gut microbiome

  • Probiotics for Digestive Health

    Probiotics for Digestive Health Dallas Clouatre

    As pointed out in past TotalHealth articles, many fungi and bacteria found in foods are beneficial to health. Whether one is discussing breads, cheeses, fermented tofu, wines, yoghurt, sauerkraut, kimchi or a number of other items, very often it turns out that traditional cooking and preserving techniques involving fungi and bacteria offer many benefits that are lost with modern alternatives.

    This having been said, a major benefit of modern food science is the ability to supply beneficial bacteria in concentrated forms. The following discussion is intended to answer questions regarding the class of dietary supplements referred to as probiotics. Readers who wonder why some products have single strains and others offer many, why there often are numbers or other designations after Latin names of the bacteria, what benefits might be expected and how soon, etc., should read on. The species and strains mentioned happen to be ones with which the author is most familiar.

    Do different probiotic strains affect the body in different ways? Do people benefit from having more of one strain than another?

    The human gut consists of a series of microenvironments. Except for the stomach and the upper two thirds of the small intestine, there are differing bacteria and ratios of bacteria in each of these areas, starting with the mouth. In fact, the human gastrointestinal tract contains a large and diverse population of microorganisms—over 800 different bacterial species comprising nearly 100 trillion living organisms. The composition of this gut flora varies among individuals depending on diet, age, medication (antibiotics), stress, and physiological conditions. Not surprisingly, different probiotics perform different functions and offer different benefits. One big divide, of course, is between the two most important groups of typical probiotic bacterial species, Lactobacilli, found mostly in the lower small intestine and upper large intestine, and Bifidobacteria, found mostly in the large intestine, i.e., the areas of lower pH (meaning more acidic).

    Broadly speaking, the Lactobacilli act on sugars and starches to create lactic acid, among other things. For instance, L. acidophilus La-14 (La-14 indicates the strain within the particular species) assists in breaking down lactose (milk sugar) and 15 other carbohydrates and this may improve digestion of dairy products by those individuals who are lactose intolerant. Clinical trials have shown that this strain may improve immune response and bowel regularity. It works especially well in conjunction with another bacteria strain, L. rhamnosus R0011. Interestingly, L. rhamnosus R0011 in conjunction with L. helveticus R0052 in humans enhances the eradication of H. pylori (a cause of stomach ulcers) when ingested in combination with conventional medical treatment.

    Bifidobacteria, especially such as B. longum BB536 (Morinaga strain), have been shown to colonize the intestine, stimulate immune response, and promote the growth of other beneficial bacteria. BB536 also decreased the incidence of influenza in seniors in trials. Blood analysis showed significantly higher bactericidal activity of neutrophils and higher NK cell activity at the fifth week of administration compared to pre-administration. There has also been evidence reported that suggests BB536 can help modulate allergies and possess antiallergenic effects. Even more recent research is looking at the benefits of this strain in the areas of brain inflammation and dementia.

    The finding that certain strains of probiotics reduce excessive inflammation by means of modulation of immune and other responses via the gut is one of the major advances in the knowledge of probiotics in recent years.

    Inasmuch as different probiotic species and different strains of the same species often provide different and distinct benefits and also often interact to lead to yet other results, there are good reasons for supplementing with more than one strain and/or species (I refer loosely and not entirely scientifically to "species" here to distinguish also, for instance, Saccharomyces boulardii, which is not another bacterial strain, but instead a probiotic yeast). Similarly, different supplemental probiotics may be more to be desired at certain ages or under particular conditions. No single strain can easily fulfill all these requirements. A mixture of species, therefore, is usually most suitable for supplementation. The most desirable properties of a good probiotic are:

    • Compatibility among the strains
    • Ability to survive passage through the digestive tract
    • Stability under normal gastric conditions
    • Resistance to bile salts
    • Adherence to intestinal mucosa
    • Colonization of the human intestinal tract and/or extended residence time
    • Safety with regard to human use
    • Production of natural antimicrobial substances
    • Antagonism against unfriendly and putrefactive bacteria
    • Stability during storage under normal conditions

    When purchasing a probiotic supplement, how many different strains should be in supplement and are all the strains in equal parts?

