RS and Gut Microbe Studies

The internet has been a game-changer in terms of what information is available to the layperson. With a bit of computer savvy, not only can you find new and exciting information, but you can track trends and watch the latest science as it’s happening.

With subjects like gut microbes or resistant starch you rarely see, hear, or read about anything other than maybe a segment on an afternoon health show or an article in a fitness magazine—it’s tough to know what to believe.  But with just a few clicks of the mouse, you can be immersed in scientific literature so deep it will make your head spin.  Much of our research in the early days of the internet was through labored searches with many dead-ends more often than not taking you quickly towards someone with something to sell, or to images so (porno) graphic you were changed forever.  After a few years, we got a little smarter on how to search for information, where the best information is kept, and what to expect.  I am now going to share what I’ve learned with you.

When it comes to health and science, three sources stand out for accessing information
:

http://www.ncbi.nlm.nih.gov/pubmed/  PubMed is a free search engine accessing different databases and has more than 23 million entries for medical and life science studies, journals, and books. The United States National Library of Medicine (NLM) at the National Institutes of Health maintains the database.

http://journals.cambridge.org/action/search  The Cambridge Journals are maintained by the Cambridge University in England to advance learning, knowledge and research worldwide, the Press currently publishes over 300 peer-reviewed academic journals for the global market. Containing the latest research from a broad sweep of subject areas, Cambridge journals are accessible worldwide in print and online.

http://scholar.google.com/  Google Scholar is a freely accessible web search engine that indexes the full text of scholarly literature across an array of publishing formats and disciplines. Released in November 2004, the Google Scholar index includes most peer-reviewed online journals of Europe and America's largest scholarly publishers, plus scholarly books and other non-peer reviewed journals.

Searching for information with these three search engines is a breeze.  They are all very user-friendly and allow advanced searches letting you look for a favorite author, a string of words, or only studies within a certain date range.

GUT BUG AND RESISTANT STARCH STUDIES

Without exception, when I start talking about gut bugs and resistant starch, people say something like, “Why am I just now hearing about this?”  Everyone has heard of prebiotics, probiotics, and every dieting strategy under the sun.  But gut bugs and especially RS?  “Never heard of ‘em.”

I wanted to devote an entire blog post to the latest studies on gut bugs and RS.  I could have easily done the same with any of the other concepts I enjoy talking about so much, but the topic always comes back around to these two intertwined subjects.  With these few tools, and knowing what to look for, you’ll be able to easily search for anything you like, no longer do you need to rely on TV doctors for your medical knowledge, you can get it straight from the horse’s mouth.
  

Here you’ll see what I came up with by searching PubMed, Cambridge Journals, and Google Scholar for the terms “resistant starch” or a combination of words to pull up latest research into the human microbiome. If you want more information on any of these papers, simply put the PubMed ID number (PMID) in any search engine and hit “GO.” For entries without a PMID, you can just copy the entire name of the study and search using only that. You’ll notice that it is very easy to get an “abstract” or a brief description of a study.

Oftentimes the full-text of the study will be available, but more likely you will be asked to pay before you can see the complete study.  Getting full access to all these studies is just a few dollars and a few mouse clicks away, but if you are tight with your money, a wealth of information can be had for free just by reading the abstracts and by finding free full-text studies.

RESISTANT STARCH STUDIES

The subject of resistant starch is absolutely fascinating.  You can actually witness in real-time the mind-blowing scrutiny that this one simple food source is receiving.  It’s not the latest ‘superfood’ or ‘one weird little trick,’ but a truly remarkable source of food that can selectively feed the most beneficial gut bugs in our colon and create huge metabolic changes.

Resistant starch was identified and talked about as far back as 1922, many years before its importance was realized.  The near linear rise in studies on RS should tell you that this is the stock to buy—it’s gettin’ good!

New entries for the phrase “resistant starch” by year:

	PubMed	Cambridge Journals	Google Scholar
2004	74	134	500
2005	68	127	661
2006	66	150	784
2007	82	170	913
2008	91	151	1060
2009	92	182	1200
2010	96	263	1410
2011	102	318	1509
2012	136	199	1610
2013	148	261	2020
2014 (as of 20 Oct)	118	168	1710

   

GUT MICROBE STUDIES

Searching for studies on gut bugs is a bit more difficult.  There are so many terms used (ie. gut microbes, intestinal microbiome, human gut commensals, etc…) that it is difficult to narrow down your search.  Here is a table of studies and papers, focusing on human health, and containing the exact phrase “human gut microbiome” in the years indicated:

	PubMed	Cambridge Journals	Google Scholar
2004	28	22	2
2005	39	19	3
2006	69	25	11
2007	86	19	23
2008	152	24	36
2009	190	15	99
2010	353	39	187
2011	452	28	490
2012	653	17	742
2013	855	28	1320
2014 (as of 20 Oct)	692	42	1270

Again, as with resistant starch, you can see the interest in the subject of what drives our “second-brain” is not waning.  As newer test methods are developed to examine the intricacies of our guts, more and more studies are performed to examine the effects and ramifications of manipulating the human gut microbiome.

