Celiac Disease Symptoms: What Gluten Actually Does to Your Body

Celiac disease is not a food intolerance. It is not an allergy. It is an autoimmune disease where eating gluten - a protein in wheat, barley, and rye - causes your own immune system to attack the lining of your small intestine. About 1 in 141 Americans has it, and the majority do not know. Estimates put the undiagnosed rate somewhere between 50% and 83%.

The reason it stays hidden is that classic "sick after eating bread" symptoms are the exception in adults, not the rule. The symptoms are often subtle, chronic, and easy to blame on something else: iron deficiency, an itchy rash, a bad back, brain fog, an unexplained miscarriage. This piece covers what celiac disease actually does to the body, why adults get missed for years, and what to test for before going gluten-free.

What Celiac Disease Actually Is

When someone with celiac disease eats gluten, their immune system produces antibodies against an enzyme in the intestinal lining called tissue transglutaminase (tTG). Those antibodies flatten the tiny finger-like projections called villi that line the small intestine. Villi are where you absorb nutrients. Damage them, and you stop absorbing iron, calcium, folate, B12, and fat-soluble vitamins - regardless of how well you eat.

That is why celiac symptoms rarely stay in the gut. The disease is an autoimmune process that starts in the intestine and cascades through the body. The New England Journal of Medicine now describes it as a systemic autoimmune disorder with intestinal manifestations, not a GI disease with occasional extra features.

Two things have to be true for celiac disease to develop: you need the genetic setup (almost all patients carry the HLA-DQ2 or HLA-DQ8 gene variant) and you need exposure to gluten. The genes alone are not enough - about 30% of the general population has them, and only a small fraction ever develops the disease.

The Classic Digestive Symptoms

When celiac does present in the gut, the pattern is fairly consistent. The Celiac Disease Foundation lists these as the most common GI complaints:

• Chronic diarrhea - loose, sometimes pale, greasy, and foul-smelling. This is steatorrhea, a sign that fat is not being absorbed. The Bristol Stool Chart typically shows Type 5 to 7 stools most days.
• Constipation - counterintuitive but common. About one in three adult celiac patients presents with constipation, not diarrhea.
• Bloating and abdominal distension after meals, particularly gluten-containing ones.
• Cramping and abdominal pain, often mistaken for IBS for years.
• Excessive gas from undigested carbohydrates fermenting in the gut.
• Nausea and occasional vomiting, especially after larger gluten meals.
• Unintended weight loss, though weight gain is also possible when fluid retention masks nutrient loss.

Yellow, floating stool that persists is a particularly useful signal because it suggests fat malabsorption - a hallmark of intestinal damage. If that pattern is present most days, our guide on yellow stool causes covers when steatorrhea points to celiac versus other malabsorption conditions.

Why Adults Get Missed

Here is the trap: adult celiac disease often does not look like a gut problem. A U.S. claims-database study found the average delay from first medical visit to diagnosis was about three years, and a prospective nationwide study put the delay from first symptoms at 9.7 years on average. Ten years of blood work, specialists, and gluten while the intestine kept getting flatter.

Two shifts explain this. First, the presentation in adults is heavily "atypical" - fewer digestive complaints, more silent extraintestinal signs. Second, primary care physicians order celiac screening far less often than the guidelines recommend, particularly when the patient does not have classic diarrhea. A 2025 review noted diagnostic delays are worse for women (median 21.8 months vs 16.8 for men), Hispanic and Black patients (about three years), and adults over 60.

Extraintestinal Symptoms: The Hidden Presentation

The symptoms that eventually flag celiac disease in an adult are often nowhere near the intestine. This is the list every primary care physician should have memorized and does not.

Iron-deficiency anemia

Present in roughly 40% of adult celiac cases and often the only symptom that shows up on routine labs. Damaged villi cannot absorb iron efficiently, so oral iron supplements fail to correct the deficiency. Any adult with iron-deficiency anemia that does not respond to iron therapy should be screened for celiac disease before further workup.

