How molecules cross the gut wall. Label amounts aren't absorbed amounts — absorption depends on form, the meal and your body's needs.
How it works, step by step
Digestion breaks food into small molecules.
Villi and microvilli create a huge absorbing surface.
Transporters move sugars, amino acids and minerals into gut cells.
Water-soluble nutrients go to the liver via the portal vein; fats enter lymph first.
Examples
Vitamin C boosts non-heme iron absorption; calcium can reduce it. Fat helps absorb vitamins A, D, E and K. Vitamin B12 needs intrinsic factor from the stomach.
Evidence & sources
Absorption of vitamin B12 from food requires intrinsic factor, a protein made in the stomach. Evidence: established. Known: Foundational physiology. Unknown: — Source: NIH Office of Dietary Supplements, Vitamin B12 — Health Professional Fact Sheet (Current revision).