    There is no one answer to this question. The probiotic yeast, Saccharomyces boulardii, typically is supplemented by itself before, during and immediately after antibiotic treatment, but otherwise may be supplemented in general with a mixture with bacterial probiotics. As a rule, it is best to supplement at least the two primary species of probiotics, Lactobacilli, found mostly in the lower small intestine and upper large intestine, and Bifidobacteria, found mostly in the large intestine. Three to eight species and/or strains is a common number. Keep in mind that these species and strains must be compatible both in the delivery format and after administered.

    What fibers are effective prebiotics?

    Let's start by defining the role of prebiotics. According to researchers in the field, "Prebiotics are supplements or foods that contain a nondigestible food ingredient that selectively stimulates the favorable growth and/or activity of indigenous probiotic bacteria. Human milk contains substantial quantities of prebiotics." 1 Some researched prebiotic fibers include trans-galactooligosaccharide, oligofructose, inulin, larch arabinogalactin, resistant starch, pectin, beta-glucans, xylooligosaccharides, and oligofructose-enriched inulin. Recently, scientists have begun to recognize that a number of polyphenols have prebiotic properties, although there as yet is no consensus as to the amounts required for benefits. For instance, proanthocyanidins and other compounds found in grape seed and red wine can positively affect gut microbial health, as can related compounds found in dark/minimally processed chocolate and in cranberries. This is an emerging area of knowledge.

    What is the importance of pH in digestive health and how can dietary supplements support a balanced pH?

    The degree of acidity or alkalinity of a given region of the gut can be given as its pH. The stomach should have a very low pH (relatively acidic) prior to meals, e.g., a pH of 2 or below, because this is needed to digest proteins and to provide a protective barrier against bacterial invasion of the rest of the gastrointestinal tract. A low pH in the stomach also is required to maintain the tonus of the esophageal sphincter to avoid "heartburn" and other gastrointestinal reflux conditions. The upper small intestine may approach a neutral pH of 6 and slightly above after pancreatic digestive fluids are mixed into foods coming from the stomach; this higher pH is required for the digestion of fats and for the actions of pancreatic enzymes. As foods proceed through the small intestine, the pH should slowly decrease as a result of bacterial action producing lactic and other acids. Short-chain fatty acids produced in the intestines exert a number of health effects. The return to a lower pH in the large intestine is required to produce peristalsis to maintain the proper passage of food through the bowel.

    Hydrochloric acid precursor supplements can be taken to improve the production of gastric acid in the stomach. Betain HCl commonly is used for this purpose.

    How do enzymes, herbs and botanicals affect acute symptoms like heartburn, indigestion, nausea or diarrhea?

    Herbs can help for a variety of reasons. Chamomile is famous for calming properties and typically is taken as an antispasmodic and anti-inflammatory. Peppermint, especially the oil delivered by enteric soft gelatin capsules, is another item for calming the GI-tract. Type "peppermint irritable bowel" into PubMed and there will be 60 or more hits. Again, it is an antispasmodic. Ginger is widely touted—and human trials confirm this—as being good for several forms of nausea. Readers of past TotalHealth articles may recall that the Asian herb/food known as bitter melon, especially in its wild forms, improves various aspects of gastrointestinal health. (Bitter melon is best consumed with small amounts of "warming" herbs such as ginger or turmeric.)

    A review published in 2012 concluded, "Amongst the most important we can find [with digestion-enhancing properties] [are] ginger, peppermint, aniseed and fennel, citrus fruits, dandelion and artichoke, melissa and chamomile, but many more have a significant body of experimental data available."2

    Pancreatin, which includes trypsin, amylase and lipase, is specifically produced by the body to digest proteins, carbohydrates and fats under the relatively neutral pH conditions found in the stomach at the end of acid digestion and, primarily, in the small intestine. What most people do not realize is that the body tends to conserve digestive enzymes. Long-term use of digestive enzymes can help increase the body's own reserves of these enzymes for better digestion.

    Although enzymes can help acutely with indigestion, this may not be the best way of conceptualizing their benefits. Retailers should try to find ways to highlight the contrast between treating the symptoms of poor digestion and actually improving digestion. For instance, as a practical matter, no one has too much acid in the stomach, so quite obviously taking proton pump inhibitors makes worse an underlying condition—too little gastric acid. Blocking acid release may make gastroesophageal reflux disease (GERD) temporarily less painful, but it does not address why GERD exists.

