Summary: The past few years have seen an explosion of consciousness in our culture surrounding the protein gluten found in food products made from wheat, barley, and rye. While celiac disease, an immune-modulated disease that is triggered by gluten, is well understood, a new clinical entity titled non-celiac gluten sensitivity (NCGS) has become prominent in the medical literature. Despite the availability of a mouse model, as well as interesting in vitro studies using tissue samples from patients that suggest putative mechanisms for NCGS, it is unclear whether this sensitivity is even real. A recent study noted that gluten had no symptomatic effects in a cohort of patients that had previously been described as NCGS when the researchers controlled for the effects of short, fermentable carbohydrates that also exist at high levels in wheat-derived foods. In light of this evidence, it appears that the vast majority of patients described as having NCGS are actually suffering from a reaction to these FODMAP carbohydrates. This finding gives new possibilities to those patients who have eliminated gluten from their diets, but still suffer from irritable bowel syndrome-like symptoms.
Gluten: A storage protein of wheat, barley, and rye. Consists of two polypeptides (amino acid chains): glutenin and gliadin
Leukocyte: Also known as white blood cells. These are any of a number of classes of cells deriving from bone marrow that operate within the immune system
Villi: Cellular microstructures found in the intestine responsible for absorbing nutrients from digested food
Peptide: Short chain of amino acids
T-cell: One class of leukocytes. Involved in cell-mediated immunity
Cytokine: Intercellular chemical signal
Irritable Bowel Syndrome: Some or all of a collection of bowel symptoms including abdominal pain, bloating, diarrhea, and constipation.
GS: Gluten sensitivity
NCGS: Non-celiac gluten sensitivity
IBS: Irritable bowel syndrome
IL: Intraepithelial leukocytosis
TTG: Transtissue glutaminase
FODMAP: Fermentable oligo-, di-, mono-saccharides and polyols
NSAID: Non-steroid anti-inflammatory drug
T1D: Type 1 diabetes
Gluten-free foods are big business here in the US. A recent report put the market at over $10 billion in 2013, and it’s growing rapidly.(1) For the approximately 1% of Americans with celiac disease, this newfound variety at the supermarket and the bevy of restaurants catering to their needs must be a huge relief and an immeasurable improvement over a lifetime of scrutinizing labels and annoying wait staff with a 21 Questions routine. Yet, it’s not just celiac disease that drives the growth of this market. I’m sure we all have a friend who has convinced him- or herself of a self-diagnosis of gluten intolerance, gluten sensitivity, or some other vaguely defined malady for which the latter-day demon of wheat protein is responsible. With all the media attention that gluten has attracted in the past few years, this isn’t shocking. In the internet age, sometimes we simply have too much information on our hands, and too few tools to determine which of it is valid. For anyone without access to scientific journals and a few days of free time on their hands to separate the wheat from the chaff, prudence may be the best option. However, if a “better safe than sorry” approach involves eliminating pizza and beer from your life, then safe IS sorry.
In order to determine the common perceptions of gluten I simply plugged “gluten sensitivity” into Google to see what popped up. Aside from the celiac disease-specific websites, there were also a number of hits from widely read media sources. The Huffington Post, Forbes, The Atlantic, Scientific American, and NPR have all promoted stories on the subject. What struck me in particular was the alarmist language used in some of these articles. The HuffPost article in particular, titled “Gluten: What you don’t know might kill you”(2), reads like a scandal exposé with hyperbolic language and a seemingly unending list of symptoms attributed to gluten intake. Unsurprisingly, at the end of the article, the author hawked his line of nutrition books.(3)
If the first rule of being an informed consumer is to be skeptical of information coming from a source with a profit motive, then we need to look elsewhere for trustworthy information. The other articles were more nuanced, and the more recent ones included a study linking short, fermentable carbohydrates to GI symptoms (much more on this later). However, when it comes to dietary prescriptions, journalists generally throw their hands up and say, “It’s complicated,” which is probably for the best coming from non-medical sources.
So, what is the current state of the science surrounding celiac disease and gluten intolerance, and how can we use that information to live as healthily as possible while still enjoying our food culture to the maximum?
