A study carried out by University of New South Wales researchers showed that if fathers and grandfathers ate a high fat diet and were obese, their grandsons were more likely to be overweight.
Research conducted on rats, led by Professor Margaret Morris, found that sons and grandsons of fat fathers had worse outcomes than those of lean males, even if they were on the same diet.
While the effects of a mother's diet during and even before pregnancy are known, Professor Morris said the new research is a wake-up call for prospective dads.
"We know the mother's role is critical in terms of their own health and the health of a gestating baby, but the father's role has been pretty well neglected until quite recently," Professor Morris told The Weekly.
"We tend to think that a father could contribute his genes and that's about it, but this suggests both parents lifestyles may contribute to their babies genes."
The study, to be presented at the Obesity Summit in Canberra today, found that changes could be reversed if the father exercises and address unhealthy habits before and during pregnancy.
"People can optimise their chances by getting in shape and being as fit as they can and eating as well as they can," Professor Morris said.
"Obviously we need to encourage healthy lifestyles."
The intergenerational impact of an unhealthy diet was unmasked in rats during the study, but researchers say it is highly likely the results are relevant to humans.
The findings have sparked demand for further studies on the impacts of both parents behaviour on children during pregnancy.
"It's very hard to study intergenerational effects of obesity, and these findings are a good start," she said.
"We need to follow these patterns in humans, we need to give people the advice they need and we need to make sure children have the best start to life as possible."