All About Gluten
What is gluten? And is it something you need to worry about?
Highlights
Individuals with celiac disease, wheat allergy, and gluten sensitivity experience adverse symptoms following ingestion of gluten containing foods.
Gluten is found in wheat, rye, and barley. Each of these grains can be eaten intact or as a processed flour found in baked goods and other recipes. When used in ultra-processed foods, gluten containing flours may be easier to overeat and thus lead to weight gain due to calorie excess. Weight gain as a confounding factor may aid in explaining gluten’s newfound poor reputation.
Gluten is found in many high FODMAP foods. After removing gluten from the diet, an individual may experience improved gastrointestinal tolerance due to a lower FODMAP diet. Thus, this individual may be experiencing symptoms of IBS rather than non-celiac gluten sensitivity.
For best tolerance of gluten (and other foods in general), keep your gut happy and healthy through a diet high in fiber and fermented foods.
Terms
Gluten: Gluten refers to the proteins found in wheat, rye, and barley. These proteins can be separated into two fractions based on their solubility: gliadins (soluble) and glutenins (insoluble). Gluten is known in baking for creating elasticity in dough, and is responsible for the spongy texture of your favorite artisanal sourdough bread.
Celiac disease: Celiac disease is an autoimmune disorder in which an individual has an adverse reaction to gluten. Symptoms of celiac disease (before eliminating gluten) include diarrhea, nutrient malabsorption, weight loss, and abdominal distention. In individuals with celiac disease, gluten, specifically gliadin peptides, permeate the epithelial barrier of the intestine and promote an inflammatory response. Repeated exposure to gluten proteins in these individuals can lead to intestinal tissue damage, thus a gluten-free diet is prescribed. Celiac disease is typically diagnosed by an intestinal biopsy that demonstrates the expected tissue damage–including increased presence of white blood cells, crypt hyperplasia (elongated grooves compared to a normal intestinal lining, and atrophy of intestinal villi)–and a positive response to a gluten-free diet.
Wheat allergy: Wheat allergy refers to immunologic responses to wheat, including skin, gastrointestinal, and/or respiratory reactions. Immunoglobulin E (IgE) antibodies play a crucial role in these reactions to wheat. It is important to note these IgE mediated responses are to wheat proteins–not necessarily isolated gluten proteins, though can include gluten.
Gluten sensitivity, or non-celiac gluten sensitivity: Gluten sensitivity includes adverse reactions to gluten not explained by celiac disease or wheat allergy. Gluten-sensitive individuals are not able to comfortably tolerate gluten, but gluten does not lead to intestinal damage, autoimmune response, or allergic reaction. Typically, gluten sensitivity is characterized by symptoms of gastrointestinal distress after eating gluten-containing foods, however, not accompanied by an autoimmune response or intestinal damage as seen in celiac disease. Gluten sensitivity is diagnosed by patient symptom reporting before and after a gluten elimination diet, including reintroduction of gluten post elimination. The understanding of this condition is in its nascent stage. In some cases, it may not be gluten causing the symptoms, but an affiliated compound.
Irritable bowel syndrome (IBS): IBS is defined by the presence of abdominal pain or discomfort and altered bowel habits, including loose stools, frequent stools, constipation, or bloating (in the absence of other diseases related to these symptoms). To differentiate from irritable bowel disease (defined below), a patient with IBS presents no abnormal physical differences in intestinal appearance during an exam.
Inflammatory bowel disease (IBD): IBD includes both Crohn’s disease and ulcerative colitis and is characterized by an abnormal mucosal immune response with physical damage to the gastrointestinal tract. Microbial factors and epithelial cell abnormalities can facilitate this inflammatory response. Crohn's patients typically report symptoms including abdominal pain, diarrhea, rectal bleeding, weight loss, fever, and fatigue and can develop a fistula in their gastrointestinal tract. In contrast, ulcerative colitis patients report similar symptoms, yet without fistula development, and only affecting the colon.
Microbiome: The human microbiome consists of the trillions of microbial cells harbored by individuals, residing anywhere from our skin to our guts. Although the microbiome field is fairly nascent, research suggests that differences in microbiome composition either play a role in disease onset or progression, or are another symptom of disease. For example, individuals with IBS have been shown to develop microbiome changes specific to both their primary IBS symptoms (constipation or diarrhea) and flare onset. Though we cannot draw clinical conclusions from these studies just yet, this emerging field may yield research in years to come to help explain and treat gastrointestinal diseases.