The Abstract

When you start digging into the world of scientific papers, you’ll soon learn that you can easily uncover abstracts for free.  Abstracts are an overview of the entire paper and usually end with a conclusion or summary, they are very useful for getting a general impression of what’s in the paper, but often you’ll need to pay if you want to see the entire study.  Oftentimes a free “full text” paper is offered. The remainder of this blog post is a collection of 24 abstracts (from 2013 through 2014) discussing the interaction of resistant starch and the gut microbiome.  If a free “full text” is available, it will be noted as “Free PMC Article.”

Please, if anyone wants to discuss any of these in-depth, I'll see if I can get the full-text and I'll do some follow-on blog posts to dissect the studies you find interesting.

2014 Papers:

1. Pilot study of diet and microbiota: interactive associations of fibers and polyphenols with human intestinal bacteria.

Several studies have addressed the use of dietary fibers in the modulation of intestinal microbiota; however, information about other highly correlated components in foods, such as polyphenols, is scarce. The aim of this work was to explore the association between the intake of fibers and polyphenols from a regular diet and fecal microbiota composition in 38 healthy adults. Food intake was recorded using an annual food frequency questionnaire (FFQ). Quantification of microbial populations in feces was performed by quantitative PCR. A negative association was found between the intake of pectins and flavanones from oranges and the levels of Blautia coccoides and Clostridium leptum. By contrast, white bread, providing hemicellulose and resistant starch, was directly associated with Lactobacillus. Because some effects on intestinal microbiota attributed to isolated fibers or polyphenols might be modified by other components present in the same food, future research should be focused on diet rather than individual compounds.

PMID: 24877654

2. Impact of diet and individual variation on intestinal microbiota composition and fermentation products in obese men.

There is growing interest in understanding how diet affects the intestinal microbiota, including its possible associations with systemic diseases such as metabolic syndrome. Here we report a comprehensive and deep microbiota analysis of 14 obese males consuming fully controlled diets supplemented with resistant starch (RS) or non-starch polysaccharides (NSPs) and a weight-loss (WL) diet. We analyzed the composition, diversity and dynamics of the fecal microbiota on each dietary regime by phylogenetic microarray and quantitative PCR (qPCR) analysis. In addition, we analyzed fecal short chain fatty acids (SCFAs) as a proxy of colonic fermentation, and indices of insulin sensitivity from blood samples. The diet explained around 10% of the total variance in microbiota composition, which was substantially less than the inter-individual variance. Yet, each of the study diets induced clear and distinct changes in the microbiota. Multiple Ruminococcaceae phylotypes increased on the RS diet, whereas mostly Lachnospiraceae phylotypes increased on the NSP diet. Bifidobacteria decreased significantly on the WL diet. The RS diet decreased the diversity of the microbiota significantly. The total 16S ribosomal RNA gene signal estimated by qPCR correlated positively with the three major SCFAs, while the amount of propionate specifically correlated with the Bacteroidetes. The dietary responsiveness of the individual's microbiota varied substantially and associated inversely with its diversity, suggesting that individuals can be stratified into responders and non-responders based on the features of their intestinal microbiota.The ISME Journal advance online publication, 24 April 2014; doi:10.1038/ismej.2014.63.

PMID: 24763370

3. The role of intestinal microbiota in development of irinotecan toxicity and in toxicity reduction through dietary fibres in rats.

CPT-11 is a drug used as chemotherapy for colorectal cancer. CPT-11 causes toxic side-effects in patients. CPT-11 toxicity has been attributed to the activity of intestinal microbiota, however, intestinal microbiota may also have protective effects in CPT-11 chemotherapy. This study aimed to elucidate mechanisms through which microbiota and dietary fibres could modify host health. Rats bearing a Ward colon carcinoma were treated with a two-cycle CPT-11/5-fluorouracil therapy recapitulating clinical therapy of colorectal cancer. Animals were fed with a semi-purified diet or a semi-purified diet was supplemented with non-digestible carbohydrates (isomalto-oligosaccharides,resistant starch, fructo-oligosaccharides, or inulin) in 3 independent experiments. Changes in intestinal microbiota, bacteria translocating to mesenteric lymphnodes, cecal GUD activity, and cecal SCFA production, and the intestinal concentration of CPT-11 and its metabolites were analysed. Non-digestible carbohydrates significantly influenced feed intake, body weight and other indicators of animal health. The identification of translocating bacteria and their quantification in cecal microbiota indicated that overgrowth of the intestine by opportunistic pathogens was not a major contributor to CPT-11 toxicity. Remarkably, fecal GUD activity positively correlated to body weight and feed intake but negatively correlated to cecal SN-38 concentrations and IL1-β. The reduction in CPT-11 toxicity by non-digestible carbohydrates did not correlate to stimulation of specific bacterial taxa. However, cecal butyrate concentrations and feed intake were highly correlated. The protective role of intestinal butyrate production was substantiated by a positive correlation of the host expression of MCT1 (monocarboxylate transporter 1) with body weight as well as a positive correlation of the abundance of bacterial butyryl-CoA gene with cecal butyrate concentrations. These correlations support the interpretation that the influence of dietary fibre on CPT-11 toxicity is partially mediated by an increased cecal production of butyrate.

