Digestive health
How digestion works
A simplified tour of the journey food takes, and where the everyday things people ask about — hydration, fibre, movement and routine — actually come into play.
The journey
From a mouthful to the end of the line
The whole journey typically takes somewhere between one and three days, and varies considerably between people. The timings below are broad general ranges rather than targets to measure yourself against.
Seconds to a minute
Mouth
Digestion starts before anything is swallowed. Chewing breaks food into smaller pieces and saliva begins breaking down starches. Eating quickly skips much of this, which is one reason it is often linked to bloating.
Around 2 to 4 hours
Stomach
The stomach mixes food with acid and enzymes into a semi-liquid form. It releases this into the small intestine gradually rather than all at once.
Around 3 to 5 hours
Small intestine
Most nutrient absorption happens here, across a surface far larger than its length suggests. What is left moves on to the large intestine.
Around 10 to 20 hours
Large intestine
Water and some minerals are absorbed here, and the remaining material is gradually formed into stool. The longer it stays, the more water is drawn back — which is why transit time and hydration are so closely linked.
Continuous
Colon
The colon is the main section of the large intestine. It is home to a large community of bacteria that ferment some of the fibre we cannot digest ourselves.
Until you go
Rectum
Stool is stored here until the urge to go is felt. Regularly ignoring that urge can, over time, make a routine harder to keep.
Stage by stage
Each stage, briefly
Mouth
Digestion starts before anything is swallowed. Chewing breaks food into smaller pieces and saliva begins breaking down starches. Eating quickly skips much of this, which is one reason it is often linked to bloating.
Stomach
The stomach mixes food with acid and enzymes into a semi-liquid form. It releases this into the small intestine gradually rather than all at once.
Small intestine
Most nutrient absorption happens here, across a surface far larger than its length suggests. What is left moves on to the large intestine.
Large intestine
Water and some minerals are absorbed here, and the remaining material is gradually formed into stool. The longer it stays, the more water is drawn back — which is why transit time and hydration are so closely linked.
Colon
The colon is the main section of the large intestine. It is home to a large community of bacteria that ferment some of the fibre we cannot digest ourselves.
Rectum
Stool is stored here until the urge to go is felt. Regularly ignoring that urge can, over time, make a routine harder to keep.
What influences it
Hydration, movement, fibre and routine
These four come up repeatedly because each affects a different part of the journey. Together they shape a routine far more than any single change does.
Hydration
Water is absorbed in the large intestine. Less fluid available means firmer stool.
Movement
Regular activity supports the muscular movement that carries material along.
Fibre
Adds bulk and holds water. Increase it gradually, and increase fluids alongside.
Routine
Digestion follows daily rhythms. Consistent meal and sleep times help them settle.
Curious what commonly disrupts this?
Our symptoms and causes hub covers diet, hydration, stress, travel, medication, aging and more.
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