FAD DIETS: WHY THEY MAKE YOU FAT

He warns that if current eating trends continue we will have a ­dramatically shortened life expectancy, obesity will be the main cause of death and there will be a surge in obesity-caused liver disease.

Fad plans, such as high-protein or high-carbohydrate diets, can actually be unhealthy, and rarely work as a long-term way of managing weight, he believes.

Similarly, slimming aids that ­suppress the appetite or speed up metabolism may produce short-term results but the weight soon creeps back on.

Despite this, almost £30billion is spent globally on the diet and ­slimming industry each year.

Catherine Collins, a clinical dietician working in the NHS, backed Prof Hawkey’s argument.

“The problem with these sort of ­diets is it’s extreme dieting which most people can’t ­continue,” she said.

To lose weight and keep it off she advises simple techniques such as keeping a food diary, including fruit and vegetables at every meal and down-sizing treats such as chocolate to smaller portions.

“If you want to lose weight, it’s a marathon, not a sprint,” she said. In his speech, Prof Hawkey will say: “What’s important is to recognise that despite the popularity of fad ­diets, we are losing a grip on the fight with obesity.

“Our research shows that 62 per cent of the public think obesity will continue to increase for at least the next 10 years.”

Prof Hawkey will present the alarming new research at Gastro 2009, the world’s largest gastroenterology conference in London featuring 12,000 scientists.

The YouGov study, commissioned by the British Society of Gastroenterology, aims to establish the public’s attitude towards food and dieting.

It found that nearly half of Britons (49 per cent) classify themselves as overweight. It also discovered one in 20 women would try the Atkins diet if trying to lose weight.

Speaking to the Daily Express ­before the conference, Prof Hawkey said: “Despite an interest in lots of different types of diet, as a society we are getting fatter.

“The problem is we have a lot of ­diets around and we have people starving themselves, then putting the weight back on and that is not the way to go.

“Choosing a diet for a particular content isn’t going to stop people getting overweight.

“The issue is obesity and we don’t know how to tackle it.

“In the whole of human history, there has never been anything quite like this.

“It is going to become the biggest cause of death and the biggest cause of liver disease, overtaking alcohol.”