PMID: 24454707  Free PMC Article

4. Chicory (Cichorium intybus L.) and cereals differently affect gut development in broiler chickens and young pigs.

Dietary fiber, resistant to host-mediated digestion in the small intestine due to lack of endogenous enzymes, impacts many facets of animal health and is associated with gut development especially in young monogastrics. Furthermore, it can be used as in-feed antibiotic alternative. Chicory (Cichorium intybus L.) forage with high content of pectin (uronic acids as building blocks) is a novel class of dietary fiber that is chemically different from cereal grains (with high content of arabinoxylans). In the present study, we investigated effects of dietary inclusion of chicory forage on digestibility, gut morphology and microbiota in broilers and young pigs. In the chicken experiment, 160 1-d old broiler chicks were fed 3 nutritionally balanced diets for 30 d including a cereal-based diet and 2 diets with part of the cereals substituted with 60 and 120 g/kg chicory forage (CF60 and CF120), whereas in the pig experiment, 18 seven-wk old Yorkshire pigs were fed 3 diets for 18 d including a cereal-based diet and 2 diets with 80 and 160 g/kg chicory forage inclusion (CF80 and CF160). Our results showed that young pigs were capable to utilize chicory forage well with higher total tract apparent digestibility (TTAD) of all fiber fractions, particularly uronic acid, compared with the control (P < 0.01). In contrast, a decreased TTAD of all fiber fractions was observed in chickens fed on diet CF120 (P < 0.05). Moreover, diet induced changes in gut morphology were observed in the large intestine of chickens. The alteration of cecal mucosal thickness was further positively correlated with TTAD of non-starch polysaccharides (NSP) and its constituent sugars (P < 0.05). In addition, in pigs, terminal restriction fragment length polymorphism (T-RFLP) analysis of intestinal microbiota revealed substantial dietary effects (cereal control diet vs. chicory forage inclusion) on the relative abundance of 2 dominant bacterial phylotypes (Prevotella sp. vs. Roseburia sp.) respectively (P < 0.05). In conclusion, our data showed that chicory forage (Cichorium intybus L.), a novel dietary fiber source in animal nutrition, have potential beneficial properties as fiber ingredient in diets for both pigs and chickens.

PMID: 24341997   Free PMC Article

5. High-resolution time-of-flight mass spectrometry fingerprinting of metabolites from cecum and distal colon contents of rats fed resistant starch.

Time-of-flight mass spectrometry along with statistical analysis was utilized to study metabolic profiles among rats fed resistant starch (RS) diets. Fischer 344 rats were fed four starch diets consisting of 55 % (w/w, dbs) starch. A control starch diet consisting of corn starch was compared against three RS diets. The RS diets were high-amylose corn starch (HA7), HA7 chemically modified with octenyl succinic anhydride, and stearic-acid-complexed HA7 starch. A subgroup received antibiotic treatment to determine if perturbations in the gut microbiome were long lasting. A second subgroup was treated with azoxymethane (AOM), a carcinogen. At the end of the 8-week study, cecal and distal colon content samples were collected from the sacrificed rats. Metabolites were extracted from cecal and distal colon samples into acetonitrile. The extracts were then analyzed on an accurate-mass time-of-flight mass spectrometer to obtain their metabolic profile. The data were analyzed using partial least-squares discriminant analysis (PLS-DA). The PLS-DA analysis utilized a training set and verification set to classify samples within diet and treatment groups. PLS-DA could reliably differentiate the diet treatments for both cecal and distal colon samples. The PLS-DA analyses of the antibiotic and no antibiotic-treated subgroups were well classified for cecal samples and modestly separated for distal colon samples. PLS-DA analysis had limited success separating distal colon samples for rats given AOM from those not treated; the cecal samples from AOM had very poor classification. Mass spectrometry profiling coupled with PLS-DA can readily classify metabolite differences among rats given RS diets.

PMID: 24306331

6. Impact of whole grains on the gut microbiota: the next frontier for oats?

The gut microbiota plays important roles in proper gut function and can contribute to or help prevent disease. Whole grains, including oats, constitute important sources of nutrients for the gut microbiota and contribute to a healthy gut microbiome. In particular, whole grains provide NSP and resistant starch, unsaturated TAG and complex lipids, and phenolics. The composition of these constituents is unique in oats compared with other whole grains. Therefore, oats may contribute distinctive effects on gut health relative to other grains. Studies designed to determine these effects may uncover new human-health benefits of oat consumption. PMID: 25267244

7. Survival and synergistic growth of mixed cultures of bifidobacteria and lactobacilli combined with prebiotic oligosaccharides in a gastrointestinal tract simulator.

