The Australian head of fast-food chain McDonald's says there's no mystery surrounding childhood obesity: kids are fat because they don't exercise as much as they used to.
Chief executive Peter Bush also says McDonald's, according to the chain's own research, provides just one in every 72 meals an average child eats.
"You've got to look at those other 71 meals kids consume that often come out of the cupboard at home," Mr Bush told a federal parliamentary inquiry into obesity, sitting in Sydney today.
"Where we sit on this is that we probably look at it as a very perplexing and complicated issue.
"Certainly the studies have indicated that the issue is linked to a change on lifestyle - kids exercising less, watching more TV, kids playing video games."
Mr Bush said academics where now properly studying the causes of obesity, but most pre-existing data blaming fast food was inconclusive.
"When the very first obesity summit was held in Sydney in October 2002, my predecessor sat through the two days of that session," he said.
"Through that time, overwhelming evidence was presented, but not substantiated, that fast food was the culprit.
"What also emerged at that time was there were very few studies completed worldwide at that stage."
Mr Bush said fear of crime was a factor in obesity, arguing parents do not allow children to walk to school anymore.
The House of Representatives standing committee inquiry, which began in May, is looking at the increasing prevalence of obesity and future implications for the health system.
University of Sydney Associate Professor Jenny O'Dea presented the findings of a study on obese children and a survey of 345,713 adults.
It showed poorly-educated parents were more than twice as likely to have obese children as well-educated mums and dads.
The Roy Morgan survey also showed the rate of obesity for adults in the lowest socio-economic groups grew at almost triple the rate of those belonging to the highest earning and educated groups between April 2000 and March 2007.
Nearly a third of people in the lowest socio-economic group were regarded as obese in March last year, compared with 26.6 per cent in April 2000. In the highest socio-economic group, 17.8 per cent were obese, up from 15.9 in 2000.
Dr O'Dea said governments should rethink obesity campaigns, saying they must address social inequities rather than opting for "shame and blame" strategies, which did not work.
She also said the international standard for measuring obesity was generally fair, but the label should be treated with care as the body mass of some ethnic groups differed.
"You can't assume that an overweight, obese child is carrying too much fat," she said.
"There are kids who fit into that category. They are the the Samoan kids and the Fijian kids and the Greek boys who are very muscular and the Lebanese boys."
Dr O'Dea studied 960 families of children, from years two to six, in 10 primary schools across regional and rural NSW.
She discovered 2.7 per cent of tertiary-educated mothers had obese children compared with six per cent of mums who had completed year 10 or less.
Seven per cent of fathers in the low-educated group had obese children, while the figure was three per cent for those in the highly-educated group.
