THEY ARE often endorsed by celebrities and are a staple of women's magazines, but now fad diets are being blamed by experts for confusing people about healthy eating.

A new survey carried out by watchdog body the Food Standards Agency (FSA) has revealed that despite efforts to encourage people to ditch unhealthy habits, most consumers are still unclear about what makes up a balanced diet.

Just over one in 10 people correctly said it was important to eat lots of starchy foods, and only 45% of those surveyed knew that tinned fruit and vegetables counted towards their "five a day" target.

More than half, 58%, realised that foods high in fat and sugar should be eaten only occasionally, but nearly one in five wrongly thought that eating plenty of fruit and vegetables would outweigh the consumption of sugary, fatty foods.

However, the survey of more than 2000 people found that one message appears to be getting through, with nearly three-quarters recognising the importance of lots of fresh fruit and vegetables.

The FSA has redesigned the image it uses to show what makes up a healthy diet for the first time since 1994, in order to make it clearer. The recommended intake of different food groups has not changed, but the newly designed "eatwell plate" uses photographs of different foods and renames some food groups.

FSA head of nutrition Rosemary Hignett said consumers ought to know the proportions of each food group needed for a healthy balanced diet.

"It's not a 10-minute fad. It's a diet for life that we know will help reduce the number of diet-related illnesses such as heart disease, stroke, diabetes and some cancers, which are on the rise in the UK," she said. "This is about a simple, straightforward approach that allows us to enjoy a varied diet that ncludes foods from all groups."

The Atkins diet, perhaps the most famous food craze, took the world by storm five years ago and had celebrity fans including Renee Zellweger. It advocated piles of fatty food and a ban on carbohydrates, and won over millions who dreamt of shrinking to a svelte size by gorging on fry-ups. But doctors branded the diet one of the most dangerous ever, arguing that its high fat content would lead to heart disease.

At the peak of the mania in 2003, some 110,000 Atkins diet books were sold in Britain in a week. However, a year later, after the diet's creator, New York GP Robert Atkins, died, reportedly from obesity-related medical complaints, the bubble burst and weekly sales plummeted to a tenth of that.

The Cambridge diet was one of the first fad-food plans to become a global phenomenon, gaining popularity in the 1980s. A spin-off from a regime developed for astronauts in the 1960s, the lucrative enterprise involved some dieters eating only food produced by the company. But medical experts issued health warnings over the extremely low-calorie diet, which asked people to slash their energy intake to a quarter of normal.

The Zone diet was another bizarre theory that sucked people in, with its founder Barry Sears adopting "hormonal thinking", an approach that claimed a person's hormone levels dictated what combinations of foods they should eat. Other famous fads are the cabbage soup diet, the grapefruit diet and the blood type diet, which prescribes foods according to your blood group.

The most recent craze has been the Glycemic Index (GI) diet, which recommends people eat more foods with low GI ratings, such as oats, that release energy over a long period. Pop star Kylie Minogue and former US president Bill Clinton are among those reported to have followed this regime.

Doctors are more welcoming of this approach, as it is not inherently restrictive, but warn followers to eat a balanced range of foods.