HAVING a fat father or grandfather makes you more likely to be overweight, according to new research.
And men planning to start a family need to lose their love handles three months before the conception date if they want to avoid fathering fat children.
While it has already been established that a mother's eating habits during pregnancy impact whether a baby will go on to have a weight problem, new research to be presented to an obesity conference in Canberra tomorrow, highlights the role of fathers in determining the health of their children.
The research by University of NSW Professor Margaret Morris was conducted in rats.
It found the grandsons of fat grandfathers fed a junk food diet ended up much fatter than the grandsons of lean grandfathers who were fed the same junk food diet.
It wasn't the rat's genes that made the difference, but the influence of the environment on their genes, Professor Morris said.
"The environment can change how our genes are expressed. Pollutants, obesity, even stress can alter how genes are expressed in offspring without altering the genetic code," Professor Morris says.
The good news is that the grandsons of fat grandads who consumed a healthy diet did not end up obese.
"This shows there are things you can do, if you have a healthy diet and exercise you can make a difference and overcome the effect of your grandparents," Professor Morris says.
The conference will hear evidence that couples planning a family need to get their weight in order 12 months before they conceive if they want to avoid having an obese child.
"We talk about the first four years of a child's life and that starts a year before the baby is born," says Professor Morris.
"You've got to start three months before you get pregnant, lose the weight before you conceive," she said.
Mothers also have to be careful not to put on too much weight during the pregnancy but losing weight during pregnancy could also make the baby obese, she said.
When there is less nutrition entering the womb it sends signals to the baby's developing fat cells that causes a chemical imbalance that can trigger weight problems in later life.
The obesity conference will also hear that Medicare is failing the fat because it doesn't pay for weight loss programs and is stingy in covering lap band surgery.
The head of Australia's Obesity Coalition Professor John Funder says it is "outrageous" that the public health system pays for just a small number of bariatric surgeries each year.
"People with chronic, relapsing and severe obesity should not have to wait many years for interventions that are proven not only to work, but also to save money in the short, medium and long term," he says.