FODMAP: A low-FODMAP diet is a phased elimination and reintroduction diet used to treat IBS. FODMAPs–fermentable oligosaccharides, disaccharides, monosaccharides and polyols–can trigger flares in individuals with IBS. By systematically eliminating and re-introducing foods rich in FODMAPs, an individual and their dietitian can work towards reducing flare symptoms, identifying which foods trigger symptoms, and liberalizing diet with tweaks to minimize trigger foods. Foods that once triggered gastrointestinal symptoms may not always trigger symptoms, thus individuals (with the support of their dietitian) can re-introduce trigger foods in small doses at regular intervals to assess tolerance.
What is gluten, and what do gluten containing foods provide?
Gluten, as defined above, refers to proteins found in wheat, rye, and barley. Wheat, rye, and barley are grains eaten both intact and ground as flour in baked goods and other recipes.
Whole grains are part of a healthy diet, providing fiber, slow-digesting carbohydrates, and protein. Intact barley provides about 6 grams of fiber, 4 grams of protein, and 44 grams of carbohydrate per 1 cup cooked serving. Wheat and rye can also be eaten intact, often called wheat berries and rye berries at the grocery store. Choosing intact grains over ultra-processed foods with refined carbohydrates can help slow digestion and absorption of carbohydrates thus leading to a more stable blood sugar response.
Rye, wheat, and barley can also be processed into flour for use in baked goods. The processing of these intact grains removes some of the fiber, leading to a more rapid absorption. Each flour provides varying amounts of fiber per quarter cup (a typical serving) after processing: rye flour provides 3 grams, white wheat flour provides about 1 gram, and whole-grain wheat flour provides about 3 grams. Higher fiber flours can lead to slower absorption, thus a more stable blood sugar response, compared to the most abundant and lowest fiber option: white wheat flour.
That being said, you don’t need to completely eliminate foods made from processed flours. Pairing bread made from white flour with a source of fiber, protein, and fat can lead to a more satiating snack. For example, think sourdough toast with peanut butter and banana, or pita bread packed with turkey, hummus, and veggies.
The rapid rise in non-celiac gluten sensitivity poses the question: has wheat itself changed? Scientists characterized changes in wheat from 1891 to 2010 and found that wheat, as we know it today, has more glutenin fraction and less gliadin fraction, but no changes in gluten content overall. This finding suggests that gluten breeding has likely not led to increased reported gluten-intake related diseases, especially considering individuals with celiac disease respond to the gliadin fraction of gluten, which has decreased over the years.
How do we metabolize gluten?
Let’s break it down: when you eat a pasta dinner, how does gluten get from your plate to your intestine? Carbohydrate digestion begins in the mouth with the secretion of salivary amylase, an enzyme that breaks down the flour used to make your pasta. Some protein digestion begins in the stomach (remember, gluten refers to the proteins found in wheat), and if there has been enough breakdown in the mouth, hydrochloric acid and proteases (enzymes that break down proteins) will begin to digest some of the gluten proteins.
Once the remains of the pasta pass into the intestine, both carbohydrates and proteins are broken down by enzymes into their smallest components and absorbed through enterocytes–the cells that line the intestine. Gluten is thus broken down into single amino acids and small peptide chains before transportation across the intestinal lining into the bloodstream, where these amino acids are taken to tissues in need. Remember, protein is responsible for not only muscle synthesis, but the makeup of cells, signaling molecules, and other tissues to keep the body functioning day-to-day, so these amino acids can be taken anywhere in the body and used to create new proteins.
The microbiome also comes into play once gluten proteins reach the intestines. Incomplete digestion of gluten generates oligopeptides which are further digested by intestinal bacteria. Thus, gut microbiome composition and diversity affect gluten metabolism and gastrointestinal symptoms. General practices to induce microbiome diversity and gut health include eating enough fiber and fermented foods.