BACKGROUND:

Probiotics, especially in combination with non-digestible oligosaccharides, may balance the gut microflora while multistrain preparations may express an improved functionality over single strain cultures. In vitro gastrointestinal models enable to test survival and growth dynamics of mixed strain probiotics in a controlled, replicable manner.
METHODS:
The robustness and compatibility of multistrain probiotics composed of bifidobacteria and lactobacilli combined with mixed prebiotics (galacto-, fructo- and xylo-oligosaccharides or galactooligosaccharides and soluble starch) were studied using a dynamic gastrointestinal tract simulator (GITS). The exposure to acid and bile of the upper gastrointestinal tract was followed by dilution with a continuous decrease of the dilution rate (de-celerostat) to simulate the descending nutrient availability of the large intestine. The bacterial numbers and metabolic products were analyzed and the growth parameters determined.
RESULTS:
The most acid- and bile-resistant strains were Lactobacillus plantarum F44 and L. paracasei F8. Bifidobacterium breve 46 had the highest specific growth rate and, although sensitive to bile exposure, recovered during the dilution phase in most experiments. B. breve 46, L. plantarum F44, and L. paracasei F8 were selected as the most promising strains for further studies.
CONCLUSIONS:
De-celerostat cultivation can be applied to study the mixed bacterial cultures under defined conditions of decreasing nutrient availability to select a compatible set of strains.
PMID: 25045346                           Free PMC Article

8. Abnormal fibre usage in UC in remission.

OBJECTIVE:
Colonic fermentation in patients with UC in remission was compared with that in matched healthy subjects on habitual diets and when dietary fibre was increased.
DESIGN:
Fibre intake, faecal output of fibre (measured as non-starch polysaccharide (NSP)), starch, microbiota and fermentation products, and whole gut transit time (WGTT) were assessed in association with habitual diet and when dietary intake of wheat bran (WB)-associated fibre and high amylose-associated resistant starch (RS) was increased in an 8-week, randomised, single-blind, cross-over study.
RESULTS:
Despite a tendency to lower habitual fibre intake in UC patients, faecal NSP and starch concentrations were threefold higher than in controls, whereas concentrations of phenols and short-chain fatty acids, pH and WGTT were similar. Increasing RS/WB intake was well tolerated. In controls (n=10), it more than doubled faecal NSP and starch excretion (p=0.002 for both), had no effect on NSP usage and reduced WGTT (p=0.024). In UC patients (n=19), high intake of RS/WB tended to normalise gut transit, but did not increase the proportion of NSP fermented. Increasing intake of RS/WB had little effect on faecal fermentation patterns or the structure of the microbiota. However, faeces from the UC cohort had lower proportions of Akkermansia muciniphila and increased diversity within Clostridium cluster XIVa compared to controls.
CONCLUSIONS:
Gut fermentation of NSP and starch is diminished in patients with UC. This cannot be explained by abnormal gut transit and was not corrected by increasing RS/WB intake, and may be due to abnormal functioning of the gut microbiota.  PMID: 25037189

9. Diets high in resistant starch and arabinoxylan modulate digestion processes and SCFA pool size in the large intestine and faecal microbial composition in pigs.

The effects of a high level of dietary fibre (DF) either as arabinoxylan (AX) or resistant starch (RS) on digestion processes, SCFA concentration and pool size in various intestinal segments and on the microbial composition in the faeces were studied in a model experiment with pigs. A total of thirty female pigs (body weight 63·1 (sem 4·4) kg) were fed a low-DF, high-fat Western-style control diet (WSD), an AX-rich diet (AXD) or a RS-rich diet (RSD) for 3 weeks. Diet significantly affected the digestibility of DM, protein, fat, NSP and NSP components, and the arabinose:xylose ratio, as well as the disappearance of NSP and AX in the large intestine. RS was mainly digested in the caecum. AX was digested at a slower rate than RS. The digesta from AXD-fed pigs passed from the ileum to the distal colon more than twice as fast as those from WSD-fed pigs, with those from RSD-fed pigs being intermediate (P< 0·001). AXD feeding resulted in a higher number of Faecalibacterium prausnitzii, Roseburia intestinalis, Blautia coccoides-Eubacterium rectale, Bifidobacterium spp. and Lactobacillus spp. in the faeces sampled at week 3 of the experimental period (P< 0·05). In the caecum, proximal and mid colon, AXD feeding resulted in a 3- to 5-fold higher pool size of butyrate compared with WSD feeding, with the RSD being intermediate (P <0·001). In conclusion, the RSD and AXD differently affected digestion processes compared with the WSD, and the AXD most efficiently shifted the microbial composition towards butyrogenic species in the faeces and increased the large-intestinal butyrate pool size.  PMID: 25327182

