Obese fathers can pass on poor metabolic health to the next generations before they are even born, Sydney researchers have found.

Scientists from Sydney's Victor Chang Institute and Garvan Institute of Medical Research together found obesity in fathers can be passed down to not only their children, but also future generations.

Using mice, the study published in the journal Molecular Metabolism, found offspring of obese fathers developed health problems, such as greater risk of metabolic disease, quicker when fed an unhealthy diet.

Lead author of the study, Victor Chang Institute's Dr Jennifer Cropley, said the findings could help explain the rise in diabetes, heart disease and obesity in humans.

"Overweight and resistant fathers, can actually pre-dispose their own offspring to develop metabolic syndrome themselves," Dr Cropley said.

"Mothers often get a bad wrap, especially overweight mothers ... the role of the father has been, until very recently underappreciated in the health of offspring.

"It's become that if fathers are overweight that can actually affect the health of their offspring."

Dr Cropley said the research group also wanted to find out how long that impact lasted.

The study used families of mice to carry out "foetal programming" research. ( File: ABC )

"So we took the offspring from overweight fathers [mice] and they had children themselves. We found that the grandchildren of the overweight fathers were also pre-disposed to develop metabolic syndrome — that is type 2 diabetes," she said.

But the question of exactly how these predispositions are passed along remains unanswered.

"The fascinating thing is it's not quite the DNA — the mice we used were all genetically identical so the genes passed from father to son were the same in each case," Dr Cropley said

"So the mechanism of what's perpetuating this predisposition to disease is actually a mystery."

"Obviously it's something that has to go through the sperm because the sperm is what is passed from father to child.

"Until recently it was thought that all that was in sperm was DNA, the genes, but we're starting to realise that there are other molecules in there as well."

"We found changes in very small molecules called non-coding RNA inside the sperm of obese dads and we think that might be what's perpetuating this disease risk from generation to generation."

Dr Cropley this kind of "foetal programming" of diseases translates well from mice into humans.

"I don't think it would be surprising if the same thing were happening in human beings, and perpetuating this familial cycle of obesity that we're starting to see, where whole families become entrenched in a cycle of obesity and metabolic syndrome for several generations," she said.

The focus now is on determining the transmitting mechanism.

"If we can find molecular changes in the sperm of these mice, we can then maybe go and have a look for the same sorts of molecular changes in human beings and ask whether the same sort of thing is happening, and hence whether the same kind of predisposition might be being passed on. That's the next step," she said.