Celiac disease is a precisely defined entity characterized by “chronic inflammation of the proximal small intestine resulting in villous atrophy and malabsorption that can develop in genetically susceptible individuals ingesting gluten, the storage proteins of wheat, barley, and rye.”(4) There is not a complete consensus in the medical community as to the precise definition of non-celiac gluten sensitivity (NCGS), also sometimes referred to as gluten-sensitive irritable bowl syndrome. However, it is generally accepted to be some set of gastrointestinal symptoms that falls short of a full diagnosis of celiac disease, but that still responds positively to a gluten-free diet. The mechanisms of pathology in celiac disease have been extensively studied, and by examining biological processes that lead to celiac disease in patients exhibiting NCGS, medical scientists have made progress in understanding this condition.
Virtually all celiac disease patients, and many of those reporting NCGS, carry one of two alleles (gene variants) called HLA-DQ2 and HLA-DQ8. This is a gene involved in presenting foreign substances to T-cells to raise an immune response. Proper functioning of these genes early in life allows the body to distinguish itself from foreign agents; hence, harmful variants of the normally helpful HLA-DQ genes are often involved in auto-immune disorders. These two particular alleles have an elevated affinity for a peptide that is a digestion product of gliadin, one of the proteins that make up gluten, and activate the immune system when presented with this gliadin digest. In celiac disease patients, this causes the production of antibodies directed at gliadin, infiltration of lymphocytes (white blood cells) into the intestine, and ultimately destruction of the villi (cellular microstructures in the intestine that absorb nutrients) and a breakdown of tight junctions between the epithelial cells of the intestine.
So what, if any of this, is replicated in people experiencing NCGS? Unfortunately, there is a tremendous amount of variability in the patient population, making it hard to pin down the causative agents. In one study(5), 12 of 28 patients with intraepithelial lymphocytosis (IL) were classified as gluten-sensitive based on response to a gluten-free diet, consistent with other studies(6,7) that place less than 50% of those with IL on the GS spectrum. Still more studies have shown the presence of anti-gliadin and anti-trans-tissue glutaminase (an enzyme involved in the processing of gliadin) antibodies in the absence of IL.(8,9) So, in symptomatic gluten-sensitive patients ,it’s possible to present either of the two proximal causes of gluten-sensitive symptoms without the other cause.
An important distinction to make here is between local immune response and systemic immune response. In the studies just mentioned, antibodies were found in the intestine. However, in addition to GI symptoms, many patients report peripheral symptoms like fatigue and headaches. Celiac disease patients, due to the breakdown of the intestinal barrier, do not only have an immune response in the gut, but also have antibodies circulating in their blood. This barrier breakdown introduces activated immune components from the intestine into the bloodstream, and it also allows otherwise healthy (when contained in the gut) bacteria to enter into circulation and cause offsite immune system activity. While initially researching this subject, I thought that these particular effects would be limited to celiac patients due to the lack of villous atrophy in NCGS; however, I later found a study(10) showing that non-celiac intestinal tissue also becomes more permeable in response to gliadin, albeit transiently and to a lesser extent than does celiac tissue. Therefore, it is possible that non-celiac patients also have circulating antibodies and gliadin digestion peptides. A pro-inflammatory immune response to these circulating elements could be the source of the non-GI symptoms experienced by some patients, as evidenced by studies of leukocyte activation on stimulation with gliadin.(11)
Neuronal signaling is another proposed mechanism by which NCGS might cause GI tract pathology.(12) Dysregulation of neuronal signaling molecules such as serotonin and acetylcholine has been shown in other conditions associated with GI inflammation. The nerves controlling the smooth muscles that move food through the digestive system are regulated by these signaling molecules. An imbalance in neuronal signaling could therefore cause food to either move through the gut too quickly, or to linger in the gut for too long, contributing to GI symptoms.
