It’s official: sitting on your tuchus all day will make you fat. How do we know? A team of researchers at Tel Aviv University say so.

Their findings may not exactly come as a surprise but they have spent the past two years making sure as part of a four-year study into obesity.

It’s all to do with the way prolonged periods of sitting still allows a build-up of fats in our rear ends.

“People have been saying this for ages. But now we have the science to prove it,” said Prof Amit Gefen from the university’s department of Biomedical Engineering.

“Obesity is not just about what you eat. Until now science has focused on the nutritional links between what you eat and how fat you are.

“But it is also about how fat cells respond to everyday forces and how they react to those forces over time.

“Fat cells that are exposed to sustained, and chronic pressure, such as when you’re sitting down, experience an accelerated growth of lipid droplets, which are the molecules that carry fats.

“It is the pressure of increased weight and loading in the tissues of the buttocks that makes it fatter.

“It is a domino effect. By sitting down all the time the pressure applied on your bum increases the fat cells size.

“As the cells become bigger, they become stiffer and that causes them to produce more fat.”

So what is the secret to avoiding the couch potato bottom?

“Make sure you get up and walk around every half an hour or so,” he said. “Make a cup of tea, and stretch your legs.

“Don’t sit on your bum all day long or the fat cells increase by up to 50 per cent. Sitting for a long period has always been bad for you but now we know it encourages the development of fat we can work to prevent it.”

Prof Gefen and his colleagues are the first to describe this cycle of obesity and made their discovery with funding from the Israel Science Foundation. He hopes the findings will go some way to developing treatments.

“Now we know how the cells behave we can use that to develop the technology to prevent the fat expanding. The science is not there yet, but you could be sat at your desk with a chair that vibrates the cells in your bottom.

“The vibrations could help stop the promotion of more fat cells. We saw a sense of it last year with the machines that vibrate in the gym.”

A 2012 NHS survey found that just over a quarter of all adults in England are obese. The NHS spends £6 billion a year treating diseases caused by poor diet and sedentary lifestyles.