Once upon a time, experts believed fat cells were no more than
inert tissues that merely stored energy, enlarged extremities and
generally got in the way of people trying to move around. Popular
opinions have changed, however, thanks to the intense interest in
fat in order to find solutions to the U.S. obesity crisis.
Experts are realizing fat cells are dynamic
and complex structures that affect many crucial bodily functions.
These new insights are helping scientists better understand:
- How fat forms on bodies
- Why it hangs on so long
- How it causes disease
Fat cells work to dispatch many potent signals to tissues throughout
the body, including reproductive organs, the brain, liver and immune
system. A better understanding of how fat communicates with the
rest of the body, scientists say, could lead scientists toward a
cure for obesity and all the diseases related to it. That's why
some drug companies are racing to find ways to manipulate hormones
so that people can lose weight and avoid obesity.
Fat does a great many things, far beyond
regulating a body's energy system and creating new fat cells:
- Turns the body's immune system up or down
- Influences blood clots and when blood vessels constrict
- Regulates when a women can reproduce
Some scientists theorize there are dozens more functions waiting
to be discovered, including a few that may affect mood and behavior
beyond eating and hunger. Others believe society's opinion of obesity
could change significantly, ridding people of a social stigma by
strengthening the case that obesity is a biological problem, not
merely a matter of free will.
Opinions began to change a decade ago when scientists identified
leptin, the hormone produced by fat cells, that tells the brain
a number of things, including how much fat a body has. That's when
drug companies began thinking leptin could be controlled and used
as an obesity drug. So far, no progress has been made. The discovery
of leptin also created a way of looking at fat as an endocrine organ
not unlike the thyroid and adrenal glands.
Part of that complex and fine-tuned communication system between
fat and other organs is adiponectin, a hormone that lowers the production
of blood glucose in the liver and increases muscle burning to make
energy. Scientists say this hormone also affects the sensitivity
of cells to insulin, which may explain how obesity increases one's
risk of diabetes. Curiosity about how adiponectin works probably
explains why one drug company is studying it to treat diabetes and
spur weight loss.
After the importance of adiponectin was recognized, scientists
found resistin, another fat cell hormone that may play an important
role in storing energy and insulin sensitivity.
Researchers have also recently discovered fat tissue is made up
of much more than fat cells. In fact, fat tissue, combined with
macrophages--key immune system cells--produce powerful substances
that assist in regulating the body's immune system. Some theorize
fat became closely connected to immune function over time because
the body needs energy when threatened.
A surplus of these substances, researchers say, likely triggers
unnecessary inflammation which could explain why obesity increases
the chances of so many ailments like cancer, diabetes and heart
disease.
Fat cells send signals so that blood vessels constrict may describe
why obesity increases one's risk for stroke and heart attack. Conversely,
they spur the growth of blood vessels and cells, which may be why
obesity raises one's chances of cancer.
Washington
Post July 12, 2004
| 