 2013 Papers:

1. Resistant starch: promise for improving human health.

Ongoing research to develop digestion-resistant starch for human health promotion integrates the disciplines of starch chemistry, agronomy, analytical chemistry, food science, nutrition, pathology, and microbiology. The objectives of this research include identifying components of starch structure that confer digestion resistance, developing novel plants and starches, and modifying foods to incorporate these starches. Furthermore, recent and ongoing studies address the impact of digestion-resistant starches on the prevention and control of chronic human diseases, including diabetes, colon cancer, and obesity. This review provides a transdisciplinary overview of this field, including a description of types of resistant starches; factors in plants that affect digestion resistance; methods for starch analysis; challenges in developing food products with resistant starches; mammalian intestinal and gut bacterial metabolism; potential effects on gut microbiota; and impacts and mechanisms for the prevention and control of colon cancer, diabetes, and obesity. Although this has been an active area of research and considerable progress has been made, many questions regarding how to best use digestion-resistant starches in human diets for disease prevention must be answered before the full potential of resistant starches can be realized.

PMID: 24228189

2. Resistant starch induces catabolic but suppresses immune and cell division pathways and changes the microbiome in the proximal colon of male pigs.

Consumption of resistant starch (RS) has been associated with various intestinal health benefits, but knowledge of its effects on global gene expression in the colon is limited. The main objective of the current study was to identify genes affected by RS in the proximal colon to infer which biologic pathways were modulated. Ten 17-wk-old male pigs, fitted with a cannula in the proximal colon for repeated collection of tissue biopsy samples and luminal content, were fed a digestible starch (DS) diet or a diet high in RS (34%) for 2 consecutive periods of 14 d in a crossover design. Analysis of the colonic transcriptome profiles revealed that, upon RS feeding, oxidative metabolic pathways, such as the tricarboxylic acid cycle and β-oxidation, were induced, whereas many immune response pathways, including adaptive and innate immune system, as well as cell division were suppressed. The nuclear receptor peroxisome proliferator-activated receptor γ was identified as a potential key upstream regulator. RS significantly (P < 0.05) increased the relative abundance of several butyrate-producing microbial groups, including the butyrate producers Faecalibacterium prausnitzii and Megasphaera elsdenii, and reduced the abundance of potentially pathogenic members of the genus Leptospira and the phylum Proteobacteria. Concentrations in carotid plasma of the 3 main short-chain fatty acids acetate, propionate, and butyrate were significantly higher with RS consumption compared with DS consumption. Overall, this study provides novel insights on effects of RS in proximal colon and contributes to our understanding of a healthy diet.

PMID: 24132577

3. Diet, genes, and microbes: complexities of colon cancer prevention.

Colorectal cancer is one of the leading causes of cancer-related deaths in the United States, and generally, as countries climb the economic ladder, their rates of colon cancer increase. Colon cancer was an early disease where key genetic mutations were identified as important in disease progression, and there is considerable interest in determining whether specific mutations sensitize the colon to cancer prevention strategies. Epidemiological studies have revealed that fiber- and vegetable-rich diets and physical activity are associated with reduced rates of colon cancer, while consumption of red and processed meat, or alcoholic beverages, and overconsumption as reflected in obesity are associated with increased rates. Animal studies have probed these effects and suggested directions for further refinement of diet in colon cancer prevention. Recently a central role for the microorganisms in the gastrointestinal tract in colon cancer development is being probed, and it is hypothesized that the microbes may integrate diet and host genetics in the etiology of the disease. This review provides background on dietary, genetic, and microbial impacts on colon cancer and describes an ongoing project using rodent models to assess the ability of digestion-resistant starch in the integration of these factors with the goal of furthering colon cancer prevention.

KEYWORDS:

colon cancer; diet; genetics; microbiome; microbiota; nutrition; prevention.

PMID: 24129759

4. Gut microbes, diet, and cancer.

An expanding body of evidence supports a role for gut microbes in the etiology of cancer. Previously, the focus was on identifying individual bacterial species that directly initiate or promote gastrointestinal malignancies; however, the capacity of gut microbes to influence systemic inflammation and other downstream pathways suggests that the gut microbial community may also affect risk of cancer in tissues outside of the gastrointestinal tract. Functional contributions of the gut microbiota that may influence cancer susceptibility in the broad sense include (1) harvesting otherwise inaccessible nutrients and/or sources of energy from the diet (i.e., fermentation of dietary fibers and resistant starch); (2) metabolism of xenobiotics, both potentially beneficial or detrimental (i.e., dietary constituents, drugs, carcinogens, etc.); (3) renewal of gut epithelial cells and maintenance of mucosal integrity; and (4) affecting immune system development and activity. Understanding the complex and dynamic interplay between the gut microbiome, host immune system, and dietary exposures may help elucidate mechanisms for carcinogenesis and guide future cancer prevention and treatment strategies.

PMID: 24114492

5. Dietary red meat aggravates dextran sulfate sodium-induced colitis in mice whereasresistant starch attenuates inflammation.

