintaining intestinal microflora balance and thereby enhance 'well-being'. Undoubtedly, probiotic bacteria will vary in their efficacy. The literature indicates positive results in over 50 human trials with prevention/treatment of infections the most frequently reported. In theory increased levels of probiotics may induce a 'barrier' influence against common pathogens. Mechanisms of effect are likely to include the excretion of acids (lactate, acetate), competition for nutrients and gut receptor sites, immuno-modulation and the formation of specific antimicrobial agents. An alternative, or additional, approach is the prebiotic concept. This takes the view that probiotics are present indigenous to the gut and that a rational approach towards increasing their numbers would be to consume food ingredients (carbohydrates) that have a selective metabolism in the lower gut. A prebiotic is 'a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon that can improve the host health.' In particular, the ingestion of fructo-oligosaccharides, galacto-oligosaccharides, and lactulose has shown to stimulate bifidobacteria in the lower gut.

In vitro study on gas generation and prebiotic effects of some carbohydrates and their mixtures

This study was carried out to examine the effect or inulin (IN), fructooligosaccharide (FOS), polydextrose (POL) and isomaltooligosaccharides (ISO), alone and in combination, on gas production, gas composition and prebiotic effects. Static batch culture fermentation was performed with faecal samples from three healthy volunteers to study the volume and composition of gas generated and changes in bacterial populations. Four carbohydrates alone or mixed with one another (50:50) were examined. Prebiotic index (PI) was calculated and used to compare the prebiotic effect. The high amount of gas produced by IN was reduced by mixing it with FOS. No reduction in gas generation was observed when POL and ISO mixed with other substrates. It was found that the mixture of IN and FOS was effective in reducing the amount of gas produced while augmenting or maintaining their potential to Support the growth of bifidobacteria in Faecal batch culture as the highest PI was achieved with FOS alone and a mixture of FOS and IN. It was also found that high volume of gas was generated in presence of POL and ISO and they had lower prebiotic effect. The results of this study imply that a Mixture of prebiotics could prove effective in reducing the amount of gas generated by the gut microflora. (c) 2007 Elsevier Ltd. All rights reserved.

Cetobacterium somerae sp nov from human feces and emended description of the genus Cetobacterium

Phenotypic and phylogenetic studies were performed on four isolates of an unidentified gram-negative, microaerotolerant, non-spore-forming, rod-shaped bacterium isolated from the feces of children. The unknown organism was bile resistant and produced acetic acid as the major end product of metabolism of peptides and carbohydrates. It possessed a low DNA G + C content of 31 mol %. Comparative 16S rRNA gene sequencing demonstrated that the four isolates were phylogenetically identical (100% 16S rRNA sequence similarity) and represent a hitherto unknown sub-line within the genus Cetobacterium. The novel bacterium displayed approximately 5% sequence divergence with Cetobacterium ceti, and can be readily distinguished from the latter by physiological and biochemical criteria. Based on phylogenetic and phenotypic evidence, it is proposed that the unknown fecal bacterium be classified in the genus Cetobacterium, as Cetobacterium somerae sp. nov. The proposed type strain of Cetobacterium somerae is WAL 14325(T) (ATCC BAA-474(T) = CCUG 46254T).

The gut microbiota and lipid metabolism: implications for human health and coronary heart disease

Coronary heart disease (CHD) is the leading cause of mortality in Western societies, affecting about one third of the population before their seventieth year. Over the past decades modifiable risk factors of CHD have been identified, including smoking and diet. These factors when altered can have a significant impact on an individuals' risk of developing CHD, their overall health and quality of life. There is strong evidence suggesting that dietary intake of plant foods rich in fibre and polyphenolic compounds, effectively lowers the risk of developing CHD. However, the efficacy of these foods often appears to be greater than the sum of their recognised biologically active parts. Here we discuss the hypothesis that beneficial metabolic and vascular effects of dietary fibre and plant polyphenols are due to an up regulation of the colon-systemic metabolic axis by these compounds. Fibres and many polyphenols are converted into biologically active compounds by the colonic microbiota. This microbiota imparts great metabolic versatility and dynamism, with many of their reductive or hydrolytic activities appearing complementary to oxidative or conjugative human metabolism. Understanding these microbial activities is central to determining the role of different dietary components in preventing or beneficially impacting on the impaired lipid metabolism and vascular dysfunction that typifies CHD and type 11 diabetes. This approach lays the foundation for rational selection of health promoting foods, rational target driven design of functional foods, and provides an essential thus-far, overlooked, dynamic to our understanding of how foods recognised as "healthy" impact on the human metabonome.

