We are very excited to have taken this step towards a future therapy

Dr Alison Wren, Imperial College London

The search for an effective appetite-limiting pill is also widespread, and only partly successful.

However, doctors from Imperial College, London, and the city's Hammersmith Hospital, claim that Ghrelin is the first circulating hormone which appears to increase food consumption in humans.

In their experiments, volunteers were given either a dose of Ghrelin or a saline placebo.

Huge losses

Their food intake was monitored closely over a set period.

Those who received the hormone consumed an average of 28% more calories than those who received the placebo.

This change in calorie intake, if sustained over a long period, could mean an enormous change in body weight.

A 75kg man, for example, increasing his calorie intake by just 1% over 10 years, would gain 15kg of weight.

Dr Alison Wren, from Imperial College, said: "There is currently little effective medical treatment for obesity and we are very excited to have taken this step towards a future therapy.

"We hope that by targeting Ghrelin with specific drugs, it may be possible to therapeutically control hunger."

Professor Steve Bloom, from Hammersmith Hospital, said: "The advantages of this kind of therapy may extend beyond the treatment of obese patients and include conditions that induce a dangerous loss of appetite, such as cancer.

"In cases such as this, Ghrelin supplements could potentially help to normalise eating patterns."