Research at La Trobe University in Melbourne has revealed that the number of fat adolescents has almost doubled since the last national survey 12 years ago. But La Trobe geneticist, Dr Danuta Loesch, says teenagers are not the only ones getting bigger.
Since measurements were first taken of convicts brought out from Britain 150 years ago, the average adult height has increased by six inches, male weight by almost five pounds and female weight by about seven pounds. Children under the age of 10, however, have not changed in size since the 1980s whereas adolescence appears to be the "major obesity zone", according to Dr Loesch.
She says the period of weight gain coincides with a surge of genetic effects on growth in height and weight. Another possible explanation is that teenagers are sensitive to environmental factors: if they eat the wrong food they may put on weight beyond normal limits.
The study found the level of exercise participation low, with only 6 per cent of teenage girls saying they took part in strenuous activities.
Dr Geraldine Naughton, a paediatrician at the Royal Children's Hospital in Melbourne, called on schools to take an integrated approach to children's physical health to prevent obesity. She urged physical education teachers to give children PE homework so they would be more active after school.