    How does "cleansing" support digestive health? What is a safe and effective cleanse?

    It is important to distinguish between detoxification and cleansing approaches. Detoxification programs typically focus on the liver and involve the endogenous Phase I and Phase II detoxification systems. Cleansing programs, in contrast, focus on the large intestine and are based on theories of autointoxication from partially digested foods, especially meat and other animal foods, leading to the build-up of mucus and other wastes in the intestines with the absorption of these toxins into the blood.

    There is a grain of truth to cleansing theories. A considerable part of the toxins and waste products of the body, such as spent hormones, are eliminated through the bile and thus via the stool. Likewise, it certainly is true that a lack of fiber in the diet and dysbiosis in the gut can lead to toxins being reabsorbed multiple times before being fully excreted from the body. These two pieces fit together because in its detoxification processes, the body binds toxins in a variety of ways, two of which are glucuronidation and sulfation, and then disposes of the toxins via the bile. Without adequate fiber, including fiber that can support the growth of friendly bacteria in the gut, toxins disposed via the bile can be reabsorbed many times before eventually being eliminated from the body. Similarly, without the proper fiber, toxins can influence the health of the cells lining the large intestine. Especially important in this light are synbiotics, meaning combinations of prebiotics (such as fiber) and probiotics that work well together to deliver greater health benefits.

    Nevertheless, many of the claims of cleansing programs seem suspect. For instance, the large intestine turns over the cells that make up the intestinal lumen roughly every three days, so claims of a build-up of impacted fecal matter (as opposed to constipation, something entirely different) do not match the evidence.

    What can a cleansing program accomplish? First, it can mark a transition to a new general diet. Consuming more fiber (soluble, semisoluble and insoluble) is well established to improve constipation, diverticulosis, some forms of irritable bowel, and to protect against colorectal cancer. How much is needed? Most estimates are 20–35 grams per day rather than the usual American consumption of only 10–15 grams per day. Some health writers suggest consuming herbal gums such as frankincense, myrrh and mastic gum during this period.

    Second, dysbiosis is a real issue and a turnover in the make-up of the stool through the addition of fiber and probiotics—a synbiotic approach—can help to change the intestinal milieu. Again, constipation, diverticular disease and forms of inflammatory and irritable bowel can be improved by this combination approach.

    The best reason to undertake a cleanse is to transition to a diet higher in vegetables, whole grains, legumes and fiber-rich foods in general. This also should help the system move to a different make-up of intestinal bacteria. A very simple way to accomplish this is to add approximately 10 grams of good quality fiber to each meal and, assuming that one does not have a blocked bile duct, to take supplements that increase the release of bile. These include gentian, artichoke leaf, chicory root, dandelion root and yellow dock. At the same time, a good probiotic should be started to positively influence the composition of the bacteria found in the gut. The first few days of such a cleanse may be a bit uncomfortable and be characterized by unusual gas and bloating, but by the end of one or two weeks things should stabilize. Higher fiber intake from whole fruit (not juice), vegetables, legumes and whole grains should continue.

    Probiotics for Digestive Health

    HOW MANY BACTERIA IS ENOUGH AND HOW MANY IS TOO MUCH?
    Too often the impression is that if one or two billion colony forming units (CFU) of a probiotic species is good, then 50 or 100 billion must be better. Research and real life experience do not always agree with this! There is a strong argument to be made that approximately two billion CFU of any given strain is quite enough for everyday usage if the species and its strain is, in fact, appropriate for the intended purpose. Formulas containing multiple species and multiple strains might supply CFU in the range of 10–15 billion using this reasoning.

    Lactobacillus acidophilus is generally considered safe for most people. Gas, upset stomach, and diarrhea are potential side effects in some people (not on antibiotic therapy) who take more than 1 to 2 billion L. acidophilus CFUs daily.3

    Supplement shoppers examining probiotic products need to keep in mind that there are many more types of desirable organisms in the gastrointestinal tract than merely Bifidobacilli and Lactobacilli. For instance, according to Tim Spector, professor of genetic epidemiology at Kings College London and director of the British Gut Microbiome project, a "healthy gut is like a perfect English garden. You've got a diversity of microbes of all types, all living together and feeding off each other's by products—nothing is wasted."4

    Overloading the GI-tract with huge numbers of probiotic bacteria can crowd out the diversity of bacteria that should be found in the gut. The result can be so-called "cleansing" episodes of either or both diarrhea and constipation. Moreover, excess supplementation or supplementation with probiotic strains that do not match a person's constitution, rather than addressing the issues of gas and bloating, actually can increase these. If a probiotic supplement program still continues to cause gas and bloating after two weeks, a different source of probiotics may be found to be more appropriate.

