Until now it has been the general notion that adults can not make new fat cells. Instead, it has been assumed, they increase their fat mass by incorporating more lipids into already existing fat cells in order to settle their body weight (lean, overweight, obese). However, an international team of researchers, lead by Kirsty Spalding, Jonas Frisén and Peter Arner at the Swedish medical university Karolinska Institutet, has recently shown that adult humans constantly produce new fat cells irrespective of their body weight status, sex or age.

“The total number of fat cells in the body is stable overtime, because the making of new fat cells is counterbalanced by an equally rapid break down of the already existing fat cells due to cell death”, says Peter Arner, Professor at the Department of Medicine, Huddinge.

The study has been made possible due to the use of a combination of two unique procedures. First, the authors could determine the age of the fat cells in the body by measuring the incorporation of radioactivity from the atmosphere into the genetic material (DNA) of the fat cells. Second, they compared the size of the fat cells in relation to the total amount of adipose tissue in a very large number of human subjects with a large individual variation in body weight.

The researchers also shows, that obese subjects make about twice as many new fat cells per year as lean ones, and following have a twice as high cell death in comparison to the lean. Even if obese subjects are subjected to market weight reduction they keep the total number of fat cells in the body constant, but the size of individual fat cells is decreased markedly. The findings therefore provide a new target for treatment of obesity, namely by attacking the signals and genes in fat cells that control the formation of new such cells.

“The results may, at least in part, explain why it is so difficult to maintain the weight after slimming”, says Peter Arner. “The new fat cells generated during and after weight reduction need to fill up their lipids rapidly.”

Publication: ‘Dynamics of fat cell turnover in humans’, Kirsty L. Spalding, Erik Arner, Pål O. Westermark, Samuel Bernard, Bruce A. Buchholz, Olaf Bergmann, Lennart Blomqvist, Johan Hoffstedt, Erik Erik Näslund, Tom Britton, Hernan Concha5, Moustapha Hassan, Mikael Rydén, Jonas Frisén & Peter Arner, Nature AOP, 4 May 2008.

For further information, please contact:

Professor Peter Arner
Tel: +46 (0)8-58582342 or +46 (0)70-5798121
Email: peter.arner@ki.se

PhD Kirsty Spalding
Tel: +46(0)70-4371542
Email: Kirsty.Spalding@ki.se

Press Officer Katarina Sternudd
Tel: +46 (0)8-524 838 95 or +46(0)70-224 38 95
Email: katarina.sternudd@ki.se

Karolinska Institutet is one of the leading medical universities in Europe. Through research, education and information, Karolinska Institutet contributes to improving human health. Each year, the Nobel Assembly at Karolinska Institutet awards the Nobel Prize in Physiology or Medicine. For more information, visit ki.se