The children of overweight men may be at greater risk of obesity due to genetic changes carried in their father’s sperm, a study suggests.

Scientists found a pattern of genetic markers in the sperm of obese men that have the potential to affect brain development and appetite control. The changes were absent in the sperm of lean men.



The finding is tentative, but if a risk is confirmed in larger studies, it will boost advice for men that getting in shape before they start a family could improve the health of their children.



“We don’t yet know if this is important. But if what we’ve found is transmitted to children and is doing something negative, it raises new questions about what do we need to do, and how long we need to do it before we conceive,” said Romain Barrès who led the study at the University of Copenhagen.

A person’s risk of obesity is heavily influenced by the genes they inherit and the environment they live in. The combination of factors leads to childhood BMI rising in line with parental weight, surveys have found. Previous work with twins shows that up to 70% of the differences between people’s fat mass is down to their DNA.

The Danish group looked at so-called epigenetic information contained in the sperm of 10 obese men and 13 lean men. The information is not encoded in DNA, but in other chemicals that work with DNA, such as methyl molecules that can attach to specific genes and silence them.

Facebook Twitter Pinterest Sperm from obese and lean men carry different biochemical markers that alter the activity of genes and can be inherited. Genes controlling brain development and appetite are thought to be most affected. Photograph: Donkin and Versteyhe et al./Cell/PA

After comparing epigenetic marks on sperm from the two groups of men, the researchers drew up what they believe is a “distinct epigenome that characterises human obesity.” Some of the changes they spotted alter genes involved in behaviour and eating “and could participate in predisposing the offspring to obesity,” they write in the journal Cell Metabolism.



The scientists next looked at epigenetic information carried by the sperm of six morbidly obese men before and after gastric bypass surgery to reduce their weight. They found that a week after surgery, the epigenetic markers on 1509 genes had changed in the men’s sperm, rising to 3,910 a year after surgery. More than half of these also differed between obese and lean men. Given the small size of the study though, the findings are far from conclusive.



The researchers are unsure if the epigenetic markers they found are passed onto children, and what effects they might have if they are. Most epigenetic information carried by sperm is erased during fertilisation. Though some survives, it is unclear how important it is for the next generation. Barrès said his team plans further studies to investigate, using sperm from obese fathers and IVF embryos they have donated after completing their families.

Wolf Reik, head of epigenetics at the Babraham Institute in Cambridge said that studies in animals have shown that changes in nutrition can alter the epigenetic markers carried by sperm. “It’s totally unknown what happens to these marks after fertilisation. In some ways the signals need to survive the global wipeout system, which is why it’s even more remarkable,” he said. “How strong the effects are in human populations is totally unknown. It’s impossible to tell at this point. That’s why the study is provocative, but much more needs to be done.”



Allan Pacey, professor of andrology at Sheffield University, said the study was intriguing and worthy of further investigation. But he added that it was too early to say what the observations meant for human health. “Until we know more, would-be parents should just aim to be as healthy as possible at the time of conception and not be drawn to faddy diets or other activities in order to try and influence the health of their children in ways we don’t properly understand.”