Number of fat cells cannot be reduced.

• Position: YOUR LIFE

Radioactive carbon-14 produced by above-ground nuclear testing in the 1950s and 1960s has helped researchers from Lawrence Livermore (Calif.) National Laboratory determine that the number of fat cells in the human's body--whether the individual is lean or obese--firmly 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 its various accompanying diseases, including high blood pressure and diabetes.

Carbon dating typically is used in archeology and paleontology to determine the age of artifacts. However, in this application, scientists used the pulse of radiocarbon to analyze fat cell turnover in humans.

Radiocarbon or carbon-14 is produced naturally 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, but atmospheric testing of nuclear weapons from 1950-63 produced a global pulse in the amount of radiocarbon in the atmosphere.

In his study, LLNL scientist Bruce Buchholz analyzed the uptake of carbon-14 in genomic DNA within fat cells to establish the dynamics of...