Sitting Down Makes Your Bum Bigger, Study Shows

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Health News | Dec, 14 2011

Sitting around really does give you a big backside, scientists have revealed.

Researchers found that the pressure put on areas of the body used for sitting or lying down produces up to 50 per cent more fat in those parts.

This can explain why couch potatoes and other sedentary behavior makes you fat when combined with a lack of exercise.

But even those with healthy diet and exercise habits will be affected if they spend long periods sat behind a desk.

Researchers found that preadolescence cells – the precursors to fat cells – turn into fat cells and produce even more fat when subject to prolonged periods of ‘mechanical stretching loads’ – the kind of weight we put on our body tissues when we sit or lie down.

By studying MRI images of the muscle tissue of patients paralyzed by spinal cord injuries, they noticed that, over time, lines of fat cells were invading major muscles in the body.

This spurred an investigation into how mechanical load – the amount of force placed on a particular area occupied by cells – could be encouraging fat tissue to expand.

A team stimulated preadipocytes with glucose or insulin to turn them into fat cells. They then placed individual cells in a cell-stretching device, attaching them to a flexible, elastic substrate – or underlying.

The test group of cells were stretched consistently for long periods of time, representing extended periods of sitting or lying down, while a control group of cells was not.

The researchers noted the development of liquid droplets in both the test and control groups. However, after just two weeks of stretching, the test group developed significantly more – and larger – droplets.

By the time the cells reached maturity, the group that received mechanical stretching had developed fifty per cent more fat than the control group.

Professor Amit Gefen, from Tel Aviv University, said: “Obesity is more than just an imbalance of calories. Cells themselves are also responsive to their mechanical environment. Fat cells produce more triglycerides [the major form of fat stored in the body], and at a faster rate, when exposed to static stretching.

“There are various ways that cells can sense mechanical loading. It appears that long periods of static mechanical loading and stretching, due to the weight of the body when sitting or lying, has an impact on increasing lipid [fat] production.”

These findings indicate that we need to take our cells’ mechanical environment into account as well as pay attention to calories consumed and burned, said Professor Gefen.

He warned that, while there are extreme cases of people confined to wheelchairs or beds due to medical conditions, many people live a too sedentary lifestyle – spending most of the day behind a desk.

Even somebody with a healthy diet and exercise habits will be negatively impacted by long periods of inactivity.

The research has been published in the American Journal of Physiology – Cell Physiology.

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  1. Bruce Hirsch says:

    This article shares a fault with many published stories about scientific research: it goes way beyond what the research actually does to draw hopeful—but fanciful—conclusions. It is not at all true that the actual scientific research paper claims “Sitting around really does give you a big backside.” It is also not true that “Researchers found that the pressure put on areas of the body used for sitting or lying down produces up to 50 per cent more fat in those parts.”

    Making unfounded claims for research can cause difficulties for scientists and those who look to them for help. It can give hope to people when there is no reason for it, and cause them anguish. It causes people who do not know much about science to underestimate the amount of work and the dead ends that precede discoveries. And raising false hopes can make some people think that research is not worth supporting because it only leads to disappointment.

    Science journalists, like all other journalists, have a responsibility to make sure that they write only what is demonstrably correct, except when they point out the uncertainties or are clearly speculating.

    Here, in layman’s terms, is what the researchers actually reported. They raised adipocyte precursors (immature cells which are capable of developing into fat cells) in laboratory dishes. They were put into a device which stretched the surface the cells grew on, so the cells were subjected to a force known as tensile stress. They were kept alive and growing under this condition, under constant tensile stress, for three to four weeks. As a control (a comparison grown under identical conditions except for the phenomenon being tested) they grew other cells without stretching their growing surface.

    The idea was to see if constant stress caused the precursor cells to turn into fat cells faster than the control cells, and if the stressed cells produced more fat. They were investigating the idea that the relatively unchanging stress in the fat pad of people’s buttocks who sit at work for long periods of time could cause it to grow larger. If the cells growing in laboratory dishes did get larger or make more fat it would not mean that the same thing happens in us when we sit, but it could mean that this is an idea which should be looked at more closely.

    Sure enough, the cells grown on the stretched base did turn into fat cells more quickly, and they did produce more fat. Biochemical tests also verified that related events occurred at the molecular level.
    Nowhere in the article do the authors report doing any experiments at all on humans. All they say is, “Our present findings clearly indicate that a static (sustained) stretch accelerates lipid production in adipocytes, which could theoretically correspond, for example, to the increased adipose mass in the buttocks of obese individuals, where soft tissue stretching during weight-bearing is substantial” (emphasis added).

    The scientists also say, “Our present results may be the foundation of additional work that should be focused on monitoring the adipose conversion in more physiological conditions.” The term physiological conditions refers to the complicated interactions that take place in the bodies. Here are just a few examples of those interactions: in the buttocks there are many other cell types besides adipocytes; people do not sit immobile for weeks on end; there are muscles present which induce their own stresses in the region; fat cells respond to chemicals reaching them from other parts through the bloodstream; fat cells produce chemical themselves which affect other tissues.

    I think this is a very well done experiment, and I also think that the scientists who did it knew and understood just what it meant and what should be done next. The unnamed reporter either did not understand what he was reading, or cared more for drama than accuracy. And if this was based on a press release from Tel Aviv University, shame on them.