How digestion works: what happens to food after you eat it
Digestive enzymes: how your body cuts food into pieces it can take in
Teeth can only break food into bits. Something far smaller does the real cutting, and it starts before you swallow. Meet the digestive enzymes, and the long chains that your food is made of.
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1
Look very closely at one grain of rice from your bowl. Apart from water, most of it is starch. And starch is a long chain of small sugars, each one joined to the next by a bond. Each sugar is called glucose.
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Apart from water, the chicken is mostly protein, and protein is a chain too. It is made of small building blocks called amino acids.
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Your gut wall lets in single sugars, never a chain. So the starch must be cut apart, bond by bond.
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The cutters are enzymes. An enzyme is a molecule, a tiny thing that your body makes. An enzyme grabs a chain, cuts one bond and lets go. Then it grabs the next one, again and again, very fast.
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But each enzyme fits one kind of bond only. The one that cuts starch cannot cut protein, and the one that cuts protein cannot cut starch. So your body makes many kinds of enzymes.
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The first one is already in your mouth. Your saliva, the liquid in your mouth, holds an enzyme called amylase. While you chew, it starts cutting the starch of your rice. Other enzymes will finish the job further down.
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Some chains in your beans have bonds that none of your enzymes fit. This is fibre. No cut, no way in: it will travel the whole tube. We will meet it again at the very end.
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Then you swallow. The muscles of the pipe from your mouth to your stomach squeeze behind the food and push it down, one wave at a time. At the bottom waits a bag full of acid.
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Quick check
Milk and its sugar.
Show the answer
Most of it is not cut, so it cannot cross the gut wall. It goes on down the tube, like fibre.
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Go further
A word, and a fact, past the story.