BACKGROUND:

Although a genetic component has been identified as a risk factor for developing inflammatory bowel disease, there is evidence that dietary factors also play a role in the development of this disease.

AIMS:

The aim of this study was to determine the effects of feeding a red meat diet with and without resistant starch (RS) to mice with dextran sulfate sodium (DSS)-induced colitis.

METHODS:

Colonic experimental colitis was induced in Balb/c mice using DSS. The severity of colitis was evaluated based on a disease activity index (based on bodyweight loss, stool consistency, rectal bleeding, and overall condition of the animal) and a histological score. Estimations were made of numbers of a range of different bacteria in the treatment pools of cecal digesta using quantitative real-time PCR.

RESULTS:

Consumption of a diet high in red meat increased DSS-induced colitis as evidenced by higher disease activity and histopathological scores. Addition of RS to the red meat diet exerted a beneficial effect in acute DSS-induced colitis. Subjective analysis of numbers of a range of bacterial targets suggest changes in the gut microbiota abundance were induced by red meat and RS treatments and these changes could contribute to the reported outcomes.

CONCLUSIONS:

A dietary intake of red meat aggravates DSS-induced colitis whereas co-consumption of resistant starch reduces the severity of colitis.

PMID: 23990000

6. In vitro characterization of the impact of selected dietary fibers on fecal microbiotacomposition and short chain fatty acid production.

The effects of six dietary fibers [pectin, guar gum, inulin, arabinoxylan, β-glucan, and resistant starch] on the human fecal microbiota during in vitro fermentation were determined. Bifidobacterium increased almost 25% on pectin compared with the control; a significant increase in Bifidobacterium adolescentis type-2 was observed on resistant starch. Bacteroides exhibited a positive correlation with propionate/short chain fatty acid (SCFA) production (r = 0.59, p < 0.01), while Ruminococcaceae and Faecalibacterium displayed positive correlations with butyrate/SCFA production (r = 0.39, 0.54, p < 0.01). A negative correlation was detected between inulin utilization and Subdoligranulum (r = -0.73, p ≤ 0.01), while strong positive relationships were found between β-glucan utilization and Firmicutes (r = 0.73, p ≤ 0.01) and resistant starch utilization and Blautia wexlerae (r = 0.82, p < 0.01). Dietary fibers have specific and unique impacts on intestinal microbiota composition and metabolism. These findings provide a rationale for the development of functional ingredients targeted towards a targeted modulation of the gut microbiota.

PMID: 23831725

7. Resistant starch from high amylose maize (HAM-RS2) reduces body fat and increases gut bacteria in ovariectomized (OVX) rats.

OBJECTIVE:

Obesity after menopause is a health concern for older females. Changes in the microbiota are likely to occur with this condition. Modifying the microbiota with a prebiotic is a plausible strategy for improving the health of menopausal females.

DESIGN AND METHODS:

Resistant starch type 2 from high-amylose maize (HAM-RS2) was used as a prebiotic in rats in a 2 × 2 factorial study with two levels of HAM-RS2 (0 or 29.7% of weight of diet) referred to as energy control (EC) and HAM-RS2 diets, respectively; and two levels of surgery, ovariectomized (OVX) and sham.

RESULTS:

In a 6-week, postsurgery recovery period, OVX rats gained more body weight with consumption of a similar amount of food. Subsequently, consumption of HAM-RS2 versus EC diets resulted in reduced abdominal fat in both OVX and sham rats; but when normalized for disemboweled body weight (body weight minus GI tract), there was no effect of surgery, only reduction with HAM-RS2. Targeted bacterial populations were estimated that are known to ferment HAM-RS2 or metabolize the products of that initial fermentation. OVX and sham rats demonstrated increased bacterial levels with dietary HAM-RS2 for all bacteria. Additionally, culture techniques and qPCR provided similar results.

CONCLUSION:

This study shows that, as expected, OVX increases adiposity. However, contrary to previous effects seen in obese mice, this did not prevent fermentation of HAM-RS2 and consequently, the fat gain associated with OVX was attenuated.

PMID: 23784900

8. Hydrogenotrophic microbiota distinguish native Africans from African and European Americans.

Reduced susceptibility to sporadic colorectal cancer in native Africans (NA) is correlated with low consumption of animal products and greater microbial production of colonic methane. In this context, two hydrogenotrophic microbial groups are of interest, methanogenic Archaea (MA) utilizing H2 to produce methane and sulfate-reducing bacteria (SRB) generating hydrogen sulfide, which has been linked with chronic inflammatory disorders of the colon. In the present study, stool samples from NA, consuming a diet high in resistant starch and low in animal products, and from African Americans (AA) and European Americans (EA), both consuming a typical Western diet, were examined for genetic diversity and structure of Archaea, MA and SRB communities. In general, a greater proportion of NA than AA and EA harboured the full range of targeted hydrogenotrophic groups. Terminal restriction fragment length polymorphism analysis of 16S rRNA genes and specific functional genes, combined with multivariate statistical analyses, revealed that NA harboured more diverse and different Archaea and MA populations than AA and EA. Also, NA harboured significantly distinct SRB populations compared with AA and EA. Taken together, these data are consistent with diet selecting for distinct hydrogenotrophic microbiota.

