Obesity is in the genes.
A new study shows that 43 per cent of healthy people at the greatest genetic risk of obesity developed the condition over a five -year research period, compared to just 13 per cent in the lowest-risk group.
US experts say that the "new and important" findings show that those vulnerable to obesity will need to walk more than 2,200 extra steps per day to keep the weight off.
Dr. Evan Brittain, of Vanderbilt University Medical Center in Nashville, said: "You can imagine a future in which the data could form the basis of an individual's physical activity recommendation from their doctor.
"I think these findings could be empowering for patients because the current physical activity guidelines take a one-size-fits-all approach.
"What we learned is that depending on your genetic risk, the guidelines may underestimate the amount of activity needed to reduce your risk of obesity.
"Most importantly, I would like for patients to know that your genetic risk doesn't determine your overall risk of obesity, and you can actually overcome that risk by being more active."