Finally, psychological factors must be considered. One study examined the effect of removing nutrients from the diet of people who had circulating antibodies to those nutrients.(13) The patients showed only a 10% greater reduction in symptoms when on the real diet as opposed to a sham diet, showing a strong placebo effect in the sham diet. In this study, reintroduction of the food worsened symptoms in 83% of those on the real diet, suggesting that immune response to certain food chemicals has symptomatic effects, but symptoms also worsened in 31% of patients receiving the sham diet, indicating that the placebo effect was also contributing.
This heterogeneity of biological markers in patients presenting NCGS leads to its working definition as a condition in which some of the markers of celiac disease are present, but villous atrophy is not. In many of these studies, healthy controls showed the same immune markers as did symptomatic patients (though less frequently); additionally, different patients reporting the same symptoms can present some, but not all, of the aforementioned immune responses. This led me to wonder, are all of these disease markers just red herrings? Alternatively, perhaps all of these biological processes contribute to the pathology, but none of them is sufficient on its own.
The diversity of biological processes that are significantly – yet weakly – affected by gluten intake suggests that there may be some threshold of a combination of these effects that must be crossed before symptoms become apparent. This combinatorial hypothesis is backed up by studies in transgenic mice expressing human HLA-DQ8 as well as an adaptor molecule that allows the mouse immune system to interact with human HLA.(11,12) These mice showed increased T-cell proliferation and increased acetylcholine release upon gliadin presentation, yet they did not show any villous atrophy. This suggests that additional underlying factors contribute to pathology in genetically susceptible individuals.
I found an article by Verdu, Armstrong, and Murray in the American Journal of Gastroenterology titled “Between Celiac and Irritable Bowel Sydrome: a No-Man’s Land of Gluten Sensitivity”(4) to be indispensible in compiling the research that has been presented thus far. However, this article appeared in 2009, prior to work from Peter Gibson’s lab at Monash University in Melbourne showing that patients self-reporting NCGS have no symptomatic response to gluten when researchers control for the presence of FODMAPs.(14)
FODMAP is an acronym for fermentable oligo-, di-, mono-saccharides, and polyols. These are short-chain sugars and sugar alcohols that are poorly absorbed in the small intestine and can be fermented by gut bacteria. In this very thorough study, the researchers assessed subjective symptoms such as pain, bloating, satisfaction with stool consistency, and fatigue with daily questionnaires, and also tracked the daily activity and sleep of participants with accelerometers, and measured levels of circulating antibodies. Additionally, they collected fecal samples to measure the pH and mass of feces, and to check for markers of intestinal inflammation.
In this study they saw an improvement of GI symptoms after an initial period on a gluten-free, low FODMAP diet with 22% of patients reporting over a 20 point improvement overall on a 100 point scale. At the end of the run-in participants were either placed on a low-gluten diet, a high-gluten diet, or a placebo diet including whey protein. Each participant underwent each arm of the study to act as internal controls. Overall symptoms and pain increased regardless of diet. Interestingly, bloating and tiredness increased only in the placebo and low-gluten arms of the study, suggesting a strong nocebo effect. Gluten specific symptomatic response was seen in only 3 subjects, (8%) of participants. Interestingly, 11 participants (30%) showed symptomatic increase in the placebo arm. Of those 8 showed a response to low gluten, only 1 responded to the high gluten arm.
After the initial study, participants were invited back to participate in a rechallenge. The two participants who reported a response to high gluten arm in the initial trial showed no response in the retrial, however, two subjects who had not reported symptoms on the original gluten trial reported symptoms on retrial.(15) Of the three subjects who reported symptomatic response to whey in the first trial, one continued to experience whey specific symptoms in the retrial. The main take away from these experiments is that the predominant bowel habits, body mass index, age, sex, duration of GF diet, and, importantly, HLA-DQ status did not predict response to any of the diets. In both trial and retrial, the only thing that correlated to severity of symptoms was the order in which the diets were administered. Subjects showed a greater symptomatic response to the first diet they were put on than the subsequent ones, regardless of what each diet contained.
