Most people think of fat as an inert blob,
but fat cells release powerful chemicals.
In obese people, the fat tissue often
produces too many bad hormones and too few good ones, says
Susan Fried, director of the Clinical Nutrition Research Unit
of Maryland at the University of Maryland School of Medicine
Fried and other scientists discussed
the latest research on fat cells here at the annual meeting
of the Obesity Society. Fried talks about the relationship
between obesity and fat cells.
Q: Do people have different numbers
of fat cells?
A: A person at a healthy weight might have 10 billion to 20
billion, and an obese person can have up to 100 billion. Babies
are born with about 10 billion. You naturally increase the
number of fat cells, like other kinds of cells, as you grow.
Q: Is everybody born with the same
number of fat cells?
A: No. There is a genetic component to how many you have,
but I would say less than 5% of obese people have a genetic
tendency to have a greatly excess number. It appears in animal
experiments that animals that are overnourished in the womb
and shortly thereafter tend to have more fat
The number can increase at any time if
you overeat long enough and hard enough. When your fat cells
get to a maximum size, they send a signal to (fat-precursor)
cells to become full-fledged fat cells. It may be that having
too many hungry fat cells somehow makes us eat more.
But overweight people (those who are
not obese but are one to 30 pounds over a healthy weight)
don't generally have an excess number. You can gain 30 pounds
easily by increasing the size of current fat cells and not
adding new ones.
Q: What do white fat cells do?
A: White fat cells store energy and produce hormones that
are secreted into the blood. In theory, if we overeat, our
fat cells will produce a little more of the hormone leptin,
which will go to our brain and tell us we have plenty of energy
down here; not to eat any more. If it worked perfectly, no
one would get fat, but it doesn't work perfectly, so many
of us do get fat.
When fat cells are small, they produce
high amounts of some hormones such as adiponectin. It is a
good guy because it keeps the liver and muscles very sensitive
to insulin and fights diabetes, heart disease and other diseases.
But in obese people, fat cells tend to shut down the production
of adiponectin, and that has bad effects on health, and it's
one reason people develop diabetes and heart disease.
Q: Does losing weight shrink the size
of your fat cells?
A: If you are eating less energy than you require, your cells
release fat for fuel and then shrink. If you are obese and
have 100 billion fat cells and you lose a lot of weight, your
fat cells may go down to a normal size, but you still have
100 billion. So you may still be overly fat, but you will
be healthier since small fat cells produce more of the good
fat hormones like adiponectin.
Q: Can you explain the new discoveries
about brown fat?
A: While a white fat cell stores energy, a brown fat cell's
job is basically to generate heat. We always thought brown
fat was only in human babies and helped keep them warm. Now
there is more evidence that there are more brown fat cells
in adults than we originally thought. Brown and white are
not really related because they don't come from the same precursor
cell or stem cell.
Brown fat cell comes from the same kind
of precursor cell as a muscle cell. Even though there are
very few brown fat cells in adult humans, it looks like there
is a lot of variability between people. There is increasing
evidence that some humans, particularly lean ones, tend to
have brown fat cells mixed in with their white fat cells in
some regions of their body. So if we can figure out how to
persuade the body to make more brown fat cells, we may be
able to fight the tendency to gain excess weight.