The year in which a person is born may predict whether they will become obese, a new study has found.

Doctors discovered year of birth affects the activity of a gene that could raise the odds of obesity.

People who show a mutation of a gene called FTO – dubbed the 'obesity gene' - are more likely to become overweight if they were born after 1942, scientists found.

Various studies have linked versions of the FTO gene to chronic obesit.

In May a U.S. study found the gene is thought to trigger hunger pangs and affect a person's ability to resist impulse eating.

Changes in culture, such as a greater reliance on technology and the availability of food may be boosting obesity by 'activating' the obesity gene, researchers theorised.

Wanting to investigate the impact of genes versus environment on traits such as obesity, researchers looked at the risk of obesity across generations.

They sought to find out whether different conditions experienced by different age groups might alter the expression of the variation of the FTO gene linked with obesity.

They used data from the Framingham Heart Study, which involved sequencing the DNA of more than 10,000 parents, children and grandchildren.

They also used data from participants in the Framingham Offspring Study, which followed children of participants in the original study.

This meant the team could determine which families carried the version of the FTO gene which is linked to obesity.

The study was not able to identify differences that combined with the version of the FTO gene to increase the risk of obesity.

But the authors suggested that post World War II factors such as an increased reliance on technology rather than manual labour and the availability of high-calorie processed food were contributing factors.

Lead author Dr James Niels Rosenquist, a psychiatrist at Massachusetts General Hospital, Boston, U.S., said: 'We know that environment plays a huge role in the expression of genes, and the fact that our effect can be seen even among siblings born during different years implies that global environmental factors such as trends in food products and workplace activity, not just those found within families, may impact genetic traits.'