Extra virgin olive oil phenolics: absorption, metabolism, and biological activities in the GI tract

Olive oil, a typical ingredient of the Mediterranean diet, possesses many beneficial health effects. The biological activities ascribed to olive oil consumption are associated in part to its phenolics constituents, and mainly linked to the direct or indirect antioxidant activity of olive oil phenolics and their metabolites, which are exerted more efficiently in the gastrointestinal (GI) tract, where dietary phenolics are more concentrated when compared to other organs. In this regard, we present a brief overview of the metabolism, biological activities, and anticancer properties of olive oil phenolics in the GI tract. Toxicology and Industrial Health 2009; 25: 285-293.

alpha-tocopherol affects androgen metabolism in male rat

The Alpha-Tocopherol Beta-Carotene Cancer Prevention Study has provided the first evidence implicating vitamin E in hormone synthesis. The effect of vitamin E on stereoidogenesis in testes and adrenal glands was assessed in growing rats using Affymetrix gene-chip technology. Dietary supplementation of rats with vitamin E (60 mg/kg feed) for a period of 429 days caused a significant repression of genes encoding for proteins centrally involved in the uptake (low-density lipoprotein receptor) and de novo synthesis (for example, 7-dehydrocholesterol reductase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, isopentenyl-diphosphate delta-isomerase, and farnesyl pyrophosphate synthetase) of cholesterol, the precursor of all steroid hormones. The present investigation indicates that dietary vitamin E may induce changes in stereoidogenesis by affecting cholesterol homeostasis.

The impact of EPA and DHA on blood lipids and lipoprotein metabolism: influence of apoE genotype

Fish and fish oil-rich sources of long-chain n-3 fatty acids have been shown to be cardio-protective, through a multitude of different pathways including effects on arrythymias, endothelial function, inflammation and thrombosis, as well as modulation of both the fasting and postprandial blood lipid profile. To date the majority of studies have examined the impact of EPA and DHA fed simultaneously as fish or fish oil supplements. However, a number of recent studies have compared the relative biopotency of EPA v. DHA in relation to their effect on blood lipid levels. Although many beneficial effects of fish oils have been demonstrated, concern exists about the potential deleterious impact of EPA and DHA on LDL-cholesterol, with a highly-heterogenous response of this lipid fraction reported in the literature. Recent evidence suggests that apoE genotype may be in part responsible. In the present review the impact of EPA and DHA on cardiovascular risk and the blood lipoprotein profile will be considered, with a focus on the apoE gene locus as a possible determinant of lipid responsiveness to fish oil intervention.

Influence of birth weight on gene regulators of lipid metabolism and utilization in subcutaneous adipose tissue and skeletal muscle of neonatal pigs.

Epidemiological studies suggest that low-birth weight infants show poor neonatal growth and increased susceptibility to metabolic syndrome, in particular, obesity and diabetes. Adipose tissue development is regulated by many genes, including members of the peroxisome proliferator-activated receptor (PPAR) and the fatty acid-binding protein (FABP) families. The aim of this study was to determine the influence of birth weight on key adipose and skeletal muscle tissue regulating genes. Piglets from 11 litters were ranked according to birth weight and 3 from each litter assigned to small, normal, or large-birth weight groups. Tissue samples were collected on day 7 or 14. Plasma metabolite concentrations and the expression of PPARG2, PPARA, FABP3, and FABP4 genes were determined in subcutaneous adipose tissue and skeletal muscle. Adipocyte number and area were determined histologically. Expression of FABP3 and 4 was significantly reduced in small and large, compared with normal, piglets in adipose tissue on day 7 and in skeletal muscle on day 14. On day 7, PPARA and PPARG2 were significantly reduced in adipose tissue from small and large piglets. Adipose tissue from small piglets contained more adipocytes than normal or large piglets. Birth weight had no effect on adipose tissue and skeletal muscle lipid content. Low-birth weight is associated with tissue-specific and time-dependent effects on lipid-regulating genes as well as morphological changes in adipose tissue. It remains to be seen whether these developmental changes alter an individual's susceptibility to metabolic syndrome.