PMID: 23760794

9. Effects of dietary fibers and their mixtures on short chain fatty acids and microbiota in mice guts.

Dietary fiber (DF) can be broken down into short-chain fatty acids (SCFAs) such as acetic, propionic and n-butyric acid by gut microbiota to obtain energy. Therefore, dietary fibers have effects on the balance of gut microbiota and the production of SCFAs. In the four-week feeding, mice were fed with four dietary fibers, including pectin, resistant starch (RS), fructo-oligosaccharide (FOS) and cellulose. The results showed that the mice body-weight gain was the smallest (7.0 ± 2.3 g) when the mixture of RS-FOS-cellulose was ingested, followed by the mixture of RS-cellulose (7.2 ± 3.5 g) and FOS-cellulose (8.3 ± 2.5 g). Ingestion of the mixture of pectin-FOS-cellulose, RS-FOS and RS-FOS-cellulose can respectively increase the diversity of the gut microbiota with 12, 11 and 11 terminal restriction fragments (TRFs) detected (digested by Hha I). The maximum amount of total SCFAs were produced by the mixture of FOS-cellulose (5.504 ± 0.029 μmol mL(-1)), followed by pectin-FOS-cellulose (3.893 ± 0.024 μmol mL(-1)) and pectin-RS-FOS-cellulose (3.309 ± 0.047 μmol mL(-1)). In conclusion, the addition of DFs (pectin, RS, FOS and cellulose), in single or mixture pattern, can exert different effects. An amount of 10.7% of single DF in the diet cannot be conducive to the balance of gut microbiota after ingestion for a long time, however, it can help with body weight loss like the mixtures of DFs in this study; FOS is a very important component in the mixture of DFs for both the balance of the gut microbiota and the production of SCFAs.

PMID: 23669739

10. Some are more equal than others: the role of "keystone" species in the degradation of recalcitrant substrates.

The microbial communities found in the mammalian large intestine and rumen efficiently degrade many recalcitrant substrates that are resistant to the host's digestive enzymes. These communities are known from molecular profiling to be highly diverse at the species and strain level, but it may be that only certain specialized organisms ("keystone species") have the ability to initiate degradation of such substrates, thus releasing energy on which the rest of the community depends. We have recently reported that Ruminococcus bromii has a superior ability to degrade certain forms of particulate resistant starch (RS) when compared with other highly abundant species of amylolytic bacteria found in the human colon and have presented evidence that this bacterium provides an example of a keystone species within the microbial community with respect to RS fermentation. The concept of keystone species can be equally relevant to other activities, e.g., those involved in stabilizing the community.

KEYWORDS:

anaerobic bacteria; cross-feeding; human colon; keystone species; microbial consortia; microbiota;resistant starch

PMID: 23549436  Free PMC Article

11. Microbiota and healthy ageing: observational and nutritional intervention studies.

Hundred years ago Metchnikoff associated human health and particularly healthy ageing with a specific type of gut microbiota. Classical culture methods associated a decrease in bifidobacteria and an increase in enterobacteria with ageing. Modern molecular methods blurred this simple picture and documented a substantial inter-individual variability for the gut microbiome even when stratifying the elderly subjects according to health status. Nutritional interventions with resistant starch showed consistent gut microbiota changes across studies from different geographical areas and prebiotic supplementation induced a 10-fold increase in gut bifidobacteria. However, in the ELDERMET study, microbiota changes do not precede, but follow the changes in health status of elderly subjects possibly as a consequence of diet changes.

PMID: 23527905  Free PMC Article

12. Resistant starch: a promising dietary agent for the prevention/treatment of inflammatory bowel disease and bowel cancer.

PURPOSE OF REVIEW:

Resistant starch represents a diverse range of indigestible starch-based dietary carbohydrates. Resistant starch has been investigated in the past for its effects on bowel health (pH, epithelial thickness, and apoptosis of colorectal cancer cells); reduction in postprandial glycemia; increased insulin sensitivity; and effects on the gut microbiome. This review highlights advances as resistant starch gains clinical relevance as a potential treatment/preventive tool for diseases such as colorectal cancer (CRC) and diabetes.

RECENT FINDINGS:

Recent articles have evaluated the comparative physiological effects of different types of resistant starch and investigated the effects of resistant starch on blood lipids, body weight, and defining resistant starch-induced changes to the microbiome that may be important in health and disease. The most novel and relevant recent data describe a role for resistant starch in ameliorating inflammation; the use of resistant starch for optimal bowel health and prevention of CRC; and, further, that the systemic effects of resistant starch may be important for the treatment of other forms of cancer, such as breast cancer.

