Intestinal Villi

The intestinal villi are so small you’d need a microscope to see individual ones — but they’re the central characters in the story of coeliac disease. Understanding what they are and what happens to them explains why coeliac disease causes the wide range of symptoms it does, and why the diet has to be strict.

What Are Intestinal Villi?

The small intestine is where almost all nutrient absorption happens. Its inner lining isn’t smooth — it’s covered in millions of tiny finger-like projections called villi, each one roughly 0.5–1.5mm tall. Each villus is in turn covered in even smaller projections called microvilli. Together, this structure creates an enormous surface area — estimated at around 250 square metres in a healthy gut. That’s roughly the size of a tennis court, folded into a tube about six metres long.

The villi are lined with specialised cells called enterocytes that absorb nutrients — iron, calcium, magnesium, B vitamins, fat-soluble vitamins (A, D, E, K), and more — and pass them into the bloodstream. Without healthy villi, this process breaks down.

In coeliac disease, the immune system’s response to gluten triggers chronic inflammation in the intestinal lining. Over time, this destroys the villi. The process is called villous atrophy. When villi flatten and disappear, the absorptive surface shrinks dramatically. The gut is structurally intact but functionally impaired.

The degree of damage is graded using the Marsh classification:

• Marsh 1–2: Inflammation increasing, villi still present
• Marsh 3a: Mild villous atrophy
• Marsh 3b: Marked villous atrophy
• Marsh 3c: Total villous atrophy — the villi are essentially gone

The clinical result of villous atrophy is malabsorption. Depending on severity and location within the small intestine, this can cause anaemia (iron or B12 deficiency), bone loss (calcium and vitamin D deficiency), neurological symptoms (B12 deficiency), fatigue, weight loss, and — in children — growth failure.

On a strict gluten-free diet, villi regenerate. This healing is real and measurable on a follow-up biopsy, though it takes time — often 1–2 years for adults.

What This Means for You

Villous atrophy is the physical basis of your diagnosis. It explains why symptoms can extend well beyond the gut, and why “I feel fine on gluten” doesn’t mean the intestine is undamaged. Healing requires removing gluten thoroughly and consistently — not approximately.

Related in the Coeliac Alphabet: Villous Atrophy · Enteropathy · Biopsy · back to the full A–Z.