Kiwi obesity - 'even the skinny people are fatter'

New Zealand is overweight - collectively the adult population weighs more than 232,000 tonnes.

But while New Zealand accounts for only 0.08 per cent of the total weight of the world adult population, it makes up 0.22 per cent of the world's excess weight due to obesity, according to a new study.

Using 2005 data from the United Nations and World Health Organisation, researchers from the London School of Hygiene and Tropical Medicine estimate that the adult human population weighs a total 287 million tonnes. Fifteen million tonnes of this are classed as overweight - of which 3.5 million are obese.

Of New Zealand's total weight, 28,500 tonnes are overweight and of that, 7700 tonnes are obese weight.

One of the study's authors, Professor Ian Roberts, said the world was getting fatter and the study was a way to put numbers on what everyone could see.

"The whole world is getting fat ... everybody's fat, I'm fat, the Queen's fat - everybody," he told the Herald.

"Even the skinny people are fatter than they would have been 20 years ago."

But while New Zealand is weighing in heavy, the United States is even worse. It has about 5 per cent of the world's adult population but accounts for about a third of the excess weight because of obesity.

If every other country was as overweight as the United States, the world's total biomass would increase by 58 million tonnes, which is equal to about one billion more people, according to Professor Roberts.

But if the population of every country had the same biomass as Japan - one of the leanest countries - the world's total biomass would fall by 14.6 million tonnes.

Professor Roberts said how fat a country was correlated to how much fossil fuel it burned.

"Fossil fuel is making the whole world fat because food is made out of fossil fuel ... and at the same time we move our bodies less than through the whole course of human history, burning fossil fuels instead to get around, and that's not what we were designed to do."

New Zealanders liked to think they had a "clean, green image and that everyone cycles everywhere" but the study's findings showed otherwise, Professor Roberts said. "It's closer to the US than most New Zealanders would like to think."

The researchers used country-specific data on body mass index and heights to estimate the biomass of the world's adult population and calculated the total biomass as the product of population size and average body mass.

Obesity in New Zealand

* One in four adults (aged 15 years and over) is obese.
* 44.7 per cent of Maori adults are obese.
* One in every 12 children (aged 2 to 14 years) is obese.
* One in every five children is overweight.

- Figures from the Ministry of Health