Our own stomachs may be something of a dark mystery to most of us, but new research is revealing the surprising ways in which our guts exert control over our mood and appetite.
Not many of us get the chance to watch our own stomach's digestion in action.
But along with an audience at London's Science Museum, I recently watched live pictures from my own stomach as the porridge I had eaten for breakfast was churned, broken up, exposed to acid and then pushed out into my small intestine as a creamy mush called chyme.
I had swallowed a miniature camera in the form of a pill that would spend the day travelling through my digestive system, projecting images onto a giant screen.
Its first stop was my stomach, whose complex work is under the control of what's sometimes called "the little brain", a network of neurons that line your stomach and your gut.
Surprisingly, there are over 100 million of these cells in your gut, as many as there are in the head of a cat.
The little brain does not do a lot of complex thinking but it does get on with the essential daily grind involved in digesting food - lots of mixing, contracting and absorbing, to help break down our food and begin extracting the nutrients and vitamins we need.
And all those neurons lining our digestive system allow it to keep in close contact with the brain in your skull, via the vagus nerves, which often influence our emotional state.
For instance when we experience "butterflies in the stomach", this really is the brain in the stomach talking to the brain in your head. As we get nervous or fearful, blood gets diverted from our gut to our muscles and this is the stomach's way of protesting.
Hunger hormones
To accommodate a big meal your stomach has to expand from the size of a fist to around 2 litres. That's a 40-fold increase.
We used to think that stretch receptors in the stomach told the brain when the stomach was full, time to stop eating. But it turns out that the hunger signals produced by your stomach are far more sophisticated than that.
Understanding that has helped doctors treat father of 4, Bob Lakhanpal, who had hardly ever felt full, no matter how much he ate. As a result he had grown to 20 stone.
