Lifestyle and exercise

'Couch potato' lifestyle linked to bigger bums

"It's official: Sitting around really does give you a fat behind," the Mail Online reports. While this may seem logical, it should be pointed out that the study behind the headlines involved mice, not humans.

The website reports on a laboratory study that used special microscopic techniques to measure the stiffness of fat cells (adipocytes) and how this stiffness reacts to mechanical stress.

The results suggest that prolonged mechanical stress – such as spending a lazy Sunday sitting on the sofa watching a box set – could increase the stiffness of fat cells. This could then influence their development, possibly leading to a bigger backside.

But because of the highly artificial methods used by the researchers, the Mail's conclusions – as commonsense as they may seem – are not supported by the evidence provided in the study.

Where did the story come from?

The study was carried out by researchers from Tel Aviv University in Israel, and was supported by a grant from the Israel Science Foundation and the Israel Ministry of Science, Technology and Space.

It was published in the peer-reviewed scientific journal, Biophysical Journal.

Most of the evidence reported by the Mail Online was not covered by the research study, but was mentioned in an accompanying press release.

The research team published a similar study covered by Behind the Headlines in 2011.

The Mail Online deserves a red card for failing to report at any point in their story (at least at the time of writing) that the current study did not involve humans.

What kind of research was this?

This was a laboratory study that used special microscopic techniques to measure the stiffness of adipocytes, which are cells that store fat.

The researchers report that 70% of the US population now meets the definition for being overweight or obese. They say that while it is recognised that the excess accumulation of body fat occurs when energy intake exceeds nutritional requirements, there is also "increasing evidence that lipid [fat] production in adipocytes is significantly affected by their mechanical environment".

Previous research is said to have suggested that cyclical stretching or vibration suppresses the formation of fat cells, while static stretching (presumably as may occur when sitting) accelerates it. 

The researchers say that adipocytes influence the mechanical environments of their neighbouring cells, applying distorting forces and stresses on each other when the tissue is weight bearing.

They therefore say that determining the mechanical properties of adipocytes, and the intracellular structures within these cells, is important. How you use your body – not just in terms of exercise, but also how you position it – may therefore have an effect on fat levels.

What did the research involve?

The research involved preparing cultures of adipocyte cells that were at an early stage of development.

The researchers then used special microscopy techniques of atomic force microscopy (AFM) and interferometric phase microscopy (IPM) to measure the stiffness within the cells.

These are advanced microscopy techniques that allow researchers to "zoom in" at a nano level, a resolution so detailed that individual molecules can be studied.

Using AFM, they calculated the shear stiffness around the nucleus of the cell and around the lipid (fat) droplets in the cell, which was termed the "effective stiffness". The researchers then used IPM to measure the distribution of stiffness within the cell. They verified their results using a technique called finite element simulations.

What were the basic results?

The results basically demonstrated that the lipid droplets within a fat cell are stiffer than cytoplasm (the thick jelly-like substance that fills a cell). The lipid droplets within a cell were found to mechanically distort its environment.

How did the researchers interpret the results?

The researchers conclude that their study provides evidence that adipocytes (fat cells) stiffen as a result of the accumulation of lipid (fat) droplets.

They say that, "Our results are relevant to research of adipose [fat]-related diseases, particularly overweight and obesity, from a mechanobiology and cellular mechanics perspective."


The researchers refer to the results of previous studies, which suggested that placing prolonged mechanical stress upon fat cells – such as making them bear weight through sitting on them for prolonged periods – leads to the development of fat cells.

Results from this study suggest that as fat cells develop and accumulate fat droplets, they change in stiffness. This could lead to a change in the stiffness of the overall fat tissues, thereby changing the stresses experienced by other fat cells and influencing their development.

Despite the limitations of this study – not least that it did not involve humans – its results add further weight to the argument that a sedentary lifestyle is not good for you. 

Current activity recommendations advise that adults aim to be active every day, taking at least 150 minutes (2½ hours) of moderate intensity activity in bouts of 10 minutes or more every week, or 30 minutes on at least five days a week. All people are advised to minimise the amount of time spent sedentary (sitting) for extended periods.

NHS Attribution