These results carried through to the other measurements taken during the study. Fatigue scores improved during the run-in period compared to base line, and then became worse during the diet trials, however, no difference was seen between the three arms of the trial. Similarly, there were no effects of dietary treatment on activity levels or quality of sleep as measured by accelerometer. Only one subject showed a positive T-cell response following high gluten arm, and that response was similar to those elicited in celiac patients. There were no significant differences across diet arms for circulating antibodies or fecal biomarkers, and there was no correlation between symptomatic response to the high gluten arm and any of the biomarkers measured. Nor were there correlations between the biomarker response to high gluten diet and HLA status.
In light of this study, what can we say about relationship between gluten and IBS-like symptoms? Certainly previous studies looking at wheat intake in patients must be reinterpreted in light of FODMAP restriction that would accompany a gluten free diet. Any studies showing a gluten response that did not control for FODMAPs were likely registering symptoms due to FODMAP consumption. However, we cannot entirely rule out a biological response to gluten, especially in HLA-DQ2 and HLA-DQ8 positive individuals. The FODMAP controlled study had a somewhat small sample size, and does not attempt to make comprehensive conclusions about all IBS patients. The in-vitro studies mostly used purified gluten or gliadin in the absence of other components of wheat, and still show a phenotypic response. Mapping experiments have show exactly which gliadin digest peptide is implicated in eliciting these responses, so the mechanism is fairly well understood. So why do we see gluten specific responses in in-vitro and ex-vivo studies, but not in patient cohorts? It is likely due to the fact that these experiments look at cells in very specific contexts involving priming with cytokines, and pro-inflammatory molecular milieus, and in the absence of compensating pathways that would exist in-vivo. The fact that not all genetically susceptible individuals develop celiac disease, and that many of these gliadin studies show an effect that, while significant, is somewhat weak suggests that the pathologies underling gluten sensitivity are multi-factorial and combinatorial. Some combination of immune activation/disregulation, gut barrier break down, microbiome composition, and antigen concentration has to be present for symptoms to develop.
So how can we apply this information to our lives? It appears that the majority of previously describe NCGS is actually a digestive reaction to FODMAPs. If you found a gluten free diet reduces your symptoms, but does not eliminate them, you are probably reacting to FODMAPs, and a trial period with a low FODMAP diet is advisable. Keep in mind that our digestive enzyme expression, and the composition of our microbiome change in response to our diets. If you’re planning on a drastic dietary change, you should ease your way into it, and wait at least a week on the new diet to assess any changes you might be experiencing.
The data out of the Gibson lab suggest that adding in a component that your body has trouble with will produce symptoms within three days, however, removing harmful elements may not show improvements for over a week as your body eliminates the last trace amounts and adjusts to a new diet. As always when entering a restriction diet it’ll take a bit of work to make sure you take in a full compliment of micronutrients and don’t skimp on fiber. There are numerous resources online to help you with this. If you’re an otherwise healthy individual who was worrying about gluten intake because of the litany of scare pieces that have appeared in the media, you can feel safe letting those fears subside. In fact, it might be counter-productive to embark on a gluten free diet in a non-gluten sensitive individual, as at least one study has linked gluten free diets with a decrease in gut bacteria that can protect against inflammation and intestinal damage. However, in healthy individuals it might not be a bad idea to limit gluten and FODMAP intake when there is an acute stress to the GI tract such as an infection or an extended period of NSAID use.
There are rare, but notable exceptions to this dietary advice. A recent study using mouse and rat models of type-1 diabetes showed increased autoimmune activity targeted toward insulin secreting pancreas cells when incubated with gliadin digest, suggesting that a gluten free diet may help mitigate T1D in patients with gluten reactive HLA types. Additionally, a recent study from Spain showed symptom remission in 20 fibromyalgia patients placed on a gluten free diet, however they did not control for FODMAP intake, and the patient cohort is rather small due to the specificity of the screening to participate in this study. If you are experiencing anything more than sporadic mild symptoms, or have any underlying medical conditions, seek out a physician to help with dietary planning.
The growing body of research in this field is extremely helpful to clinicians trying to help patients deal with chronic bowel issues. Increasing knowledge of potential triggers is allowing both health care professionals and individuals to manage their diets in such a way as to minimize symptoms. Obviously, in a system as complex as human digestion, it is hard to truly evaluate the effects any one input when there is so much heterogeneity in genetic backgrounds and other environmental factors within the patient population.
