The industrialisation of our eating habits is rivalled only by that of our slimming practices, reports Julia Stuart

The romans built vomitoriums to control their food-intake. Today, we prefer to spend money, and lots of it. Last month, a report revealed that Britons now fork out almost £70m a year on slimming aids, such as pills and meal replacement drinks. Add that to the books, magazines, reduced fat meals, diet drinks, videos and clinics and you've got an industry raking in billions of pounds a year.

More than a quarter of all Britons are on a diet, and there is no sign of the national obsession waning. Formerly a female preserve, men and children are now taking up the habit. Almost one in 20 men buy over-the-counter slimming pills each month. Five and six-year-old girls know what the word "diet" means, and by eight some are on one.

So why are we so preoccupied with losing weight? Dr Andrew Hill, chairman of the Association for the Study of Obesity, and a senior lecturer in behavioural sciences at Leeds University, blames, in part, the fashion industry for changing "the acceptability of women's body shape through the last century ... [Now] there's an enormous mismatch between visual images and the reality of life. And we are sucked into this very superficial visual aspect of life."

Health worries have also fuelled the obsession. Concern over weight and its affect on health started at the beginning of the last century when life insurance companies made an association between body weight and life expectancy.

But far from the nation's collective midriff diminishing, we are now fatter than ever, and are, to our shame, the most overweight Europeans. According to the National Audit Office, nearly two thirds of men, more than half of women and one in 10 children under 11 are overweight.

Dr Hill blames our weight gain on changes in society, such as the decline in more "physical" jobs and the introduction of central heating. "It's probably because our bodies haven't adapted to environmental change, which has encouraged us to eat more than we did 30 years ago, but prevents us from expending the same amount of energy."

Susie Orbach, author of Fat is a Feminist Issue, lays the blame for our collective saddlebags and love handles on dieting, however. "If you are obese you probably got there by dieting," she says. "Diets create eating problems.

"The minute you have a diet that excludes certain foods, or is related to calories, carbohydrate values or food-combining, you are interrupting a process which ought to be completely natural."

Orbach claims that much of the dieting industry is "propagating false advertising, and a lot of them should be prosecuted." So why does she believe people continue to diet, despite the fact it has been known for years that dieting doesn't work? (96 per cent of dieters regain all weight lost within two years) "Because they feel desperate and they don't really know how to eat," she says.

Michael Rennie, professor of physiology at the University of Dundee, would also like to see the back of the diet industry. "Diets are a total waste of money," he says. "Your body size depends on the balance between what you eat and what you expend in terms of energy. This information is not new, it's been known for over 100 years. If you eat more than you need it sticks, if you eat less then you'll easily lose weight. It's as simple as that. The diet industry is basically providing a service which nobody who has grasped these simple truths actually needs."

Dr Hill, too, has reservations. "Generally speaking diets do not appear to work, although a lot of people, for some time, find they can lose weight. What people tend not to do is separate losing weight from maintaining weight loss." He believes that those who do succeed in keeping lost weight off tend to be less obsessed. "They cope with transgressions better, and don't make a song and dance about what they are doing."

Catherine Collins, spokes- woman for the British Dietetic Association, believes that successful weight loss is all down to will-power and attitude. "People go to a slimming club where they get a lot of support and encouragement. Then they stop going and their portions gradually increase, every day they have a little treat, and the weight creeps back on. It's a matter of maintaining that level of will-power over a long period of time, which is difficult."

While Dr Hill recognises the drawback of dieting, he believes it has its place in society for those who really need it – not people who simply wish to look like celebrities. "Dieting is a necessary thing: we have a major explosion in obesity. But we certainly need to stop the unlicensed diet industry from operating – those people who offer false promises and fleece their customers. And we need to take the pressure off image".

But how to do it? For disenchanted dieters who wish to throw away the scales, pills, potions and milkshakes, and welcome real food back into their lives, Orbach has this advice: eat when you're hungry, be extremely conscious while eating so you can actually taste the food and realise when you're full, then stop.