The majority of my patients come to me already with some vague knowledge about gluten-free (GF) foods. However, many do not know what gluten is or why GF items have been inserted into menus everywhere. I often spend time explaining how gluten causes disease in Celiac disease (CD) patients and why non-celiac disease patients feel better when they stop eating gluten. This conversation often leads further into a discussion of the difference between food allergy and food intolerance. The main misconception I have seen is that many patients without CD feel they have a food allergy when in fact they have a food intolerance.
What is gluten?
Gluten is not that mysterious. It is a collection of proteins that are found in wheat, barley, and rye. Gluten is important clinically as it is the main cause of CD. An individual with CD needs to completely avoid Gluten in order to heal from the disease. CD is an autoimmune disease. Autoimmune diseases are characterized by an inappropriate activation of the immune system. Self or endogenous antigens (markers of self) are 'perceived' as foreign. Once activated, the immune system leads to the destruction of the absorptive surface of the small intestine.
CD is common, found in approximately 1% of the population. I typically tell patients that it is less common than irritable bowel syndrome (1 out of 7), but more common than Crohn's disease (1 out of 500-1000 patients).
If it's only 1% of the population, why are gluten-free foods so ubiquitous? Well, certainly CD patients should be afforded the same rights to eat as safely as non-celiac patients. However, many people without celiac disease have found that removing gluten from their diets makes them feel less full, less bloated, and less fatigued. Clinically, this has been called non-celiac gluten sensitivity (NCGS). It is not clear if there is a distinct biological entity that results in pathological changes other than those seen in CD.
If these patients are ill but do not have CD, why do they feel better when they remove gluten? What is more likely happening is that people are responding to the removal of something from their diet that gluten is associated with, rather than the gluten itself. This has actually been shown in a clinical study. My bet is that these patients are responding to the FODMAPs found in foods made with wheat, rye, and barley.
What are FODMAPS?
Fermentable Oligosaccharides Disaccharides Monosaccharides and Polyols. These are all forms of carbohydrates or sugars in varying shapes and sizes that are poorly absorbed or not well digested. FODMAPs are fermented in the colon by bacteria which results in the production of hydrogen gas (flatus, bloating, abdominal distention, pain), short chain fatty acids, and causes an osmotic effect to draw in water to the stool (diarrhea).
If you or someone you know has responded to a Gluten-free diet make sure they see a gastroenterologist to learn whether they in fact have an intolerance to foods containing gluten or have CD. CD can be tested by obtaining measurements of circulating antibody markers. Those that have excluded all gluten from their diet will need to be re-challenged with it for 6 weeks with at least 1-2 slices of bread a day. This is because patients with CD lose the diagnostic serum markers of the disease while on a gluten-free diet. If markers are positive, confirmation will be needed by obtaining small intestine biopsies during an upper endoscopy.
What markers are most sensitive and specific? In the presence of normal serum IgA levels, I have found that the IgA anti-tissue transglutaminase antibody is most sensitive and specific. Others tend to have low positive predictive values.
Is there a genetic test? Yes and no. The test is only useful to exclude celiac disease. I utilize HLA DQ2/DQ8 allele testing when results of testing are ambiguous, or their is a high suspicion despite conflicting test results (i.e. positive markers, negative biopsy). A positive test (presence of both alleles) is seen in 99.9% of CD patients while only 40-50% of the general population tests positive. Thus, a positive value does not diagnose CD. Rather, it is the absence of these alleles (negative result) that excludes CD.