It’s heartening to see researchers attacking this issue at all levels, from precise protein mapping and cell culture experiments, to dietary manipulation in large study cohorts. Although, some seemingly inconsistent results from the patient studies and the mechanistic studies show that there is more work to be done to understand these conditions. Particularly active areas of research that may contribute more to our understanding of these diseases are looking at the gut microbiome, and specifically the gut-brain axis, as well as cellular and systemic responses to chronic inflammation. Combining the specifics known about gluten and FODMAP intake with further advances in these more general fields should lead to some interesting new hypotheses about what is contributing to IBS, and how to better manage our bodies in order to live more healthily. That’s something I’m really looking forward to, especially if there’s a way to accomplish this while indulging in pizza and beer.
1) Strom, S. (2014, February 17). A Big Bet on Gluten-Free. The New York Times. Retrieved from http://www.nytimes.com/2014/02/18/business/food-industry-wagers-big-on-gluten-free.html?_r=1
2) Hyman, M. (2011, November 17). Gluten: What you don’t know might kill you. The Huffington Post. Retrieved from http://www.huffingtonpost.com/dr-mark-hyman/gluten-what-you-dont-know_b_379089.html
3) In fairness, this article was written in 2010, prior to two important studies that will be discussed later in this article, when the science available was much less conclusive. Although, it hasn’t been updated since November, 2011 despite the author keeping up a very active contribution to HuffPost to this day.
4) Verdu, E., Armstrong, D., & Murray, J. Between Celiac Disease and Irritable Bowel Syndrome: The “No Man’s Land” of Gluten Sensitivity. Am J Gastroenterol. 2009 June; 104(6): 1587–1594.
5) Mino M, Lauwers GY. Role of lymphocytic immunophenotyping in the diagnosis of gluten-sensitive enteropathy with preserved villous architecture. Am J Surg Pathol. 2003; 27:1237–42.
6) Kakar S, Nehra V, Murray JA, et al. Significance of intraepithelial lymphocytosis in small bowel biopsy samples with normal mucosal architecture. AJG. 2003; 98:2027–33.
7) Vande Voort JL, Murray JA, Lahr BD, et al. Lymphocytic duodenosis and the spectrum of celiac disease. Am J Gastroenterol. 2009; 104:142–8.
8) O’Mahony S, Vestey JP, Ferguson A. Similarities in intestinal humoral immunity in dermatitis herpetiformis without enteropathy and in coeliac disease. Lancet. 1990; 335:1487–90.
9) Salmi TT, Collin P, Jarvinen O, et al. Immunoglobulin A autoantibodies against transglutaminase 2 in the small intestinal mucosa predict forthcoming coeliac disease. Aliment Pharmacol Ther. 2006; 24:541–52.
10) Drago, S. et al. Gliadin, zonulin and gut permeability: Effects on celiac and non-celiac intestinal mucosa and intestinal cell lines. Scandinavian Journal of Gastroenterology. 2006; 41:408-419.
11) Black KE, Murray JA, David CS. HLA-DQ determines the response to exogenous wheat proteins: a model of gluten sensitivity in transgenic knockout mice. J Immunol. 2002; 169:5595–600.
12) Verdu, EF, et al. Gliadin-dependent neuromuscular and epithelial secretory responses in gluten-sensitive HLA-DQ8 transgenic mice. Am J Physiol Gastrointest Liver Physiol. 2008 Jan; 294(1): G217-25.
13) Shanahan F, Whorwell PJ. IgG-mediated food intolerance in irritable bowel syndrome: a real phenomenon or an epiphenomenom? Am J Gastroenterol. 2005; 100:1558–9.
14) Biesiekierski, JR, et al. No Effects of Gluten in Patients With Self-Reported Non-Celiac Gluten Sensitivity After Dietary Reduction of Fermentable, Poorly Absorbed, Short-Chain Carbohydrates. Gastroenterology 2013; 145: 320–328.
15) The numbers for the rechallenge trial are smaller because not all of the original study subjects participated in the rechallenge.