SUMMARY:

This review describes advances in resistant starch research highlighting the gastrointestinal effects that are now being linked to systemic, whole body effects with clinical relevance. These effects have important implications for overall health and the prevention or amelioration of various chronic diseases.

PMID: 23385525

13. A diet high in resistant starch modulates microbiota composition, SCFA concentrations, and gene expression in pig intestine.

Resistant starch (RS) is highly fermentable by microbiota in the colon, resulting in the production of SCFAs. RS is thought to mediate a large proportion of its health benefits, including increased satiety, through the actions of SCFAs. The aim of this study was to investigate the effects of a diet high in RS on luminal microbiota composition, luminal SCFA concentrations, and the expression of host genes involved in SCFA uptake, SCFA signaling, and satiety regulation in mucosal tissue obtained from small intestine, cecum, and colon. Twenty adult female pigs were either assigned to a digestible starch (DS) diet or a diet high in RS (34%) for a period of 2 wk. After the intervention, luminal content and mucosal scrapings were obtained for detailed molecular analysis. RS was completely degraded in the cecum. In both the cecum and colon, differences in microbiota composition were observed between DS- and RS-fed pigs. In the colon these included the stimulation of the healthy gut-associated butyrate-producing Faecalibacterium prausnitzii, whereas potentially pathogenic members of the Gammaproteobacteria, including Escherichia coli and Pseudomonas spp., were reduced in relative abundance. Cecal and colonic SCFA concentrations were significantly greater in RS-fed pigs, and cecal gene expression of monocarboxylate transporter 1 (SLC16A1) and glucagon (GCG) was induced by RS. In conclusion, our data show that RS modulates microbiota composition, SCFA concentrations, and host gene expression in pig intestine. Combined, our data provide an enhanced understanding of the interaction between diet, microbiota, and host.

PMID: 23325922 Free full text

14. Prebiotics to fight diseases: reality or fiction?

Bacteria living in the gastrointestinal tract are crucial for human health and disease occurrence. Increasing the beneficial intestinal microflora by consumption of prebiotics, which are 'functional foods', could be an elegant way to limit the number and incidence of disorders and to recover from dysbiosis or antibiotic treatments. This review focuses on the short-chain low-digestible carbohydrates (LDCs) which are metabolized by gut microbiota serving as energy source, immune system enhancers or facilitators of mineral uptake. Intake of foods containing LDCs can improve the state of health and may prevent diseases as for example certain forms of cancer. Given the large number of different molecules belonging to LDCs, we focused our attention on fructans (inulin, fructo-oligosaccharides), galacto-oligosaccharides and resistant starches and their therapeutic and protective applications. Evidence is accumulating that LDCs can inhibit bacterial and viral infections by modulating host defense responses and by changing the interactions between pathogenic and beneficial bacteria. Animal studies and studies on small groups of human subjects suggest that LDCs might help to counteract colorectal cancer, diabetes and metabolic syndrome. The action mechanisms of LDCs in the human body might be broader than originally thought, perhaps also including reactive oxygen species scavenging and signaling events.

PMID: 23280537

15. Effects of potato fiber and potato-resistant starch on biomarkers of colonic health in rats fed diets containing red meat.

The effects of red meat consumption with and without fermentable carbohydrates on indices of large bowel health in rats were examined. Sprague-Dawley rats were fed cellulose, potato fiber, or potato-resistant starch diets containing 12% casein for 2 wk, then similar diets containing 25% cooked beef for 6 wk. After week 8, cecal and colonic microbiota composition, fermentation end-products, colon structure, and colonocyte DNA damage were analyzed. Rats fed potato fiber had lower Bacteroides-Prevotella-Porphyromonas group compared to other diet groups. Colonic Bifidobacterium spp. and/or Lactobacillus spp. were higher in potato fiber and potato-resistantstarch diets than in the cellulose diet. Beneficial changes were observed in short-chain fatty acid concentrations (acetic, butyric, and propionic acids) in rats fed potato fiber compared with rats fed cellulose. Phenol and p-cresol concentrations were lower in the cecum and colon of rats fed potato fiber. An increase in goblet cells per crypt and longer crypts were found in the colon of rats fed potato fiber and potato-resistant starch diets. Fermentable carbohydrates had no effect on colonic DNA damage. Dietary combinations of red meat with potato fiber or potato-resistant starch have distinctive effects in the large bowel. Future studies are essential to examine the efficacy of different types of nondigestible carbohydrates in maintaining colonic health during long-term consumption of high-protein diets.

PRACTICAL APPLICATION:

Improved understanding of interactions between the food consumed and gutmicrobiota provides knowledge needed to make healthier food choices for large bowel health. The impact of red meat on large bowel health may be ameliorated by consuming with fermentable dietary fiber, a colonic energy source that produces less harmful by-products than the microbial breakdown of colonic protein for energy. Developing functional red meat products with fermentable dietary fiber could be one way to promote a healthy and balanced macronutrient diet.

PMID: 22950602