    Finally, do not overlook the fact that actual food sources of probiotics often are the best sources. This means real cheeses with live cultures, live yoghurt, real rather than artificially soured sauerkraut, traditionally prepared kimchi and other Asian soured vegetables, traditionally prepared and preserved pickles (all of these will be in the refrigeration section of the store), live sour creams and sour milks, naturally yeast-leavened breads made the traditional way, and so forth and so on. Among other benefits, these foods not only often are more nutritious, but also simply generally taste better.


    References:
    1. Pediatrics. 2010 Dec;126(6):1217–31.)
    2. Int J Food Sci Nutr. 2012 Mar;63 Suppl 1:82–9.)
    3. http://umm.edu/health/medical/altmedsupplement/lactobacillus-acidophilus
    4. http://www.foodmanufacture.co.uk/Ingredients/Gut-health-governs-obesity-immune-response-and-moods
  • What If Gluten Isn’t the Culprit?

    What If Gluten Isn’t the Culprit? Dallas Clouatre

    In many older detective stories, the punch line famously is, "the butler did it." In the minds of many contemporary Americans, gluten is the "butler." Increasingly, when individuals experience symptoms such as fatigue, headaches and gastrointestinal distress, including gas, bloating and diarrhea, gluten is called out as the culprit. The passage of partially digested or undigested gluten through the intestines and the gut barrier may also contribute to additional symptoms not limited to those involving the development of food sensitivities and intolerances. The answer in this paradigm is to avoid all gluten-containing foods, such as wheat, oats, rye, barley and spelt. The problem with this paradigm is that other than for a quite small percentage of the populace, there is little evidence that gluten per se is the culprit or that gluten avoidance will solve all or even most gluten-associated issues. This topic often leads to heated debates. Readers should be aware that the gluten-as-villain story has quite serious skeptics.1,2

    Who Reacts to Gluten?
    Gluten, a protein, is a large, complex molecule that contains thousands of folded amino acid sequences composed of globulans, albumins, glutenin and gliadin, with the gliadin fraction believed to cause most of the symptoms associated with gluten sensitivity. Gluten's exceptionally rich proline content contributes to resistance to digestion. When this big ball of peptides is insufficiently broken down, amino acid bonds within each molecule remain resulting in a partially-degraded protein that can lead to an array of symptoms. Some authorities suggest that if gluten is a sufficiently rich component of the diet (a rare situation), it will lead to reactions even in those otherwise tolerant as a result of these difficulties in digestion.

    There is a spectrum of gluten-related disorders, including celiac disease, gluten sensitivity, and wheat allergy, the latter affecting only on the order of 0.1 percent of individuals in Westernized countries.3,4 Non-celiac gluten intolerance involves heightened immunologic reaction to gluten in genetically susceptible people whereas celiac disease involves a complex autoimmune response in the small intestine to gluten ingestion.5,6 The estimated prevalence of celiac disease is approximately one percent of the populace.7

    This is where things start to become very interesting in ways that suggest that the "gluten did it" scenario may be a bit misleading. As summarized in a fine article a few years back in the New York Times, "roughly 30 percent of people with European ancestry carry predisposing genes, for example. Yet more than 95 percent of the carriers tolerate gluten just fine. So while these genes (plus gluten) are necessary to produce the disease, they're evidently insufficient to cause it."8

    This observation becomes more intriguing in light of recent blood serum studies. In one, an examination of 9,133 frozen blood samples taken from US Air Force recruits between 1948 and 1954 for the antibody that people with celiac disease produce in reaction to gluten found that only about one in seven hundred tested positive, or 0.2 percent. This was compared to rates of celiac disease among 12,768 people who either had similar years of birth (i.e. were born around 1930) or who were of a similar age to the original donors at the time of sampling (i.e. young adults today). The rates of celiac disease were 0.8 percent and 0.9 percent respectively, or a 4 to 4.5-fold increase. In other words, in populations that genetically were virtually identical, celiac rates had increased more than 400 percent in a mere 50 years.9 Another study that analyzed blood serum from more than 3,500 Americans who had been followed since 1974 found that by 1989 the prevalence of celiac disease in this cohort had doubled.10

