A sugar you cannot digest, but bacteria can
Why Do Beans Make You Windy?
Beans carry a sugar your gut cannot break down, so it travels to the bacteria further along — and they produce gas.
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Step 1 of 5
Most food is absorbed before it gets far.
Starch, simple sugars and protein are taken apart and absorbed in the early part of the gut. Very little of a normal meal reaches the far end still edible.
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Step 2 of 5
Beans carry a sugar we have no enzyme for.
Their particular family of sugars needs an enzyme humans do not make. It goes through untouched, which means it arrives where the bacteria live still full of energy.
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Step 3 of 5
The bacteria are delighted.
Trillions of them live in the large intestine and are very good at breaking down exactly what we cannot. Fermenting that sugar is what they do, and gas is a by-product.
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Step 4 of 5
Soaking and rinsing takes some of it away.
The sugars dissolve in water. Soaking dried beans overnight and throwing away the water removes a good part of them before the beans reach the pot.
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Step 5 of 5
Eating beans often makes it milder.
The mix of bacteria shifts toward ones that handle those sugars tidily. People who eat beans regularly genuinely react less than people who eat them once a month.
Beans are one of the few foods that supply protein and fibre together, which is why almost every cuisine pairs them with a grain.
The short version
The sugar in beans needs an enzyme humans do not make, so it reaches the large intestine intact and the bacteria ferment it. Soaking and discarding the water removes much of it, and eating beans often shifts the bacteria toward tidier ones.
Try it yourself
Soak dried beans overnight. The water goes cloudy — that is the sugar leaving.