New technique determines the number of fat cells remains constant in all body types

LIVERMORE, Calif. - The radioactive carbon-14 produced by above-ground nuclear testing in the 1950s and '60s has helped researchers determine that the number of fat cells in a human's body, whether lean or obese, is established during the teenage years. Changes in fat mass in adulthood can be attributed mainly to changes in fat cell volume, not an increase in the actual number of fat cells.

These results could help researchers develop new pharmaceuticals to battle obesity as well as the accompanying diseases such as high blood pressure and diabetes.

A new study by Lawrence Livermore National Laboratory scientist Bruce Buchholz - along with colleagues from the Karolinska Institute in Sweden; Humboldt University Berlin, Foundation of Research and Technology in Greece; Karolinska University Hospital; and Stockholm University - applied carbon dating to DNA to discover that the number of fat cells stays constant in adulthood in lean and obese individuals, even after marked weight loss, indicating that the number of fat cells is set during childhood and adolescence.

Carbon dating is typically used in archaeology and paleontology to date the age of artifacts. However, in this application, which appeared in the May 4 early online edition of the journal Nature, the scientists used the pulse of radiocarbon to analyze fat cell turnover in humans.

Radiocarbon or carbon-14 is naturally produced by cosmic ray interactions with air and is present at low levels in the atmosphere and food. Its concentration remained relatively constant during the past 4,000 years, butatmospheric testing of nuclear weapons from 1950-1963 produced a global pulse in the amount of radiocarbon in the atmosphere, Buchholz said.

In the new study, Buchholz analyzed the uptake of carbon-14 in genomic DNA within fat cells to establish the dynamics of fat cell turnover. Approximately 10 percent of fat cells are renewed annually at all adult ages and levels of body mass index.

Neither fat cell death nor its generation rate is altered in early onset obesity, suggesting a tight regulation of the number of fat cells in obese adults.

“Fat cells change in size but no one had ever measured fat cell turnover,” Buchholz said. “An increase in cell size means it can hold more mass.”

Obesity is increasing in epidemic proportions in most countries and poses a public health problem by enhancing the risks for cardiovascular diseases and metabolic disorders such as type 2 diabetes. According to the Centers for Disease Control and Prevention, the prevalence of overweight and obesity has increased sharply for both adults and children since the 1970s. Data from two National Health and Nutrition Examination surveys show that among adults aged 20-74 years the prevalence of obesity increased from 15 percent (in the 1976-80 survey) to 32.9 percent (in the 2003-04 survey).