Newly-released research out of the UK has found if your grandfather smoked, it could affect how much body fat you have.
The 'Children of the 90s' study - a long-term health research project at the University of Bristol - enrolled more than 14,000 pregnant women in 1991 and 1992.
It followed the health of parents and their children through the generations and was recently extended using newly collected data on grandfathers and great-grandfathers of study participants.
It found the granddaughters of men who smoked before the age of 13 carry 3.54kg more fat compared to those whose ancestors began smoking after that age.
The study suggested the results could be caused by smoking altering DNA in older generations, which could then be inherited by their descendants.
"First, that before puberty, exposure of a boy to particular substances might have an effect on generations that follow him," Professor Jean Golding said.
"Second, one of the reasons why children become overweight may be not so much to do with their current diet and exercise, rather than the lifestyle of their ancestors or the persistence of associated factors over the years."
Prof Golding said more research would need to be done to confirm these observations.
"If these associations are confirmed in other datasets, this will be one of the first human studies with data suitable to start to look at these associations and to begin to unpick the origin of potentially important cross-generation relationships," she said.
Previous research from the same study found that if a father started smoking before the age of 11, his sons would carry more body fat than expected.