Celiac disease is a chronic autoimmune condition where ingesting gluten (a protein found in wheat, barley, and rye) triggers an immune response. This reaction causes inflammation and damage within the small intestine, the primary site for nutrient and fluid absorption. Chronic diarrhea is one of the most common symptoms that prompts individuals to seek medical evaluation. Understanding how this autoimmune reaction causes digestive distress is key to effective management.
The Mechanism of Diarrhea
The body’s immune system mistakenly targets the lining of the small intestine when gluten is consumed, causing villous atrophy. Villi are tiny, finger-like projections that line the small intestine, increasing the surface area for absorbing nutrients and water. When these villi are damaged and flattened, this surface area is severely reduced, which is the root cause of malabsorption.
This structural damage impairs the digestive process, meaning fats, carbohydrates, and proteins are not properly taken up. These unabsorbed components progress into the colon, drawing excess water into the bowel through osmosis. This osmotic effect results in large volumes of watery or loose stool, manifesting as malabsorptive diarrhea.
Unabsorbed nutrients become food for bacteria residing in the colon. Bacterial fermentation produces gases and byproducts, including specific hydroxy fatty acids. These fatty acids irritate the colon lining and stimulate the secretion of more fluid and electrolytes. The combination of reduced absorption, osmotic water retention, and increased fluid secretion leads to the characteristic chronic diarrhea.
Identifying Celiac-Related Diarrhea
The diarrhea linked to celiac disease often has distinct characteristics due to fat malabsorption. This specific type of stool, known as steatorrhea, is typically pale, bulky, and foul-smelling. The light tan color results from the presence of unabsorbed fat.
Steatorrhea may also appear greasy or oily, and patients often notice that the stools are difficult to flush or tend to float. This appearance is a direct consequence of damaged villi failing to absorb dietary fat, which is then excreted. Steatorrhea’s greasy, bulky quality makes it a distinguishing feature of chronic malabsorption caused by celiac disease.
Confirming the Cause
Confirming celiac disease as the cause of chronic diarrhea begins with specific blood tests known as serology. These tests screen for antibodies the immune system produces in response to gluten, most commonly the tissue transglutaminase IgA (tTG-IgA) antibody. A positive blood test indicates a high likelihood of the condition.
Definitive confirmation requires an upper endoscopy with a small intestine biopsy. A gastroenterologist collects tiny tissue samples to visually confirm the presence of villous atrophy, the physical evidence of intestinal damage. Patients must continue eating a gluten-containing diet throughout testing, as removing gluten prematurely can cause the villi to heal, leading to false-negative results.
Stopping the Diarrhea
The most effective way to resolve chronic diarrhea is strict, lifelong adherence to a Gluten-Free Diet (GFD). Eliminating all sources of gluten halts the immune reaction, allowing the damaged small intestinal villi to begin healing. As the villi recover their structure, the small intestine’s capacity to absorb water and nutrients is restored, stopping the malabsorption.
Many patients report a noticeable decrease in digestive symptoms within a few days to a few weeks of starting the GFD. However, physical healing of the intestinal lining takes considerably longer, often requiring months to fully regenerate the villi. Adults may take six months to two years to achieve complete mucosal recovery. If chronic diarrhea persists despite strict adherence, it may signal non-responsive celiac disease, requiring medical re-evaluation for issues like microscopic colitis or persistent gluten exposure.