The most recent figures show that in 2003 there were 24.2 million obese or overweight people in the UK.

The projected rise means that weight-related cancers are likely to rise from 10,500 cases per year to 12,000 in just seven years.

After smoking obesity is one of the most important preventable causes of cancer.

Lack of awareness

But few people are aware that being overweight or obese increases the risk of developing the disease.

A Cancer Research UK survey found that only 29% of overweight or obese people were aware of the cancer connection.

Professor Tim Key, an expert on diet and cancer, said: "It is now well established that being overweight increases the risk of developing several types of cancer.

"The effects on breast and womb cancer are almost certainly due to the increased production of the hormone oestrogen in the fatty tissue.

"We are less sure of the precise mechanisms in other obesity related cancers but we can confidently predict that the number of these cases will increase unless the rise in obesity in Britain can be reversed."

Research in the US has found that among men and women who have never smoked the risk of overall cancer death is increased by up to a third in obese people.

Cancer Research UK is calling for a comprehensive strategy to halt the rise in obesity in the UK, which must be particularly targeted at children and young adults.

Women who are overweight or obese are at increased risk of womb cancer and postmenopausal women have a greater risk of developing breast cancer.

There is also evidence for a link between obesity and cancers of the bowel and kidney.

Poor survival

Obese people who develop cancer are also less likely to survive than those with a healthy weight, possibly because the cancer is more difficult to diagnose and is therefore not treated until it is more advanced.

Dr Lesley Walker, the charity's director of cancer information, said: "Eating healthily and exercising regularly is the best way to maintain a healthy body weight and to reduce your cancer risk."

During the trial, 'healthy' volunteers were given two anti-depressant drugs, which raised the levels of both chemicals in their brain.

Increased serotonin levels appeared to improve sensitivity to sweet and bitter tastes, while increased noradrenaline levels appeared to improve sensitivity to bitter and sour tastes.

Exciting breakthrough

Lead researcher Dr Lucy Donaldson said: "Because we have found that different tastes change in response to changes in the two different neurotransmitters, we hope that using a taste test in depressed people will tell us which neurotransmitter is affected in their illness."

Dr Jan Melichar, the lead psychiatrist in the study, said: "This is very exciting. Until now we have had no easy way of deciding which is the best medication for depression.

"As a result, we get it right about 60-80% of the time. It then takes up to four weeks to see if the drug is working, or if we need to change it.

"However, with a taste test, we may be able to get it right first time."

The findings also suggest somebody who is anxious or stressed will have a less sensitive sense of taste - which may explain why people with depression have a diminished appetite.

Professor Dave Kendall, an expert on depression at the University of Nottingham, said the research was interesting - but was unlikely to be able to determine which drugs a patient should take.