Digestive · Intestinum tenue
Small intestine
Seven metres of tubing folded into your abdomen, with the absorbing surface of a studio apartment.
- Length
- ~6 to 7 m
- Absorptive surface
- ~30 m²
- Transit time
- 3 to 5 hours
- Surface multiplier
- ~600x versus a smooth tube
What it does
Where you actually absorb your food. Nutrients cross into blood and lymph here across the duodenum, jejunum, and ileum, aided by bile from the liver and enzymes from the pancreas.
The marvel
Folds, then villi on the folds, then microvilli on the villi. That fractal stacking multiplies the surface area of a plain tube by roughly 600 times, giving about 30 square metres of absorptive surface inside a space the size of a shoebox.
How to serve it well
Fibre, from food, consistently
Most people eat well under the recommended 25 to 30 g a day. It is one of the few dietary changes with broad, durable evidence.
Do not self-diagnose coeliac disease
Testing requires you to still be eating gluten. Going gluten-free first makes the diagnosis much harder to confirm.
Treat antibiotics as a real intervention
They are essential when indicated and disruptive when not. The gut community takes time to recover.
Be skeptical of "leaky gut" products
Intestinal permeability is a genuine research area. The commercial supplement category built on it has run far ahead of the evidence.
Book an appointment
- Persistent bloating, cramping, or diarrhoea lasting weeks
- Unintentional weight loss
- Symptoms that reliably follow specific foods
- Iron or B12 deficiency found on blood tests
Emergency, go now
- Severe abdominal pain with vomiting and no bowel movement or gas
- A rigid, board-like abdomen
- Significant blood in stool
What you may have been told
“Undigested food and mucus build up along your intestinal walls for years.”
The "mucoid plaque" shown in cleanse marketing is the cleanse product itself, gelled in the gut. Endoscopy on people who have never cleansed shows nothing of the kind lining a healthy bowel.
Where this comes from
- National Institute of Diabetes and Digestive and Kidney Diseases · Digestive diseases
- Coeliac UK · Getting diagnosed
- NHS · Fibre and healthy eating
LUMEN is education, not medical advice, and it cannot know anything about you. It does not diagnose. If something here matches what you are experiencing, take it to a clinician who can examine you.