In functional and integrative psychiatry, patterns start to announce themselves long before they show up in guidelines.

Over the past several months in my clinical practice, I have diagnosed celiac disease in multiple young adult men who presented not with diarrhea, abdominal pain, or weight loss, but with psychiatric and cognitive symptoms: chronic low mood, brain fog, fatigue, poor motivation, memory issues, and anxiety. Neither had prominent gastrointestinal complaints. Both had subtle but telling micronutrient deficiencies. Both had positive serologies highly suggestive of celiac disease.

This raises an important question: Is celiac disease becoming more prevalent, or are we simply getting better at recognizing it in patients who do not fit the classic gastrointestinal picture?

The answer is probably both. But in psychiatry, the under-recognition is particularly stark.

Silent celiac is not rare

Celiac disease is still widely imagined as a gastrointestinal disorder. In reality, nearly half of adults diagnosed with biopsy-proven celiac disease present without classic GI symptoms. Large epidemiologic studies suggest that approximately 48 to 49 percent of patients present primarily with extraintestinal complaints, including fatigue, anemia, osteoporosis, transaminitis, infertility, neuropathy, and neuropsychiatric symptoms.

In other words, the gut may be the origin of the problem, but it is not always the loudest organ in the room.

Patients without GI symptoms also experience significantly longer diagnostic delays. While patients with abdominal pain or diarrhea are often diagnosed within months, those with non-gastrointestinal presentations may go years before celiac disease is even considered. During that time, chronic inflammation and malabsorption quietly shape brain function, energy, mood, and cognitive performance.

Two cases that changed how I screen

Both of the following patients were young adult men referred for psychiatric care, not gastroenterology.

One patient in his early 30s presented with brain fog, chronic low mood, low motivation, and mild anxiety. Initial labs showed low iron, low-normal vitamin B12, and low vitamin D. Family history was notable for autoimmune disease, as his mother has Hashimoto’s thyroiditis. He denied significant gastrointestinal symptoms. A comprehensive celiac panel showed markedly elevated tissue transglutaminase IgA and positive endomysial antibodies, consistent with celiac disease.

Another patient in his mid-20s presented with fatigue, impaired concentration, low motivation, memory complaints, and anxiety. He also had micronutrient deficiencies and no prominent GI symptoms. Again, serologic testing strongly supported a diagnosis of celiac disease.

In both cases, the psychiatric symptoms were genuine and impairing. But they were not the whole story.

When the intestine cannot reliably absorb iron, B12, vitamin D, and other micronutrients, the brain pays the price. Neurotransmitter synthesis, mitochondrial energy production, inflammatory signaling, and circadian regulation all depend on adequate nutritional status. Chronic immune activation further compounds the problem.

From a functional psychiatry lens, these are not “psychosomatic” symptoms. They are neurobiological consequences of systemic disease.

Are we seeing more celiac, or testing more thoughtfully?

Celiac disease prevalence does appear to be increasing over time, likely due to a combination of genetic susceptibility and modern environmental factors. But in mental health settings, the larger driver is probably detection: We are finally testing for medical contributors to psychiatric symptoms instead of assuming the brain exists in isolation.

Historically, celiac screening has been triggered by diarrhea, bloating, or weight loss. When those cues are absent, the diagnosis is often missed. Functional psychiatry tends to notice constellations of findings that point toward malabsorption and immune dysregulation: low ferritin or iron saturation, low or borderline B12, low vitamin D, difficulty maintaining weight, fatigue, brain fog, mood symptoms that respond poorly to standard treatment, and family history of autoimmune disease.

The brain does not float above the body. As my mentor James Greenblatt, MD, often says, “We have a neck.” In other words, the brain is not separate from the body. What happens below the neck inevitably shapes what happens above it.

Diagnostic considerations in adults

Current adult guidelines still recommend confirmation of celiac disease with small bowel biopsy following positive serologic testing. While very high tissue transglutaminase IgA levels carry a strong positive predictive value, serology alone is not considered definitive in most adults, given the lifelong implications of the diagnosis.

Recent meta-analytic data suggest that serology-only approaches, while highly specific, have lower sensitivity, meaning some cases may be missed without biopsy confirmation. This matters because many adults with psychiatric or neurologic presentations already experience prolonged diagnostic delays. Premature reassurance can prolong years of untreated inflammation and nutrient malabsorption.

One practical clinical point is essential: Screening must occur before a patient adopts a gluten-free diet. Once gluten is removed, serologic markers may normalize, making diagnosis far more difficult.

Why this matters in psychiatry

Celiac disease is not a niche gastroenterology diagnosis. It is a systemic autoimmune condition with meaningful neuropsychiatric consequences.

In clinical practice, many patients labeled with treatment-resistant depression, ADHD, anxiety, or “brain fog” have never had their iron stores, B12, vitamin D, or malabsorption evaluated. Some of these patients will have celiac disease. Others will have related conditions such as autoimmune gastritis, SIBO, or inflammatory bowel disease. The shared lesson is that psychiatric symptoms often reflect underlying physiology.

Functional psychiatry does not replace psychopharmacology or psychotherapy. It contextualizes them. When inflammation is ongoing and nutrients are not being absorbed, psychiatric treatments are often forced to work against the current of biology.

The bigger takeaway

Celiac disease is not just a gastrointestinal disorder. In many adults, it is a neuropsychiatric condition wearing a medical disguise.

The clinical question is not whether every patient with depression needs a celiac panel. The real question is whether clinicians are willing to investigate systemic contributors when psychiatric symptoms do not fully add up. In functional psychiatry, that willingness changes outcomes.

The gut and the brain share an immune system, a metabolic budget, and a bidirectional signaling network. When one is chronically inflamed, the other rarely remains untouched.

Carrie Friedman is a dual board-certified psychiatric and family nurse practitioner and the founder of Brain Garden Psychiatry in California. She integrates evidence-based psychopharmacology with functional and integrative psychiatry, emphasizing root-cause approaches that connect neuro-nutrition and gut–brain science, metabolic psychiatry, immunology, endocrinology, and mind–body lifestyle medicine. Carrie’s clinical focus bridges conventional psychiatry with holistic strategies to support mental health through nutrition, physiology, and sustainable lifestyle interventions. Her professional writing explores topics such as functional medicine, autism, provider well-being, and medical ethics.