A new research study suggests that a man's weight affects the genes in his sperm, Independent reports.

The link was discovered when researchers examined the sperm of lean and obese men, as well as those undergoing weight-loss surgery. Researchers found that heritable chemical changes that can switch genes on or off differed between the three groups.

Even though the exact effects of these chemical changes are unknown, it is believed that they influence the DNA linked to the control of appetite. This may explain why children of obese fathers are vulnerable to being overweight.

Scientists believe this could be one explanation for why children of obese fathers are also vulnerable to being overweight.

Lead scientist Dr Roman Barres, from the University of Copenhagen in Denmark, said: "Our research could lead to changing behaviour, particularly pre-conception behaviour of the father.

"It's common knowledge that when a woman is pregnant she should take care of herself - not drink alcohol, stay away from pollutants, etc - but if the implication of our study holds true, then recommendations should be directed towards men, too."

The new research was published in the journal Cell Metabolism.

The research team is now working with a fertility clinic to study epigenetic differences in discarded embryos produced from the sperm of men with varying body weight.

Fertility expert Professor Allan Pacey, from the University of Sheffield, said: "This is an interesting study which provides further evidence to support the theory that some characteristics can be passed by sperm from a father to his children, without altering the basic structure of the genetic code.

"Whilst the study examines a relatively small number of individuals, the fact that such significant differences can be found in the epigenetic markers of lean and obese men is intriguing and, in my opinion, worthy of more detailed investigation.

"In addition, the fact that changes can be seen in men before and after significant weight loss also adds some validity to the findings."