    More recent studies have confirmed the rising risk of developing celiac among otherwise similar groups in the past. So have cross-national comparative studies. The populations in adjacent Russian Karelia and Finland are equally exposed to grain products and share partly the same ancestry, but live in completely different socioeconomic environments. The two study populations are culturally, linguistically and genetically related with predisposing gene variants are similarly prevalent in both groups. Examination of 5,500 subjects yielded a prevalence of roughly one in 100 among Finnish children whereas the same diagnostic methods indicated only one in 500 among their Russian counterparts.11

    More Intrigue
    In line with a number of studies looking at the prevalence of asthma and other forms of autoimmune disease, the Finnish/ Russian data suggest modern sanitary and dietary practices are leading to poorer health in unexpected ways. For instance, three of four Russian Karelian children harbored Helicobacter pylori in comparison with one in 20 Finnish children. H. pylori can cause ulcers and stomach cancer, but mounting evidence suggests that exposure also reduces the incidence of asthma. The author of the New York Times article mentioned above notes that one author of the Finnish study suspects that Russian Karelians' microbial wealth (exposure to a much larger variety of microbes compared to more Westernized and metropolitan populations) protects them from autoimmune and allergic diseases by strengthening the arm of the immune system that guards against such illnesses. Similarly, Yolanda Sanz, a researcher at the Institute of Agrochemistry and Food Technology in Valencia, Spain, makes a compelling case for the importance of intestinal microbes. "Years ago, Dr. Sanz noted that a group of bacteria native to the intestine known as bifidobacteria were relatively depleted in children with celiac disease compared with healthy controls. Other microbes, including native E. coli strains, were overly abundant and oddly virulent."

    Quite a number of authors have noted a possible role for longer breast-feeding of infants in helping to confirm bifidobacteria in a more dominant role in the large intestine in children and later life as well as controlling E. coli growth. Other changes in Western practices similarly may influence the role of foodstuffs. For example, a study published in 2011 found that a specially fermented wheat flour-derived product did not lead to any sort of toxic reaction after being given to celiac patients for 60 days. This is in line with research indicating that the manufacture of wheat and rye breads or pasta with durum flours by using selected sourdough lactobacilli markedly decreases the toxicity of gluten. In Western countries, cereal baked goods typically are manufactured by fast processes. As noted by researchers, this avoids the traditional long fermentation by sourdough—a cocktail of acidifying and proteolytic lactic acid bacteria—and has replaced fermentation with chemical and baker's yeast leavening agents. Under these conditions, cereal components are not degraded during manufacture.12

    Again, a number of researchers have uncovered evidence that keeping bifidobacteria and lactobacilli at sufficiently high levels in the appropriate areas of the intestines strongly influences tendencies toward autoimmune diseases.

    Other Contributors to the Modern Gluten Intolerance

    Gluten has been in the human food chain for thousands of years, yet gluten intolerance has become widespread in recent decades. Along with some items already mentioned, here is an extended list of possible culprits:

    • Changes in baking techniques; to speed processing and reduce costs, modern breads almost never are fully yeast-raised as in the past, a process that makes gluten more digestible; similarly, the long steaming of wheat and rye breads typical of Central and Eastern Europe makes breads more digestible
    • Changes in the gluten content of wheat—since the 1950s the USDA, without public notice, has been involved in wheat breeding to increase gluten content
    • Novel processing techniques when using gluten-derived compounds in foodstuffs, such as deamidation involving removing an amino group (NH2); this makes the peptides more soluble and smaller, but also increases their chances of breaching the gut lumen and activating immune responses
    • Changes in refrigeration and storage, which, in turn, change our gut bacteria and lead to novel intolerance reactions to foods
    • Reduced breast-feeding and altered feeding and weaning practices; changes in infant formulas; suspected changes in mother's milk itself at the populace at large becomes more prone to overweight and obesity plus the foods consumed by mothers change
    • C-sections becoming more common, which tends to alter the bacteria babies inherit (or do not inherit) from the mother via the birth canal
    • Reduced exposure to various dusts and other challenges from the natural world that help train the developing immune system and reduce autoimmune overreactions
    • GMOs and the chemicals linked to these are ubiquitous in the food supply

