Morbid obesity is on the rise.

Morbid obesity is on the rise. Photo: Jim Rice

Extreme obesity has increased to the point that people are losing sight of what a normal weight actually is, health experts say.

Morbid obesity, the highest scale of obesity, increased by 68 per cent between 1997 and 2008, a study of women living on the east coast of Australia has found.

The study found overall obesity levels increased by 30 per cent, in what doctors say is part of a nationwide weight gain.

Public Health Association of Australia president Heather Yeatman said messages about healthy eating and exercising more were falling on deaf ears because many did not even realise how risky their weight was.

''I think that people are not really aware of what normal weight is any more,'' Associate Professor Yeatman said. ''If you have got 60-plus per cent of people overweight or obese that has become normal viewing these days, not only for children but for parents as well.''

Professor Yeatman said people were sick of hearing about weight, and many did not even realise messages targeted them.

''We need to focus on the positive things people can do … the fact that everyone needs to improve their diet, eat more sustainably and improve their exercise,'' she said.

The researchers, from Deakin University, measured the height and weight of nearly 1500 women who participated in the Geelong osteoporosis study, avoiding the problems of inaccurate knowledge that often plagued researchers who simply asked people how much they weighed.

It found morbid obesity had increased from 2.5 per cent of the population to about 4.2 per cent, or just under one in 20 people.

Morbid obesity is defined as a body mass index of 40 or higher, and is linked to far higher risks of problems such as diabetes, cancer, and heart disease. Overall the study found nearly 30 per cent of participants were obese in measurements taken between 2004 and 2008, compared with 22.5 per cent of people measured between 1993 and 1997.

Study leader Julie Pasco, the head of the epidemiology unit for musculoskeletal and metabolic disorders at Deakin University, said the patterns seen in her study were likely to be occurring across the country.

This shift, which was not restricted to people of a particular age or socio-economic status, could indicate the whole population was shifting towards a greater risk for obesity-related disease.

On Thursday Obesity Australia launched a five-point plan to deal with the obesity epidemic. It included giving the parents of young children more information, expanding the Stephanie Alexander Kitchen Garden Programs in primary schools, and restricting television advertising of fast foods and high-sugar drinks.