Dermatitis herpetiformis

An intensely itchy, blistering rash that clusters on the elbows, knees, buttocks, back, or scalp. It is pathognomonic for celiac - meaning if you have it, you have celiac, full stop, even without gut symptoms. It affects 10% to 25% of people with celiac disease. The rash responds to a gluten-free diet.

Bone loss and unexplained fractures

Impaired calcium and vitamin D absorption leads to low bone density. Adults with untreated celiac disease can develop osteopenia or osteoporosis decades earlier than expected. The rate is roughly double in patients with delayed diagnosis compared to those diagnosed early.

Neurological symptoms

Peripheral neuropathy (numbness and tingling in hands and feet), chronic migraine, ataxia, and "brain fog" - the difficulty concentrating that many patients describe as their most disabling symptom. The mechanism involves both nutrient deficiencies (B12, folate) and direct antibody effects on the nervous system.

Reproductive issues

Recurrent miscarriage, unexplained infertility, delayed menarche, and early menopause show up at higher rates in undiagnosed celiac. The risk of infertility in patients with delayed diagnosis is roughly double that of promptly diagnosed patients.

Elevated liver enzymes

Unexplained elevations of ALT and AST show up in some undiagnosed adults. Celiac hepatitis usually resolves on a gluten-free diet.

Mouth and dental signs

Recurrent aphthous ulcers (mouth ulcers) and enamel defects on adult teeth from childhood malabsorption.

Mood changes

Depression and anxiety appear more frequently in undiagnosed celiac patients and often improve significantly after a year on a gluten-free diet.

Celiac vs Gluten Sensitivity vs Wheat Allergy

These three conditions all cause reactions to wheat, but the mechanisms and the stakes are completely different.

Celiac disease is autoimmune. The trigger is gluten. Even 20 parts per million can activate the immune response and damage the intestinal lining. There is no cheat day. Treatment is a strict, lifelong gluten-free diet with no tolerance for cross-contamination.

Non-celiac gluten sensitivity (NCGS) causes symptoms similar to celiac (bloating, brain fog, headaches, fatigue, loose stools) but produces no antibody response and no intestinal damage. It affects an estimated 6% of the U.S. population, though the mechanism is still poorly understood. Some researchers think FODMAP fructans, not gluten itself, drive many of these cases - which is why our low-FODMAP diet guide often helps people who assumed they had a gluten problem.

Wheat allergy is a true IgE-mediated allergy. Reactions are fast (minutes to hours), can include hives, wheezing, and anaphylaxis, and are triggered by any wheat protein, not specifically gluten. About two-thirds of children with wheat allergy outgrow it by age 12. Adult-onset wheat allergy is rare.

The overlap creates a diagnostic mess. People with vague digestive symptoms try a gluten-free diet, feel better, and assume they have a gluten problem. If they never got tested first, they may have missed a celiac diagnosis. Getting the label right matters because the treatment intensity differs and the long-term risks differ.

How Celiac Disease Is Diagnosed

The diagnostic workup has two required stages. Both depend on the patient continuing to eat gluten. Cutting gluten before testing will normalize the antibodies and heal the intestine enough to produce false negatives.

Step 1: Blood tests

The first-line screen is the tissue transglutaminase IgA antibody test (tTG-IgA). It has excellent performance: sensitivity over 90% and specificity over 95%. A total IgA level is measured alongside it because 2 to 3% of celiac patients have selective IgA deficiency, which would produce a false negative on the primary test.

Endomysial antibodies (EMA-IgA) and deamidated gliadin peptide antibodies (DGP-IgG) are used as confirmatory tests or when IgA deficiency is present. HLA-DQ2/DQ8 genetic testing is not a diagnostic test - it is a rule-out. If both genes are absent, celiac is essentially impossible. If either is present, it only means you could develop it, not that you have it.

Step 2: Endoscopy with duodenal biopsy

The gold standard confirmation is still an upper endoscopy with biopsy of the small intestine, showing villous atrophy under the microscope. Pathologists grade the damage using the Marsh classification (Marsh 3 confirms celiac).