    Although, as indicated above, heightened sensitivity to gluten extends back several decades, GMOs may be true game-changers for future generations. According to Jeffrey Smith and the Institute for Responsible Technology (IRT), a "possible environmental trigger [for gluten intolerance] may be the introduction of genetically modified organisms (GMOs) to the American food supply, which occurred in the mid-1990s," describing the nine GM crops currently on the market. In soy, corn, cotton (oil), canola (oil), sugar from sugar beets, zucchini, yellow squash, Hawaiian papaya, and alfalfa, "Bt-toxin, glyphosate, and other components of GMOs, are linked to five conditions that may either initiate or exacerbate gluten-related disorders." It's the Bt-toxin in genetically modified foods that kills insects by "puncturing holes in their cells." The toxin is present in ‘every kernel' of Bt-corn and survives human digestion, with a 2012 study confirming that it punctures holes in human cells as well.

    According to an IRT report, GMO-related damage is linked to five different areas: intestinal permeability, imbalanced gut bacteria, immune activation and allergic response, impaired digestion, and damage to the intestinal wall. The IRT release also indicated that glyphosate, a weed killer sold under the brand name 'Roundup,' was found to have a negative effect on intestinal bacteria. GMO crops contain high levels of this toxin at harvest. "Even with minimal exposure, glyphosate can significantly reduce the population of beneficial gut bacteria and promote the overgrowth of harmful strains."13,14

    Sometimes the Villains Aren't Bad Guys and How To Promote the Good Guys
    A word of caution is in order regarding gut bacteria. Just as gluten may not be the primary actor in its own drama, so, too, are some "bad" bacteria not so bad after all. Above, the case of H. pylori was presented as perhaps not quite as black-and-white as normally argued. Another example is E. coli. Which E. coli? Recent research has uncovered that small molecules produced by the microbiota and related to indole extend healthspan in geriatric worms, flies, and mice.15 According to the authors of this research, the term "healthspan" describes the length of time a human or animal, while aging, can stay active and resist stress. In this research, the focus is on whether the animals live healthier, but not necessarily longer. The study identified indole and related molecules as compounds released by E. coli bacteria. Indoles may be keeping the intestinal barrier intact and/or limiting systemic inflammatory effects. Moreover, there are specialty E. coli strains that are well-researched as excellent probiotics useful in treating a number of gastro-intestinal disorders and even helping to maintain remission in patients with ulcerative colitis.16,17 The trick is to encourage the presence of the right E. coli to limit the growth of the wrong E. coli.

    What about daily foods that boost good gut microbiome, including diversity in the gut? It is important to be able to promote gut health via daily food habits rather than relying on prebiotic supplements alone. Here are some everyday choices according to a 2016 survey conducted in Europe:18

    Good foods for boosting the gut microbiome

    • Fruit and vegetables
    • Yogurt
    • Coffee
    • Tea
    • Red wine
    Bad habits that hurt the microbial ecosystem
    • A high-calorie diet
    • A high-carbohydrate diet
    • Sugar-sweetened beverages
    • Frequent snacks

    Medications have the biggest influence on gut microbiome diversity. Antibiotics, proton-pump inhibitors and metformin (a common diabetes drug) all are linked to lower microbiome diversity.

    Conclusion
    Blaming gluten for GI-tract issues, allergies and even weight gain is akin to the pharmaceutical world's "magic bullet" approach once encapsulated as "one disease, one drug." In reality, in the modern Western world a host of changes have taken place in food growing and processing along with changes in personal habits and some of these changes have led to an otherwise and previously relatively innocuous protein, gluten, becoming a source of health issues. Eliminating gluten from the diet (along with wheat, oats, rye, barley and spelt) is not the answer to environmental mistakes, such as the growing prevalence of poor bread-making practices and the use of GMOs. A better approach is to learn the nature of the non-health- promoting practices and then to find alternatives.