The connection between gluten and metabolic health
Gluten may get a bad rap due to its abundance in ultra-processed foods, which have been shown to be easier to overeat due to their hyperpalitability, thus can lead to weight gain due to calorie excess. Higher intake of whole grains or dietary fiber are associated with reduced disease incidence and mortality across many studies, indicating that increasing intake of whole grains and dietary fiber is important in disease prevention. Choosing intact grains, such as barley, wheat berries, and rye berries, and baked foods made with higher fiber flours such as whole-wheat and rye can increase fiber intake and aid in digestive and long term health.
Studies found individuals with celiac disease have increased intestinal inflammation and increased intestinal permeability following ingestion of gluten, whereas individuals with non-celiac gluten sensitivity do not express markers of inflammation in their intestinal mucosa or experience significantly increased intestinal permeability. A small study found that individuals with IBS may have increased small intestine permeability after gluten ingestion. Previous studies have shown that gliadin, a fraction of gluten, leads to transient increase in gut permeability in all individuals. However, it is important to note that many compounds lead to temporary intestinal permeability, and that these studies look at biopsies of intestinal cells cultured outside the body. So although the data can give us further hypotheses to work from, we cannot make clinical conclusions from these studies. Specific indigestible gliadin fragments also bind to a receptor to signal subsequent release of zonulin, a protein that modulates intercellular tight junctions, which affect intestinal permeability. For the majority of people eating gluten, these events do not lead to abnormal consequences. However, in people with celiac disease, these same events can lead to an inflammatory process when gluten is mistakenly recognized as a pathogen.
The intestinal epithelium forms a semi-permeable barrier that allows the absorption of nutrients, electrolytes, and water, but protects from microbiota and unwanted molecules in the gut lumen. This mucosal barrier provides protection against the absorption of unwanted compounds across the intestine into the bloodstream. A compromised intestinal barrier is associated with an array of clinical conditions, yet it remains unclear if increased permeability alone is a casual or strong contributing factor in the disease. Dietary interventions that reinforce the intestinal barrier have been shown in animal models, but the relevance of these studies to human health remains unknown. Some hypothesize that lower-fiber diets of modern times lead to different microbiomes than our ancestors, and since our microbiomes work hand-in-hand with the intestinal mucosal membrane, leads to the belief that these lower fiber diets may be leading to perturbed intestinal habitat. This area of research is in its nascent phase in humans, and will be exciting to follow.
Gluten and IBS/IBD?
For individuals with IBS, a low-FODMAP diet may help alleviate gastrointestinal symptoms during a flare. Foods rich in FODMAPs include wheat and rye, thus an individual with IBS would likely benefit from a gluten-free diet during a flare if this is one of their trigger foods, not necessarily because of the gluten elimination, but because by proxy this diet would be low in the FODMAPs found in wheat and rye. A low-FODMAP diet is not meant to be a lifetime diet. Individuals with IBS should work with a dietitian to first eliminate foods rich in FODMAPs from their diets, then systematically re-introduce foods rich in FODMAPs to identify trigger foods. An individual with IBS and their dietitian can work towards reducing flare symptoms, identifying which foods trigger symptoms, and liberalizing diet with tweaks to minimize trigger foods. Foods that once triggered gastrointestinal symptoms may not always trigger symptoms, thus individuals (with the support of their dietitian) can re-introduce trigger foods in small doses at regular intervals to assess tolerance. An individual with IBS that once did not tolerate gluten may come to tolerate gluten after a flare, or later on.
In the case of IBD, medication is the first line of management and response to dietary intervention is variable. A low-FODMAP diet may aid in symptom management, however, the risk of developing malnutrition is high and an elimination diet can worsen risk, thus is not the first line of defense and, if desired, should be overseen by a doctor or dietitian.
What should you do?
Continue to enjoy gluten guilt free. The majority of people are able to digest gluten, and whole grain products can increase dietary fiber, complex carbohydrate, and protein intake, all important parts of a healthy diet.
Choose intact grains and higher fiber flours for a fiber boost. Intact grains are the most nutritionally dense and provide more fiber than their processed counterparts. Second best are higher-fiber flours, such as whole-wheat and rye.
Assess gluten sensitivity with the help of a clinician. A doctor or dietitian trained in gastrointestinal health can help you assess if gluten is something you need to avoid.
Eat a diet that will keep your gut happy. Whole grains, fruits, and vegetables provide not only micronutrients, but fiber that will keep your gut happy. Fermented foods may also aid in promoting intestinal microbiome diversity.