A no-biopsy diagnostic pathway is now accepted in children and being validated in adults. Very high tTG-IgA levels (greater than 10 times the upper limit of normal) combined with positive EMA predict villous atrophy in 97.5% of cases, which means many adults may soon be able to skip the endoscopy.

What Happens If You Do Not Treat It

Untreated celiac disease is not benign. A cohort study comparing patients with delayed diagnosis to those diagnosed promptly found roughly double the rates of major complications:

• Osteoporosis or low bone density: 40% vs 20%
• Infertility: 20% vs 10%
• Lymphoma: 5% vs 1%

The most serious cancer risk is enteropathy-associated T-cell lymphoma (EATL), a rare but aggressive intestinal lymphoma. Small bowel adenocarcinoma is also more common. Both are uncommon in absolute terms but the relative risk elevation is enough that most gastroenterologists consider early diagnosis and strict diet adherence a genuine cancer-prevention measure.

Nutritional deficiencies compound over time. Iron, calcium, vitamin D, B12, folate, and fat-soluble vitamins all take hits. Some patients develop refractory celiac disease, where the intestinal damage does not heal even on a strict gluten-free diet - a small subset of these progress to ulcerative jejunitis and lymphoma.

The Only Treatment: Strict Gluten-Free for Life

There is no medication, no probiotic, no enzyme, and no immunotherapy currently approved to treat celiac disease. The treatment is complete removal of gluten from the diet, indefinitely. Several drugs are in late-stage trials (larazotide acetate, latiglutenase, TAK-101, KAN-101) but nothing is approved yet.

"Strict" is the operative word. The FDA threshold for a food to be labeled gluten-free is less than 20 parts per million. Cross-contamination in home kitchens, restaurants, and shared fryers is enough to trigger both antibody production and intestinal damage - even without noticeable symptoms. About 30% of "gluten-free" restaurant meals in one study contained detectable gluten.

Healing takes time. Antibody levels typically normalize within 6 to 12 months of strict adherence. Intestinal villi can take 1 to 2 years to fully regenerate in adults, and some never do. Repeat tTG-IgA testing at 6 and 12 months after diagnosis is standard.

Tracking symptoms alongside meals is one of the more reliable ways to catch accidental gluten exposure, especially in the first year when the diet is still new and reactions can be delayed by days. Food-symptom correlation is also how many people first noticed the pattern in the first place - the same approach we outlined for identifying IBS food triggers applies here.

When to Get Tested

The American College of Gastroenterology recommends testing anyone with:

• Chronic diarrhea, constipation, bloating, or abdominal pain lasting more than a few weeks without clear cause
• Iron-deficiency anemia, particularly if it does not respond to oral iron
• Unexplained weight loss or failure to thrive
• An itchy, blistering rash (dermatitis herpetiformis)
• Unexplained elevation of liver enzymes
• Early or unexplained osteoporosis
• Recurrent miscarriage or unexplained infertility
• A first-degree relative (parent, sibling, child) with confirmed celiac disease - the risk is roughly 1 in 10
• Type 1 diabetes, autoimmune thyroid disease, Down syndrome, Turner syndrome, or Williams syndrome

Get the blood test before starting a gluten-free diet. This is the single most common mistake. Cutting gluten first and then getting tested a month later produces false negatives, and the only way to re-test accurately is a gluten challenge - eating the equivalent of two to four slices of wheat bread daily for at least six weeks, which is miserable for anyone who actually has celiac.

The Bottom Line

Celiac disease is common, systemic, and drastically underdiagnosed. If you have chronic digestive complaints, unexplained anemia, an itchy rash, early bone loss, or a first-degree relative with celiac, get the tTG-IgA test before you touch the gluten-free aisle. If you already went gluten-free and feel better, that is not proof of anything specific - it could be celiac, non-celiac gluten sensitivity, a FODMAP response, or a placebo, and only one of those has cancer risk attached.

Consistent tracking of stool form, meals, and symptoms is the single most useful thing an adult with unexplained digestive complaints can do before their next doctor visit. Two weeks of data reveals patterns that a symptom recall in a 10-minute appointment cannot.