    References:

    1. Gaesser GA, Angadi SS. Gluten-free diet: imprudent dietary advice for the general population. J Acad Nutr Diet. 2012 Sep;112(9):1330–3.
    2. Shewry PR, Hey SJ. Do we need to worry about eating wheat? Nutr Bull. 2016 Mar;41(1):6–13.
    3. Piezak M. Celiac disease, wheat allergy, and gluten sensitivity: When gluten free is not a fad. JPEN J Parental Enterol Nutr. 2012;36(suppl 1):68S–75S.
    4. Sapone A, Bai JC, Ciacci C, et al. Spectrum of gluten-related disorders: Consensus on new nomenclature and classification. BMC Med. 2012; 10:13.
    5. Hadjivassiliou M, Grunewald RA, Davies-Jones GAB. Gluten sensitivity as a neurological illness. J Neurol Neurosurg Psychiatry. 2002;72(5): 560–3.
    6. Briani C, Samaroo D, Alardini A. Celiac disease: From gluten to autoimmunity. Autoimmunity Rev. 2008;7(8):644–50.
    7. Catassi C, Fassano A. Celiac disease. Curr Opin Gastroenterol. 2008;24(6):687–91.
    8. Moises Velasquez-Manoff. Who Has the Guts for Gluten? New York Times. February 23, 2013.
    9. Rubio-Tapia A, Kyle RA, Kaplan EL, Johnson DR, Page W, Erdtmann F, Brantner TL, Kim WR, Phelps TK,
    10. Lahr BD, Zinsmeister AR, Melton LJ 3rd, Murray JA. Increased prevalence and mortality in undiagnosed celiac disease. Gastroenterology. 2009 Jul;137(1):88–93.
    11. Catassi C, Kryszak D, Bhatti B, Sturgeon C, Helzlsouer K, Clipp SL, Gelfond D, Puppa E, Sferruzza A, Fasano A. Natural history of celiac disease autoimmunity in a USA cohort followed since 1974. Ann Med. 2010 Oct;42(7):530–8.
    12. Kondrashova A, Mustalahti K, Kaukinen K, Viskari H, Volodicheva V, Haapala AM, Ilonen J, Knip M, Mäki M, Hyöty H; Epivir Study Group. Lower economic status and inferior hygienic environment may protect against celiac disease. Ann Med. 2008;40(3):223–31.
    13. Francavilla R, De Angelis M, Rizzello CG, Cavallo N, Dal Bello F, Gobbetti M. Selected Probiotic Lactobacilli Have the Capacity To Hydrolyze Gluten Peptides during Simulated Gastrointestinal Digestion. Appl Environ Microbiol. 2017 Jun 30;83(14).
    14. GMOs linked to gluten disorders plaguing 18 million Americans https://www.rt.com/usa/gmo-gluten-sensitivitytrigger-343/
    15. Are Genetically Modified Foods a Gut-Wrenching Combination? http://responsibletechnology.org/glutenintroduction/
    16. "Chemicals from gut bacteria maintain vitality in aging animals: Indoles help worms/flies/mice live stronger for longer." ScienceDaily. ScienceDaily, 21 August 2017. www.sciencedaily.com/releases/2017/08/170821151052.htm.
    17. Fuchssteiner H, Nigl K, Mayer A, Kristensen B, Platzer R, Brunner B, Weiß I, Haas T, Benedikt M, Gröchenig HP, Eisenberger A, Hillebrand P, Reinisch W, Vogelsang H. [Nutrition and IBD-Consensus of the Austrian Working Group of IBD (Inflammatory Bowel Diseases) of the ÖGGH]. Z Gastroenterol. 2014 Apr;52(4):376–86. 17. Enck P, Zimmermann K, Menke G, Klosterhalfen S. Randomized controlled treatment trial of irritable bowel syndrome with a probiotic E.-coli preparation (DSM17252) compared to placebo. Z Gastroenterol. 2009 Feb;47(2):209–14.
    18. Zhernakova A, Kurilshikov A, Bonder MJ, Tigchelaar EF, Schirmer M, Vatanen T, Mujagic Z, Vila AV, Falony G, Vieira-Silva S, Wang J, Imhann F, Brandsma E, Jankipersadsing SA, Joossens M, Cenit MC, Deelen P, Swertz MA; LifeLines cohort study, Weersma RK, Feskens EJ, Netea MG, Gevers D, Jonkers D, Franke L, Aulchenko YS, Huttenhower C, Raes J, Hofker MH, Xavier RJ, Wijmenga C, Fu J. Population-based metagenomics analysis reveals markers for gut microbiome composition and diversity. - Science. 2016 Apr 29;352(6285):565–9.