couch potato 311.
(photo credit: Thinkstock/Imagebank)
It’s not just that you are avoiding exercise and scarfing down pretzels. By allowing you posterior to carry the full load of your body for hours on end you are actually stimulating your fat cells to multiply. Lying down and spreading the burden of your weight across the full length of your body eggs on even more fat cells.
That is the surprising conclusion of research conducted at Tel Aviv University, which found that the static stretching created by a person’s weight when he or she is sitting and lying down encourages the body to create new fat cells. More specifically, it causes preadipocyte cells —the precursors to fat cells — to turn themselves into fat cells faster.
“Often when we think about obesity or gaining weight, we think about consuming more food than we can burn in calories,” Amit Gefen, of the university’s biomedical engineering department, told The Media Line. “What this research tells us is that it’s not only nutritional balance – the equation of how many calories you put in and how many you burn – but that there is mechanical element as well.”
Obesity rates worldwide have doubled in the last three decades, rising from about 5% of men and 8% of women in 1980 to 10% and 14%, respectively, by 2008 and creating a range of health problems including cardiovascular disease, cancer and diabetes. But Gefen wasn’t motivated to carry out his research by the horizontally challenged.
He was studying the problem of people who are bed-ridden or wheelchair bound due to disease or disability, and typically suffer atrophying muscles from their prolonged inactivity. Examining MRI images of patient muscle tissue, Gefen noticed that over time fat cells were invading major muscles. This suggested that mechanical load – the force placed on an area by weight on the cell – could be encouraging fat tissue to expand.
“What you see in their tissue is the replacement of muscle tissue by fat,” said Gefen. “You start seeing stripes of fat going from the fat layer into the muscle layer until the muscle layer is gone. We believe there is something of mechanical environment of cells and tissues that stimulates fat to invade muscle and stimulates muscle to retreat.”
To test that hypothesis, Gefen and his graduate student Naama Shoham placed individuals preadipocyte cells on a flexible elastic substrate attached to a cell-stretching device.
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The cells were all given glucose or insulin to stimulate them into becoming fat cells, but one group was subject to long periods of stretching that mimicked the effect of lying or sitting down while a control group was not. Both groups developed lipid, or fat, droplets, but after only two weeks the stretched cells developed significant more and larger lipid droplets.
By the end of the study, which was published in the American Journal of Physiology
— Cell Physiology this month, the stretched cells had 50% more lipid droplets. It appears, Gefen said, that cells can sense mechanical loading and that triggers chemical processes.
Practically speaking, the results show that even people who eat well and exercise will see some of the benefits of their healthy lifestyle undone if they also go through long periods of inactivity, like hours sitting at a desk. For those committed to a lethargic lifestyle, getting up from your swivel chair or living room sofa and walking around may help alleviate the impact of mechanical loads, Gefen said.
Elastic substrates are not the same as the human body, which is more complex and three dimensional (in the case of couch potatoes exceptionally three dimensional). So Gefen’s next study, which he estimates will take two to three years to complete, aims to more closely mimic the human body.
Gefen and his fellow researchers will also be investigating how long a
person can sit or lie down without the mechanical load becoming a factor
in fat production.
The goal of the studies is to create models researchers can use to
better understand obesity and its causes. Such models can be used in the
early stages to test the efficacy of new drugs or medical devices
without using animal studies and before they are subject to clinical
trials with humans.
Gefen’s team also included Ruth Gottlieb, Uri Zaretsky and Orna
Shaharabani-Yosef from the biomedical engineering department and Dafna
Benayahu from the Department of cell and developmental biology.
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