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The
Pima Indians have a so-called "thrifty gene" that enables
them to store fat efficiently during times of scarcity.
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Ten
years ago, Jeffrey Friedman,
M.D., Ph.D., started a revolution in our understanding of how the
body controls weight.
It all began with some very fat mice. The mice had a genetic defect
that prevented fat cells from producing a hormone that signals the
brain when there's enough fat.
Friedman called the hormone leptin, and there was great excitement
when some obese people were found to be leptin deficient.
But most obese people are not leptin deficient. As Friedman explains
to Alan, the body's weight control system involves a complex array
of hormones and other biological factors that we are only beginning
to understand.
Hormone signals are constantly received and processed in the region
of the brain called the hypothalamus. Leptin signals how much fat
is in the body. Ghrelin indicates hunger and fullness. And peptide
YY sends information about the intestines.
These signals, says Friedman, somehow combine with higher cognitive
thoughts, emotions and sensory information to help determine whether
we eat or don't eat.
The
fact that people have different tendencies toward obesity is evidence
for the complexity of our eating control system. For instance, the
Pima Indians have a so-called "thrifty gene" that enables them to
store fat efficiently during times of scarcity. But, when food's
plentiful, the Pimas get too fat.
Trying
to lose weight involves a deliberate attempt to manipulate our body's
weight control system, and Friedman says our bodies often resist weight
loss. As a person's fat stores shrink, less leptin is produced. When
leptin is low, appetite increases while metabolism decreases--making
it pretty tough to lose weight. Losing large amounts of weight--and
keeping it off--may actually be impossible, Friedman says.
Considering the complexity of our weight control system and the number
of factors that influence weight loss and gain, it's perhaps no wonder
that about 85 percent of dieters regain their weight within five years.
For
more on this topic, see the web feature:
Battling the Bulge
Fighting
the Thrity Gene
Science
Hotline - Jeffrey Friedman
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