They may look gorgeous with their round cheeks and roly poly bodies but experts warn that obese babies may face a lifetime of health problems mapped out even before conception.

Almost 60 per cent of women of child-bearing age in wealthy countries are overweight or obese, The Lancet reported in April.

Have your say on the childhood obesity epidemic. Email letters@sunherald.com.au

Medical researchers from the University of NSW have found that larger mothers tend to produce bigger offspring with hearty appetites who gain weight easily.

"We know that women are now more likely to be overweight or obese when they get pregnant," Professor Margaret Morris of the university's faculty of medicine said.

"It does have consequences for offspring because we know that the child's body mass index is correlated with their mother's body mass index. Mothers are getting bigger; babies are getting bigger."

In Professor Morris's studies on rats, babies born to obese mothers consumed more food and readily bulked up.

"The offspring of the obese mums put weight on more quickly than the babies of the lean mums," she said.

"We also found that they had stronger appetites and ate more energy than the pups of the lean mothers."

A British study showed that female rats given a diet of junk food produced babies with a preference for the same.

And it is not just the mother's diet that plays a role.

Researchers at the University of New South Wales also found that male rats on a high fat diet sired babies that were more likely to develop diabetes.

"Having a fat dad affected the baby rat's pancreas so it was unable to respond normally to glucose - they were on their way to diabetes," Professor Morris said.

"It's one of the first demonstrations that an environmental factor in the father might be transmitted to its offspring."

While the idea of being genetically programmed to be obese is a frightening one for many, the researchers also found that diet and exercise could mitigate the risk of obesity.

"When we took the offspring of the fat mums and gave them an exercise wheel, we got beneficial effects from exercise," Professor Morris said.

"Voluntary exercise can reverse some of the metabolic effects of having come from a fat mum.

"We had another study where we put the offspring of obese mums on a healthy diet. The offspring on a healthy diet were much better off than those who had an unhealthy diet.

"I think the message is: what you are doing today has an impact and everyone can do that, provided they have the information and the wherewithal to buy healthy food."

More research needed to be done on humans in this area, Professor Morris said.

The Sun-Herald's Healthy Habits campaign, launched on Sunday, revealed that it was not asthma nor food allergies that Australian parents needed to worry about the most: the most common chronic health disorder in young people was now being overweight or obese, the Australian Medical Association and Obesity Policy Coalition said.

Almost a quarter of Australian children are overweight or obese and doctors fear if the trend continues this generation of children will die younger than their parents.

The 10-week campaign, supported by The Children's Hospital at Westmead, will run to the end of January and cover critical topics including body image, the "pester power" of children, sedentary lifestyles, urban design and the difficulties of diagnosing obesity.

It also provides families with seven practical steps - created by weight management experts at the hospital - to become more active and aware of their food choices.

In pregnancy, one of the most serious risks of obesity is gestational diabetes, which has increased three-fold in Australia over the past 20 years.

According to figures from the Australian Institute of Health and Welfare, about one in 20 women is affected by the condition, which results in an increased rate of still birth, premature delivery, surgical intervention during labour and higher birth weight.

In areas of Sydney such as Liverpool, about 12 per cent of expectant mothers develop gestational diabetes.

The diagnostic criteria for gestational diabetes will change next year leading to a substantial increase in the number of women affected.

A research team at Royal Prince Alfred Hospital has had some success with controlling the diets and lifestyles of women with gestational diabetes.

The chairwoman of International Maternal and Child Health at the University of Sydney Professor Heather Jeffery has been measuring the body fat of newborns at the hospital in a device called a Pea Pod.

She observed that if the women affected by gestational diabetes made improvements to their diets and exercised regularly, their babies were born at normal weight.

"I think what we can do in the community of health providers is say that, if you do have your women well controlled, you have better outcomes," she said.

"We also know if you control them well the mothers have less likelihood of going to type 2 diabetes. If they are not controlled, they have a about a 30 per cent chance of developing type 2."

A woman's weight problem does not have to be a life sentence for her baby.

"The whole story is one which really starts at preconception," Professor Jeffery explained.

"The message has to be that they have to be close to a healthy weight when they go into pregnancy, they have to control their diets when they are pregnant, then they need to be encouraged and supported with breastfeeding once their baby is born.

"There are a number of different stages where you can intervene to improve outcomes."

The Sun-Herald