Inheritable traits GSO Images/Getty

Blame grandpa. A study in mice shows that the grandsons of obese males are more susceptible to the detrimental health effects of junk food, even if their fathers are lean and healthy.

The finding adds to evidence that new traits can be passed down the family line without being permanently recorded in a family’s genes – a phenomenon called transgenerational epigenetics.


Last year, a study found that the DNA in the sperm of obese men is modified in thousands of places, and that these sperm also contain short pieces of RNA. These are epigenetic modifications – they don’t affect the precise code of genes, but instead may affect how active particular genes are.

Now Catherine Suter at Victor Chang Cardiac Research Institute in Sydney and her team have investigated the longer-term effects of paternal obesity. To do this, they mated obese male mice with lean female mice.

They found that, compared with the offspring of lean males, both the sons and grandsons of the obese males were more likely to show the early signs of fatty liver disease and diabetes when given a junk food diet. The same effect wasn’t seen in daughters or granddaughters.

Even when the sons of the obese males were fed a healthy diet and kept at a normal weight, their sons still had a greater tendency to develop obesity-related conditions when exposed to a junk diet.

Sperm secrets

However, the effect didn’t seem to be passed on to great-grandsons. “This is good news because it suggests that the cycle of obesity can be broken,” says Suter.

As the effect disappears after two generations, Suter suggests the susceptibility to junk food is passed on by epigenetic effects. Her team’s research hints that small pieces of RNA in the sperm could be to blame, with these possibly influencing how a male embryo develops.

Romain Barrès at the University of Copenhagen, who published the obese men study last year, agrees that small pieces of RNA may be involved in obesity transmission. In a similar experiment, his team found that high-fat diets were associated with reduced birth weight – a factor that may be linked to obesity in later life – in male rats’ sons and grandsons, and that this also correlated with changes in the levels of small RNA pieces. “We share the same observations on paternal transgenerational inheritance,” he says.

Suter’s study isn’t the first to report the inheritance of a vulnerability trait from a grandfather. In 2013, male mice were found to shudder when they sniffed a specific fragrance that their grandfather – but not their father – had been conditioned to associate with receiving an electric shock.

Studies like these underscore the importance of men’s health at the time of conception, says Suter. “A baby’s health has long been considered the mother’s responsibility, but little attention has been paid to the father’s health.”

Journal reference: Molecular Metabolism, DOI: 10.1016/j.molmet.2016.06.008

Read more: First evidence that sperm epigenetics affect the next generation