Even After Weight Loss, Fat Cells Remain

May 5, 2008— -- There might be new vindication for those who claim the "big-boned" defense for being overweight, a new study shows.

Adults have about the same number of fat cells in their body constantly, even after losing a significant amount of weight, Swedish researchers say.

Researchers at the Karolinska Institute in Stockholm, Sweden, made their determination by studying fat samples from liposuction and abdominal reconstruction surgery in lean and obese volunteers, leading them to conclude that the number of fat cells is determined in childhood.

The researchers made their discovery by studying levels of radioactive materials locked inside of fat cells in people who had lived through the period of Cold War nuclear bomb testing from 1955 to 1963.

People whose fat cells developed before the onset of testing still had radioactive matter in the cells, showing that their fat cells were being replenished. The researchers were able to estimate that the body replaces cells at a rate of roughly 10 percent a year.

The fact that fat cells are constantly dying and being replaced could potentially offer an opportunity to develop new anti-obesity therapies, the researchers wrote in their study, which was published Sunday in the journal Nature.

Lead study investigator Kirsty Spalding said that because the study highlights the fact that fat cell population in humans is dynamic -- as in, our fat cells are consistently dying and being replaced with new fat cells -- researchers should now focus on developing weight-loss drugs that modulate the number of fat cells so that there is more cell death than cell growth.

"Potential treatments could change the balance of the birth rate and death rate of fat cells, and could compensate loss by decreasing the overall number of fat cells to help keep this weight off," Spalding explained. "Or we could develop therapies to affect this balance in the opposite direction, like to aim therapies at increasing the number of fat cell growth in cancer patients."