Geoff Watts examines new insights into why our gastrointestines misbehave in the way they do.
Packed away neatly inside your abdomen, your intestines don't take up much floor space.
But rolled out, their surface area would cover two tennis courts.A 'gut feeling' is becoming recognised as more than a poetic turn of phrase: researchers have discovered that the gut with its millions of nerve cells acts as the body's second brain with a vast range of activities.Could this hold the key to targeting treatment for some of the gut's mysterious diseases such as irritable bowel syndrome?
Tonight we find out how the body defends this huge area from attack by marauding bacteria.
If our gut immune system malfunctions, it can have devastating effects on the whole body.
Inflammatory bowel disease or IBD (a more severe condition than the infamous IBS) affects 1 in 400 people.
Patients and researchers alike are desperate to find a cure.
Geoff Watts explores the incredible ecosystem we harbour inside our intestines.
In the name of science, he has his stool sample analysed to find out how many bacteria live inside his guts.
"It's a veritable zoo," says Prof Peter Boriello of the Health Protection Agency, "in fact there are more bacteria inside your gut than people who have ever walked the planet".
Some are good, some are bad and most are downright ugly.
Trendy new probiotic supplements promise to boost our beneficial bacteria, but can a culture a day really keep the doctor away?