Taken apart, then absorbed
What Happens to Food You Eat?
Digestion breaks food into pieces small enough to cross into your blood.
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Step 1 of 5
Food must be broken to molecules.
Your cells can only use small molecules. Everything you eat has to be dismantled to that size before any of it is usable.
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Step 2 of 5
Chewing does the mechanical part.
Teeth multiply surface area, giving enzymes far more to work on. Saliva also starts breaking down starch while the food is still in your mouth.
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Step 3 of 5
The stomach is acid plus churning.
Strong acid unravels proteins and kills most microbes, while muscular walls churn everything into a thick soup.
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Step 4 of 5
Most absorption happens in the intestine.
The small intestine is where nutrients cross into the blood. Seven metres long, its lining is folded and fringed until the absorbing surface reaches something like thirty square metres.
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Step 5 of 5
The large intestine reclaims water.
What is left passes on, water is absorbed back, and gut bacteria feed on the remainder — producing some vitamins you actually use.
The whole journey takes a day or two, and only about seven metres of it is intestine.
The short version
Nothing is absorbed until it is molecule-sized. The stomach's acid unravels proteins and kills microbes, but the absorbing happens in seven metres of small intestine folded to something like thirty square metres. The large intestine takes the water back.
Try it yourself
Chew a piece of plain bread for a full minute. It turns sweet as saliva breaks starch into sugar.