The developed world is suffering an obesity epidemic, with large numbers of children seriously overweight, according to researchers.

The number of obese children has almost doubled in the past two decades, a study shows, and the findings also point to increased adult obesity.

Children in large cities with poorly educated parents are at the greatest risk according to the researchers at Leiden University Medical Center in the Netherlands.

They collected weight and height details for 14,500 children between 1996 and 1997 and found that 13% were overweight, mirroring similar studies in the UK and the US.

They defined being overweight as having a body mass index of more than 25kg per square metre of body size.

They also found that the age at which weight flattens out during childhood, known as adiposity, had fallen from six-years-old in 1980 to five-and-a-half in 1997. The earlier this occurs, the greater the chance of obesity in adulthood, they said.

The research team led by Dr Miranda Fredriks blamed the rise in obesity on not eating breakfast, snacking and eating too many foods containing invisible fats.

Public education

They called for a public education programme to tackle child obesity.

Writing in Archives of Disease in Childhood, they said: "During the past two decades, a striking in crease in the prevalence of obesity has occurred in Western countries.

"Because adverse health effects later in life might be consequent upon childhood obesity, we recommend that obesity prevention early in life should be a priority in child public health care."

Dr John Reilly, head of Glasgow University's Childhood Obesity Group, said the Dutch findings mirrored the results of studies he has carried out in the UK.

He has found that the amount of obesity in children has risen from 5% in the late 1980s to as much as 17% in the 15-year-old age group in the late 1990s.

He said: "We are storing up problems for the future. I have no doubt that we should be concerned about the long-term implications."

He questioned, though, the cause of the rise in obesity, saying that there was no evidence in Britain of increased calorie intake among children and blaming reduced levels of physical activity.