The second brain in our stomachs

Six years ago, at the age of 28, he had a heart attack. To help him lose weight, he was recently given gastric bypass operation.

Now, you might think that just reducing the size of the stomach would be enough to sort out Bob's problems, because the smaller the stomach the less you eat.

But that does not seem to be what happens according to his surgeon, Mr Ahmed Ahmed, at London's Charing Cross Hospital.

"The modern thinking is that by doing the surgery you're producing changes in various hormones, chemical messengers which affect hunger levels and fullness levels, which in turn cause the weight loss.

"Bob's gastric bypass surgery separated off and isolated the part of his stomach which produces most ghrelin, a hormone which appears to play a key role in making you feel hungry." The hope was that this would result in a permanent fall in production of ghrelin.

His new shrunken stomach was then attached further down his small intestine, to a section known as the ileum which secretes a different gut hormone, PYY, which is responsible for making you feel full.

When we eat, it normally takes 20 minutes for food to get from the stomach to the ileum, causing the release of PYY and the message to the brain, "I'm full".

That is why it is better to eat slowly, to give the stomach a chance to tell the brain you have had enough before you overeat.

With his ileum so much nearer his stomach, Bob's brain now gets that message much quicker.

Six weeks after his operation, he had already lost three stone.

"These days I only have to eat a small amount of food and I feel full - I'm happy with that and I can stick with that. Family's happy, I'm happy, can't wait to lose more weight."

Gastric bypass is only available for more extreme cases but there is now intense interest in developing drugs that mimic the actions of PYY.