Effect of incremental levels of fish oil in the diet on ruminal lipid metabolism in growing steers

Based on the potential benefits to human health, there is interest in developing sustainable nutritional strategies to enhance the concentration of long-chain n-3 fatty acids in ruminant-derived foods. Four Aberdeen Angus steers fitted with rumen and duodenal cannulae were used in a 4 × 4 Latin square experiment with 21 d experimental periods to examine the potential of fish oil (FO) in the diet to enhance the supply of 20 : 5n-3 and 22 : 6n-3 available for absorption in growing cattle. Treatments consisted of total mixed rations based on maize silage fed at a rate of 85 g DM/kg live weight0·75/d containing 0, 8, 16 and 24 g FO/kg diet DM. Supplements of FO reduced linearly (P < 0·01) DM intake and shifted (P < 0·01) rumen fermentation towards propionate at the expense of acetate and butyrate. FO in the diet enhanced linearly (P < 0·05) the flow of trans-16 : 1, trans-18 : 1, trans-18 : 2, 20 : 5n-3 and 22 : 6n-3, and decreased linearly (P < 0·05) 18 : 0 and 18 : 3n-3 at the duodenum. Increases in the flow of trans-18 : 1 were isomer dependent and were determined primarily by higher amounts of trans-11 reaching the duodenum. In conclusion, FO alters ruminal lipid metabolism of growing cattle in a dose-dependent manner consistent with an inhibition of ruminal biohydrogenation, and enhances the amount of long-chain n-3 fatty acids at the duodenum, but the increases are marginal due to extensive biohydrogenation in the rumen.

The effect of dietary nitrate on salivary, plasma, and urinary nitrate metabolism in humans

Dietary nitrate is metabolized to nitrite by bacterial flora on the posterior surface of the tongue leading to increased salivary nitrite concentrations. In the acidic environment of the stomach, nitrite forms nitrous acid, a potent nitrating/nitrosating agent. The aim of this study was to examine the pharmacokinetics of dietary nitrate in relation to the formation of salivary, plasma, and urinary nitrite and nitrate in healthy subjects. A secondary aim was to determine whether dietary nitrate increases the formation of protein-bound 3-nitrotyrosine in plasma, and if dietary nitrate improves platelet function. The pharmacokinetic profile of urinary nitrate excretion indicates total clearance of consumed nitrate in a 24 h period. While urinary, salivary, and plasma nitrate concentrations increased between 4- and 7-fold, a significant increase in nitrite was only detected in saliva (7-fold). High dietary nitrate consumption does not cause a significant acute change in plasma concentrations of 3-nitrotyrosine or in platelet function.

Metabolism of tea flavonoids in the gastrointestinal tract

There is considerable interest in the bioavailability of flavan-3-ols such as tea catechins and their bioactivity in vivo. Although flavanols such as catechin and epicatechin have long been characterized as powerful antioxidants in vitro, evidence suggests that these compounds undergo significant metabolism and conjugation during absorption in the small intestine and in the colon. In the small intestine these modifications lead primarily to the formation of glucuronide conjugates that are more polar than the parent flavanol and are marked for renal excretion. Other phase II processes lead to the production of O-methylated forms that have reduced antioxidant potential via the methylation of the B-ring catechol. Significant modification of flavanols also occurs in the colon where the resident microflora degrade them to smaller phenolic acids, some of which may be absorbed. Cell, animal and human studies have confirmed such metabolism by the detection of flavanol metabolites in the circulation and tissues. This review will highlight the major sites of flavanol metabolism in the gastrointestinal tract and the processes that give rise to potential bioactive forms of flavan-3-ols in vivo.