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2008-06-03 12:05:44
Rachel Mahan
LiveScience Staff Writer
LiveScience.com Fri May 30, 12:21 PM ET
Want to get rid of some fat cells as you age? Fat chance.
You're stuck with the number of fat cells you have acquired by about age 20, a
new study finds.
Researchers have known that people gain and lose weight at least in part by
changing how much fat is in their fat cells. The new finding is particularly
important for obese people, who the researchers say can have twice as many fat
cells as their lean counterparts.
The finding also suggests that obesity in adulthood is at least partly
determined by diet and exercise in childhood.
Strange study
To determine the age of fat cells in 35 subjects, researchers focused on a
marker found in fat cells - radioactive carbon from above-ground nuclear bomb
tests in the 1950s and 60s. More of a naturally occurring but rare type of
carbon, called carbon-14, was produced during the testing.
Bruce Buchholz, a chemist at Lawrence Livermore National Laboratory in
Livermore, Calif., explained how his team used this marker to make their
discovery.
Our bodies incorporate carbon-14 from the food we eat, along with the vastly
more abundant types called carbon-12 and 13. Since carbon-14 from the testing
is decreasing with time as it mixes with the oceans, the amount of rare
carbon-14 that a cell has taken up is like a timestamp for when the cell
formed, Buchholz said.
The researchers knew that cells were dying and being replaced over time,
because people born before the nuclear testing had fat cells that were created
after the testing. The scientists also found that about 10 percent of fat cells
were replaced every year whether or not a person was obese.
Despite that replacement rate, another aspect of the study with a larger sample
of people revealed that the total number of fat cells per person remained
relatively constant over time. Even extreme weight-loss strategies, such as
bariatric surgery, did not reduce the number of fat cells in study subjects.
Aha!
The tightly regulated number of fat cells in adulthood may explain why it seems
easy to gain back lost weight, Buchholz said.
If you already have more fat cells from adolescence than other people, "it's
harder to become thin," Buchholz told LiveScience.
The study raises a new mystery: Something tells the body to make a new fat cell
when another dies, Buchholz said. In the future, if scientists could interfere
with this turnover, they might actually reduce fat-cell number in adults, he
said.
The findings, detailed in the May 4 online issue of the journal Nature, suggest
that the focus for controlling obesity should be on children, said Dr. Jeffrey
Gimble, who studies fat stem cells at the Pennington Biomedical Research Center
in Baton Rouge and was not involved in the research. The idea is that if the
number of fat cells is capped by age 20, then the smart approach is to prevent
their formation in children.
Obesity prevention in the early years could have "a lifetime impact," Gimble
said.