Key Points:

Kiwi children have stopped getting fatter, but far too many are still fat.

Girls aged 5 to 14 who were overweight or obese dropped from 34 per cent in the first national survey in 2002 to 30 per cent in 2006-07, although this was partly due to changed definitions in the 2007 data released last year.

These were changed to body mass indexes of 25 and above for "overweight" and 30 for "obese", in line with international practice. Previously, slightly higher cutoffs were used for Maori and Pacific people because of their different body structures. The number of overweight or obese boys has stabilised, at 29 per cent in both surveys.

Longer-term figures for New Zealand are not available, but a controversial recent study in Australia found childhood obesity rose up to 1998 but has stabilised at 23 to 24 per cent overweight, including 5 to 6 per cent "obese".

"These findings directly contradict assertions in the published literature and the popular press that the prevalence of paediatric overweight and obesity in Australia is increasing exponentially," says the study's author Professor Timothy Olds. He says anti-obesity programmes such as walk-to-school schemes may be having an effect, or we may have reached a saturation point where all the children genetically predisposed to being fat are now fat.

Dr Robyn Toomath, of the New Zealand lobby group Fight the Obesity Epidemic, says obesity has stabilised all over the world. "You have the genetic predisposition and the environment reaching a steady state."

But there's no doubt that we still have a problem.

Olds' study, based on 27 local and national studies, found the proportion of Australian children who were overweight or obese roughly doubled between 1985 and 1998, from 12 per cent to 24 per cent.

In New Zealand, national figures for men show an increase from 51 per cent overweight or obese in 1977 to 62 per cent in 2002-03, and a further climb to 65 per cent in 2006-07, although this was partly because of the new definitions.

For women, the increase was from 37 per cent in 1977 to 50 per cent in 2002-03 and 55 per cent in the latest survey. Obesity alone more than doubled from 9 per cent to 23 per cent and 25 per cent in the last two surveys for men, and from 11 per cent to 25 and 26 per cent for women.

The recent slowdown in the rate of increase may be partly due to better economic times, as well as public health campaigns and a "saturation" effect, because poverty is associated with chronic stress which affects cortisol levels, making people fatter. Experts believe this is partly why obesity is more common in poor areas.

Conversely, Toomath warns, obesity may worsen again with the stress of the current economic meltdown.

"One can only predict that the obesity crisis will get worse as well."