Fat future: According to figures cited in the study, most obese adults have been obese since childhood.

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SYDNEY: Whether you lose weight or pile on the pounds, the number of fat cells in your body remains constant throughout adult life, say Swedish researchers who have found evidence that our quota of fat cells is set during adolescence.

The controversial findings, suggest that our weight during childhood affects how fat we are later in life and also offer an explanation of why some adults find it so difficult to remain slim after losing weight.

Childhood obesity epidemic

The research, detailed today in the U.K. journal Nature reveals that when adults gain weight, the fat cells, or adipocytes, that they already have enlarge, rather than increase in number, and conversely that these fat cells shrink during weight loss.

"Understanding the dynamics of adipocyte turnover in adults who have been obese since childhood is of great importance, especially given the current trend for an increase in childhood obesity," write the authors.

Led by Kirsty Spalding of the Karolinska Institute in Stockholm, they measured the number of fat cells in 595 individuals before and after major surgery – involving the reduction of the stomach – to reduce weight loss. While the treatment caused significant weight loss, and a decrease in the volume of fatty tissue, tests two years later revealed that there was no significant reduction in the number of fat cells within that tissue.

Spalding's team also found that though fat cells remain constant in number, they undergo a constant process of death and renewal; with around 10 per cent replenished every year and a total of 50 per cent replaced after eight years.

The researchers determined the age of the adipocytes by measuring the level of radioactive carbon-14 that they contained. Levels of carbon-14 in the atmosphere have increased since nuclear weapons testing in the mid-20^th century, and the proportion of carbon isotopes in cells can be used to indicate the year in which they were first formed.

Fat cell dynamics

The scientists argue that the finding could lead to the development of new fat-busting drugs that work by intercepting the process of death and renewal, to prevent the formation of new fat cells.

"This is the first paper which has attempted to determine the dynamics of fat cell number and volume in human fat tissue," said Louise Hutley, a fat cell biologist from the University of Queensland's Diamantina Institute in Woolloongabba, Australia.

"[The findings] could lead to new therapies down the track, but not right now," said Hutley. "The bottom line for people to take away from this study is that you need to educate yourselves about how you get fat. People need to eat less and do some physical activity each day throughout life."

According to figures cited in the study, most obese adults have been obese since childhood – and though less than 10 per cent of children with normal weight go on to develop adult obesity, over three-quarters of obese children go on to become obese adults.