About 1.5 m long. Absorbs water and salts and hosts trillions of bacteria that ferment fiber.
Fermentation
Bacteria ferment fiber into short-chain fatty acids such as butyrate, a fuel for colon cells, plus gases.
Water
Most remaining water is reabsorbed here, forming stool.
Evidence & sources
The large intestine absorbs water and turns the remaining waste into stool; its bacteria help break down nutrients. Evidence: established. Known: Basic physiology. Unknown: How specific gut bacteria affect health is an active research area. Source: NIH NIDDK, Your Digestive System & How It Works (Current revision).