However, given the extent of obesity, the assumption of passivity now seems to be the only workable alternative.

As long as very fat people existed in numbers small enough to be marginalised, a 'non-victim' attitude towards them was possible. We lumped them together with other abnormal or irresponsible people and felt they deserved our disdain because they chose to indulge in self-destructive behaviour.

But obesity is now far too prevalent for that. The number of adults who have slipped into an unhealthy imbalance between moving and eating has already reached sociological critical mass. Further proof it has shifted from the individual to the social, and from the abnormal to the normal, took place when children started growing up that way.

This banalisation of obesity is having a deep effect on what can be done about it.

The first step in most programmes is nutritional education and tips on how to change thinking and behaviour around eating. A common bad habit is parents rewarding themselves and their children for healthy eating with unhealthy food. (Eating a salad means a reward of ice cream.) Others are family-endorsed binges, where food is treated as entertainment, as comfort and as a popular social activity.

One approach to treatment is to ask the obese person's family to help protect against outside pressures working against efforts to lose weight. This whole-family approach may result in fewer heavy children becoming very fat adults. However, adults are less treatable, and for everyone it is an uphill struggle.

Highly obese people never get better alone. They improve somewhat, but only when psychological help is accompanied by drugs or surgery. The less obese do not do so well either - hence the success of the dieting industry. Most general practitioners give useless, even harmful advice 'masquerading as behaviour therapy' according to University College London research dietician Helen Crocker. They do not recognise, for example, that after a certain point, lifestyle modification alone is hopeless.

It is tricky to try to reduce body fatness in children while still providing enough energy for proper growth. Heightening children's awareness about their health, weight and especially eating can be dangerous. Yet, children know very well society values thinness; the 'he'll grow out of it' option is risky, too.

Overall, while psychologists have been active in research, psychological interventions alone have a low success rate. People who go through programmes often lose only about 10 per cent of their weight, then regain it within five years.

Aggressively 're-stigmatising' fat is not the solution. But we can learn from anti-smoking campaigns. It requires gentle but insistent long-term political will in education and co-ordinated action across society to make a difference.

Jean Nicol is a psychologist specialising in issues of cultural identity and change in an era of globalisation